REVIEW Open Access
Crowdsourcing, citizen sensing and sensor web
technologies for public and environmental health
surveillance and crisis management: trends, OGC
standards and application examples
Maged N Kamel Boulos1,2*
, Bernd Resch3,4
, David N Crowley5,6
, John G Breslin5,6
, Gunho Sohn7,8
, Russ Burtner9
,
William A Pike9
, Eduardo Jezierski10
and Kuo-Yu Slayer Chuang11
Abstract
’Wikification of GIS by the masses’ is a phrase-term first coined by Kamel Boulos in 2005, two years earlier than
Goodchild’s term ‘Volunteered Geographic Information’. Six years later (2005-2011), OpenStreetMap and Google
Earth (GE) are now full-fledged, crowdsourced ‘Wikipedias of the Earth’ par excellence, with millions of users
contributing their own layers to GE, attaching photos, videos, notes and even 3-D (three dimensional) models to
locations in GE. From using Twitter in participatory sensing and bicycle-mounted sensors in pervasive
environmental sensing, to creating a 100,000-sensor geo-mashup using Semantic Web technology, to the 3-D
visualisation of indoor and outdoor surveillance data in real-time and the development of next-generation,
collaborative natural user interfaces that will power the spatially-enabled public health and emergency situation
rooms of the future, where sensor data and citizen reports can be triaged and acted upon in real-time by
distributed teams of professionals, this paper offers a comprehensive state-of-the-art review of the overlapping
domains of the Sensor Web, citizen sensing and ‘human-in-the-loop sensing’ in the era of the Mobile and Social
Web, and the roles these domains can play in environmental and public health surveillance and crisis/disaster
informatics. We provide an in-depth review of the key issues and trends in these areas, the challenges faced when
reasoning and making decisions with real-time crowdsourced data (such as issues of information overload, “noise”,
misinformation, bias and trust), the core technologies and Open Geospatial Consortium (OGC) standards involved
(Sensor Web Enablement and Open GeoSMS), as well as a few outstanding project implementation examples from
around the world.
Keywords: Citizen Sensing, Sensors, Social Web Crowdsourcing, Twitter, Geo-mashups, Semantic Web, OGC Sensor
Web Enablement, OGC Open GeoSMS, 3-D Visualisation, Natural User Interfaces, Public and Environmental Health,
Crisis Informatics
State-of-the-art review
’Wikification of GIS (Geographic Information Systems)
by the masses’ is a phrase-term first coined by Kamel
Boulos in 2005 [1], two years earlier than Goodchild’s
term ‘Volunteered Geographic Information (VGI)’ [2].
Six years later (2005-2011), Google Earth (GE) [3] is
now a full-fledged, crowdsourced ‘Wikipedia of the
Earth’ par excellence, with millions of users contributing
their own content to it, attaching photos, videos, notes
and even 3-D (three dimensional) models to locations in
GE.
GPS (Global Positioning System) traces received from
commuters via their Internet-enabled mobile devices
can be used to generate real-time traffic updates, while
geo-tagged, street-level audio samples recorded and
uploaded by pedestrians using their location-aware
smartphones can be aggregated to create citywide noise
(pollution) maps for various times of the day and week
* Correspondence: mnkamelboulos@plymouth.ac.uk
1
Faculty of Health, University of Plymouth, Drake Circus, Plymouth, Devon
PL4 8AA, UK
Full list of author information is available at the end of the article
Kamel Boulos et al. International Journal of Health Geographics 2011, 10:67
http://www.ij-healthgeographics.com/content/10/1/67
INTERNATIONAL JOURNAL
OF HEALTH GEOGRAPHICS
© 2011 Kamel Boulos et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative
Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly cited.
[4]. Such applications are often referred to as ‘crowdsourcing’
or ‘participatory sensing’ applications, since
they are capitalising on the power of the masses (or
‘crowds’) and relying on citizen participation to achieve
their goals. They are becoming increasingly common
these days, thanks to the rapidly growing affordability,
availability and adoption rates in recent months and
years of Internet-enabled and location-aware mobile
devices, such as tablets and smartphones [5].
Geolocation-aware mobile crowdsourcing apps (short
for applications, especially those designed to run on
smartphones and tablets), such as Love Clean Streets
[6], HealthMap’s Outbreaks Near Me [7] and MedWatcher
(drug safety surveillance) [8], and the San
Ramon Valley (CA, USA) Fire Department app (a realtime,
geo-aware lifesaving app that alerts ‘citizen responders’
trained in CPR (CardioPulmonary Resuscitation) as
soon as a cardiac arrest has been reported to emergency
services) [9], are leveraging the power of the Social Web
(’Web 2.0’) and smartphones to provide unprecedented
levels of citizen engagement and participation in their
local and wider communities.
Crowdsourced mapping examples (some are in realtime)
include Sickweather [10], an online social health
network for sickness (e.g., flu) forecasting and mapping;
the crowdsourced real-time radiation maps [11] that
made the news headlines following Japan’s Fukushima
Daiichi nuclear disaster in March 2011; and the ‘Lunch
Break’ Web map [12], a poll and map launched by the
Wimpfheimer-Guggenheim Fund for International
Exchange in Nutrition, Dietetics and Management that
provides a unique look at lunchtime eating patterns in
North America. These apps and maps, freely available to
the public online, are excellent examples of how crowdenabled
systems are revolutionising the way we tackle
problems and allowing us to monitor and act upon
almost anything, anywhere, in real-time.
GeoChat [13] and Ushahidi [14] are two open source
platforms that enable the easy deployment of crowdsourced
interactive mapping applications with Web
forms/e-mail, SMS (Short Message Service) and Twitter
[15] support. They can be freely downloaded and
deployed on one’s own server by anyone with the appropriate
technical expertise or used as online services
hosted by their respective platform providers (e.g.,
Crowdmap [16] is the hosted version of Ushahidi).
Mobile apps are available for accessing Ushahidi on
smartphones and tablets, e.g., for the Android platform
[17].
In Cambodia, the Ministry of Health uses GeoChat for
disease reporting and to send staff alerts and rapidly
escalate response to potential outbreaks, while in Thailand,
more than 900 facilities within the Hospital Network
exchange information and get alerts to monitor
influenza outbreaks in real-time from facilities across
the country. GeoChat was also deployed during the
2010 earthquake relief efforts in Haiti to coordinate field
teams’ activities and provide remote support from outside
the earthquake zone [13]. Ushahidi and Crowdmap
can be similarly used to crowdsource and map crisis
information from multiple data streams in real-time;
see, for example, Ushahidi’s crowdsourced map of the
2010 Haitian earthquake [18] and Thailand Flood Crisis
Information Map at [19] (these latter two examples are
also a good demonstration of Ushahidi’s ‘dynamic timeline’
feature for tracking crowdsourced reports on the
map over time and filtering the data by time). Maps of
this kind provide situational awareness, which is essential
in crisis management operations.
Real-time mining of indirectly (i.e., unsolicited, not
obtained via a formal reporting form/not originally
meant for posting to a specific crowdsourcing effort)
self-reported and sousveillance information harvested
from aggregates of Twitter and other social network
feeds can offer useful data and insights about unfolding
trends and emerging crowd behaviours at times of crises
[20]. However, such (raw) data obtained from Social
Web feeds often contain variable amounts of “noise”,
misinformation and bias (which can get further “amplified”
through the viral nature of social media) and will
usually require some advanced forms of filtering and
verification by both machine-based algorithms and
human experts before becoming reliable enough for use
in decision-making tasks. WSARE (What’s Strange
About Recent Events)-type algorithms [21] and platforms
such as SwiftRiver [22] (open source, provided by
Ushahidi) can prove helpful in trying to filter the Social
Web “firehose”.
(Twitter can also act as a ‘publish-subscribe’ infrastructure
for non-human sensors and smartphones to
directly post (i.e., automatically push time, date and
location-stamped sensor readings to Twitter) and consume
(i.e., subscribe to, and data mine, sensor reading
tweets) more crisp and objective observations about our
physical world, using some agreed form of ‘sensor tweeting
standard’ [23] or ‘Twitter Annotations’ (tweet
metadata).)
Besides human-triggered and/or generated input, more
and more medical and other specialised sensor devices
such as environmental and weather sensors, either fixed
(e.g., at home, in buildings/rooftops or street furniture)
or mobile (e.g., vehicle-mounted as in [24] or held/worn
by commuting user), are being equipped these days with
M2M (Machine-to-Machine) SIM (Subscriber Identity
Module) cards or with Bluetooth or some other form of
wireless communication with a suitable in-range relaying
device, e.g., a user-held smartphone, to enable these sensors
to send additional forms of non-human input to a
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remote aggregator service. These specialised sensor
devices, usually operating within a network (or more
than one network) of other distributed sensors, can
automatically (or autonomously, depending on setup)
gather and relay location (and/or person)-specific observations
at intervals (scheduled or when required) or
continuously, in real-time, to remote stations or ‘situation
rooms’. There (in the latter remote centres) data
from multiple device sensors and/or human observers,
covering one or more than one place, are collated, analysed,
contextualised/triangulated (including with other
non-sensor data) and summarised/visualised in different
ways as appropriate, in real-time, near-real-time and/or
for past points in time, e.g., DERI’s live sensor geomashup
[25,26] (Figure 1), to support monitoring, surveillance
and decision-making tasks of various kinds.
While the 2-D (two-dimensional) user interface of
DERI’s live sensor geo-mashup (based on Google Maps)
is very functional for ‘situation room’ purposes,
improvements can still be made to realise the full vision
of emergency/public health virtual situation rooms
described in [27]. For example, the ‘3D Town’ project at
York University, Canada, is working to bring real-time
sensing, tracking and surveillance of moving vehicles
and people in outdoor and indoor city environments to
static 3-D city models and 3-D virtual globes, thus making
the latter truly dynamic by visualising live data on
them [28], while colleagues at Pacific Northwest
National Laboratory, USA, are developing future spatially-enabled
work environments for emergency management,
which they call ‘Precision Information
Environments’ (or PIEs) [29]. PIEs aim at providing tailored
access (i) to information from multiple data
streams/sensors, and (ii) to analysis, simulation, decision
support, and collaboration/communication capabilities.
PIEs achieve this through novel interactions that adapt
to the varying users (e.g., first responders, policy makers
and the public) and phases of emergency management
(from planning to response, recovery and mitigation) in
distributed situation room and field settings (see concept
video at [30]).
The Open Geospatial Consortium’s (OGC) Sensor
Web Enablement (SWE) standards allow developers to
make all types of sensors, transducers and sensor data
repositories discoverable, accessible and useable (for
tasking, eventing and alerting) via the Web by defining
service interfaces that enable an interoperable usage of
sensor resources. A Sensor Web based on SWE services
and standardised interfaces hides the heterogeneity of its
underlying sensor network, as well as the complexity of
its communication details and various hardware components,
from the applications that are built on top of it,
thus making the development and deployment of such
applications a much easier task [31,32].
Another OGC standard, Open GeoSMS, enables the
interoperable communication of location coordinates
and content between different location-aware devices
and applications using the extended Short Message Service
(SMS), while maintaining human readability of the
content [33]. Open GeoSMS has been implemented in
Ushahidi and in the open source Sahana Disaster Management
System [34] and has proven very useful in
emergency and crisis management situations.
Following on from this condensed, bird’s eye review of
the field, the remaining sections of the paper will now
shed some additional light on a select number of key
issues, core standards and technologies, as well as a few
outstanding project implementation examples related to
the subject.
A closer look at citizen sensing (participatory sensing)
and ‘human-in-the-loop sensing’ in the era of the Mobile
and Social Web
In 1999, before the advent of Foursquare [35], mobile
Twitter clients or GPS and sensor-enabled phones, a
somewhat prescient Neil Gross in Bloomberg Business
Week said:
“In the next century, planet earth will don an electronic
skin. It will use the Internet as a scaffold to support
and transmit its sensations. These will probe
and monitor cities and endangered species, the atmosphere,
our ships, highways and fleets of trucks, our
conversations, our bodies-even our dreams [36].”
This view of sensors as ubiquitous and being
embedded into our everyday environment can be seen
as an accurate description of human-sensor interaction
today with the advancements in wireless sensor networks
and with the huge growth in the use of mobile
devices which contain multiple sensors. The unprecedented
96% growth in smartphone sales (in Q3 2010)
[5,37] displays the availability and prevalence of these
relatively cheap mobile sensing devices that enable
Internet users to become sensing devices.
In the past ten years, we have seen the growth of
online social networks and an explosion in user-generated
content on the Web published from mobile devices
to social platforms such as Twitter. Twitter is a microblogging
platform founded in 2006, which by September
2011 had 100 million active monthly users and 400 million
monthly visitors [38]. As of June 2011, Twitter processed
200 million posts (or ‘tweets’) per day [39]. In
parallel with this growth of social networks, there has
been a surge in sensor networks, many of which are also
connected to the Internet, e.g., [40]. These usually consist
of multiple static or inert sensors that capture certain
readings from their environment whenever they are
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programmed to do so. In addition, many people are now
carrying some form of sensor-laden device - a mobile
phone, a tablet, a fitness device - from which sensor
readings can also be retrieved. This is sometimes called
‘human-in-the-loop sensing’, but cars, animals and other
moving entities can also incorporate sensors.
Cuff et al. propose that pervasive computing has
moved from the laboratory into the natural environment
[41], laying the foundations for Mark Weiser’s concept
of ubiquitous computing, which he sees as the “availability
of computers throughout the physical environment,
virtually, if not effectively, invisible to the user“
[42,43]. Cuff et al. describe mobile devices as “passive
sensors that can silently collect, exchange, and process
information all day long“ [41]. This style of sensing is
called ‘urban sensing’ due to its suitability for large
urban areas with high population density, but could be
implemented in any environment. Campbell et al. view
Figure 1 Screenshot of DERI’s LSM (Linked Sensor Middleware) live sensor geo-mashup. Screenshot of the interface available at [21]
showing near-real-time data obtained from a ‘traffic sensor’ in London, UK.
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“urban sensing as a departure from existing thinking on
sensor networks because people are no longer just consumers
of sensed data about some natural phenomenon or
ecological process. Rather data about people are now
sensed and collected such that the sets of producers and
consumers of sensed data now overlap; people are ‘in the
loop’ and may participate in both roles [44].”
Cuff and colleagues raise two issues with urban sensing
(which affect all human-in-the-loop sensing generally):
bad data processing and the ‘observer effect’ [41].
Eradicating these issues or lessening their effect by verification
of data with other sensor nodes/human input
data can be accomplished but depends on the density of
the network and existence of other related data. Chatzigiannakis
et al. discuss technical challenges to pervasive
applications in urban sensing, which include multiple
data streams of varying data types, different skill/knowledge
levels of users, and privacy and security of user
data [45]. Some of these challenges can be overcome by
using standardised sensor descriptions and models; the
Semantic Sensor Network ontology (SSN) is an example
of this and creates a domain-independent and full
model for sensing applications by merging sensorfocused
(e.g., SensorML [46], part of OGC SWE), observation
focused (e.g., Observations and Measurements
[47], part of OGC SWE), and system-focused models
[48]. Figure 2 presents an overview of the classes and
properties in the SSN ontology. The ontology representation
of a sensor links together what it measures (the
domain), the physical sensor (the grounding), and its
functions and processing (the models). The SSN ontology
does not try and describe every sensor and scenario
but instead develops a general representation of sensors
and a domain description; it relies on upper-level ontologies
to define the domain and on an operation model
that describes how the measurement is implemented
[49].
Burke et al. assert that “participatory sensing will task
deployed mobile devices to form interactive, participatory
sensor networks that enable public and professional users
to gather, analyse and share local knowledge“ [50]. They
envisage mobile devices equipped with cameras, GPS,
and microphones acting as sensor nodes or as locationaware
collection instruments. This idea of a mobile
device wireless sensor network removes many of the
barriers to implementing urban sensor networks. Barriers
and challenges exist such as (i) initial cost of the
nodes, (ii) the need to position/distribute the sensors
appropriately, and (iii) implementing a network dense
enough to build in redundancy if individual sensor
nodes fail. Welsh examines issues with implementing
wireless sensor networks such as random positioning
(redundant in scientific experiments, as location is often
a requirement and due to cost of nodes), the cost and
Figure 2 SSN (Semantic Sensor Network) ontology.
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size of nodes, and creating dense networks [51]. Density
raises issues in other ways through redundancy and network
capabilities - redundancy is beneficial, but network
capabilities may be limited, so redundancy might not be
possible to implement. Mobile cellular networks also
suffer from this density challenge when a large amount
of users using bandwidth can cause a flooding of the
network. This network flooding can often occur during
times of crisis as seen on 13 July 2011 in Mumbai,
India, where after three explosions mobile networks
were unusable by government officials and the general
populace [52,53].
Burke et al. discuss the core network services in a participatory
application, which include the concept of network-attested
location and time, physical context using
sensors (accelerometer, compass to work out direction
device is facing), distance between devices/nodes, and
context resolution control which controls the level of
information shared by any one user or sensor. They
foresee different applied areas for the research field in
public health, urban planning, cultural identity (images
with location, time, and context), and natural resource
management, and state the goal of these services as placing
“users in the loop of the sensing process and aiming
to maximise the credibility of data they collect“. They
see these applications as an aid to researchers, policymakers
and the public that “use data to understand and
persuade; higher quality data tend to generate more significant
action and better understanding which leads to
better planning, and policy decisions“ [50]. Citizen sensing
and “slogging” (sensor logging) [54] concepts then
emerge from this participatory sensing research where
citizen sensors embedded in their environments report/
analyse their surroundings.
Sheth describes users of the Internet or Web-enabled
social community as citizens, and the ability to interact
with Social Web (’Web 2.0’) services can augment these
citizens into citizen sensors, “that is, humans as citizens
on the ubiquitous Web, acting as sensors and sharing
their observations and views using mobile devices and
Web 2.0 services“ [55]. Goodchild discusses citizen sensing
in the field of Volunteered Geographic Information
(VGI) and sees citizens as a network of human sensors
with over “6 billion components, each an intelligent
synthesiser and interpreter of local information. One can
see VGI as an effective use of this network, enabled by
Web 2.0 and the technology of broadband communication“
[2]. He sees each human sensor node as being
“equipped with some working subset of the five senses
and with the intelligence to compile and interpret what
they sense, and each free to roam around the surface of
the planet“ [2]. Events, online social networks, or networks
created more spontaneously by events can create
citizen sensor networks - “an interconnected network of
people who actively observe, report, collect, analyse, and
disseminate information via text, audio or video messages“
[55]. It is this ‘human-in-the-loop sensing’ combined
with Social Web services and mobile computing
that leads to the creation of citizen sensors and differentiates
it from urban or participatory sensing. Sheth
lists the advantages of ‘human-in-the-loop sensing’ as:
• Machines are good at symbolic processing but poor
at perception;
• Machines are good at continuous, long-term sensing
but humans can contextualise, discriminate and filter;
and
• Learning, adapting, background knowledge, common
sense and experience [55].
Humans continuously subconsciously and consciously
sense, process, and induce inferences from events
around them in real-time. Sense in this context is
defined as one of the methods for a living being to
gather data about the world: sight, smell hearing, touch,
and taste [56]. Humans also leverage past experiences,
background knowledge, and reasoning to extract meaning
from often confusing or new experiences. Srivastava
and colleagues define the following different participation
roles of human-centric (or ‘human-in-the-loop’)
sensing:
• (Humans as) information source;
• Measurement collection;
• Sensor data processing;
• Information sharing; and
• Information fusion and analysis [57].
These roles show that the human sensors perform
processing and analysis of the collected data [57]. This
pre-processing/processing of sensory data from experience/background
knowledge is what differentiates our
sensing capabilities from hardware sensors. Sensing can
be defined as an operation of a sensor, the detection of
a physical presence and the conversion of that data into
a signal that can be read by an observer or an instrument
[58]. In citizen sensing, a sensor is not necessarily
a hardware sensor but can be a virtual sensor or a
human interpreting sensory data. Sheth also envisages
that microblogging platforms (where users can post
short textual messages, Internet links, attached videos,
and pictures) as low-effort publishing services are of
particular interest to citizen sensing due to the large
scale of users on platforms such as Twitter, which
enables the user to post from mobile devices with minimum
effort through mobile applications [55]. As microblogging
lends itself to instantaneous updates, creation
of data related to events around the world is posted
before it can be reported on by more traditional media
methods or even by blog or blog-like services. He uses
the example of Twitter posts during the Mumbai terrorist
attacks in November 2008, when Twitter updates
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and Flickr [59] feeds by citizens using mobile devices
reported observations of these events in almost realtime
[60].
These events are spatially, temporally, and thematically
(STT)-linked; Sheth describes related events as situations.
These events and series of related events can
rapidly create networks of users posting information,
but currently it can be difficult to track and collate all
this information and make sense of all related posts.
These events can be used to describe a model where,
according to Westermann, events are “the basic unit for
organising data and for user interaction“ [61]. Jain
defines this event-driven model as a “human-centred
computing system that will give users a compelling
experience by combining quality content, carefully
planned data organisation and access mechanisms“ [62].
These events can lead to ad-hoc spontaneous networks
that are not necessarily socially interlinked but are
event-connected, where such events are described in
spatial, thematic, and temporal terms. These events as
viewed by multiple citizen sensors can have different
perspectives taken from the citizen’s own assessment of
the event, which can also influence the reporting. Kwak
et al. discuss the role of Twitter as a social network or
as a news media; their research shows that a retweet
(where a retweet or ‘RT’ on Twitter describes an emaillike
forwarding mechanism practised by Twitter users to
show the origin of the post/tweet) reaches an average of
1,000 users and this reach value is independent of the
number of followers of the original poster [63]. Retweet
trees show the spread of news and other interest pieces
on Twitter and show the usefulness of Twitter as an
event tracking mechanism and as a ‘citizen journalism’
platform. Sheth [64] describes how semantic annotation
(using Resource Description Framework - in - attributes–RDFa
[65]) of sensor data and then citizen sensor
data [55] can aid metadata already embedded within
user posts on Twitter and Flickr. This semantic annotation
would assist thematic analysis and aid in disseminating
information from informal SMS-style language.
The building of semantic domain models about specific
event types but in a generalised event model to describe,
for example, natural disasters instead of specific types,
and models to describe geographical locations would
also aid in the language processing of such informal
text. These general domain models would also remove
the need to create more formal domain models that
require agreement by specialised domain experts.
An example of a citizen sensing application, Twitris
[66] is used to show STT analytics and how the system
can be deployed to identify events [67]. Nagarajan et al.
describe the challenges to developing citizen sensing
platforms and gathering topically relevant data [68], as
Twitter does not categorise users’ posts, but instead
Twitter’s search API (Application Programming Interface)
[69] is used with extraction of hashtags. The
retrieved hashtags phrases are then used as seed keywords
and seed keywords are generated by using Google
Insights for Search [70]. This works on the presumption
that high volume search terms describe events and are
of high interest to users [68]. In this work hyperlinks to
external content were ignored and only textual content
was studied (hyperlink analysis was added in Twitris 2.0
[71]).
At present, GPS adds location to the data of the post
made, but in the field of multi-sensor context awareness,
researchers are always examining ways to augment
devices with awareness of their situation and environment
to add contextual understanding. As Gellersen et
al. assert “position is a static environment and does not
capture dynamic aspects of a situation“ [72]. This idea
can be applied to most single sensor data, but with
multi-sensor context awareness, the diverse sensor readings
are combined and then with processing, situational
context can be derived. Mobile phones and tablet-style
devices come equipped with an array of sensors and are
positioned ideally to be the ubiquitous computing and
communications devices in the near future. These sensors
enable mobile phone sensing application domains
such as healthcare and environmental monitoring [73]
and can be utilised within the citizen sensing field.
Bringing together the best of experts, crowds, and
machines
One needs to adopt concurrently a set of three practices
for rapid analysis of large volumes of information:
expert analysis, crowdsourcing (especially engaging networks
of professionals in the health system, who have
local knowledge and can do contributions from their
perspectives, not only ‘public crowds of citizens’) and
machine learning. Each of these three items provides
useful data by itself, but used together, they are able to
counter-balance each other’s strengths and weaknesses,
as shown in Figure 3.
Experts make decisions based on understanding data
sources and the mechanics behind health events (e.g.,
transmission modes of diseases, time lags (incubation
period) between infection and (onset of) symptoms,
knowledge of the typical behaviour of patients, etc.).
These experts can very rapidly generate a hypothesis
about an unfolding event or validate, confirm or deny a
certain characterisation. They also have in-depth knowledge
about response protocols and sources of specialised
data.
Experts, however:
• Are few in number and their time is precious;
• Are increasingly specialised, which allows them to
make blink decisions correctly within their domain, but
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requires collaboration across other areas of expertise to
contribute a ‘complete picture’ of a situation; and
• May have little local knowledge about local behaviours
in an area where there may be an unfolding
outbreak.
During the 2009 H1N1 influenza pandemic crisis, it
was clear that the Internet and open data played a big
role in capturing a ground truth of how people were
reacting to the pandemic. Tamiflu (Oseltamivir, an antiviral
drug) availability, hospital queue lines, and impact
on medical care provider stress levels were all extensively
blogged, tweeted, and shared via listservs and
other modes of communication. This provided greater
quantity and quality of information than was expected.
Information from ‘crowds’ and communities of practice
can be very useful, with the following considerations
in mind:
• Twitter and other social media can disseminate both
valid and invalid information [74]. Crowdsourced ‘data’
have a tendency to be resistant to nuance and correction;
especially in social media, once a meme snowballs
in the ‘echo chamber’, it can be very hard to correct (or
‘counter-tweet’) and the crowd is sometimes not so fast
at changing course;
• Crowds often have no immediate way to discern
truth from falsehood; what gets propagated is the ‘popular’
opinion shaped by the most prominent personalities,
beliefs and agendas of the individuals in the ‘crowd’.
Technically-savvy citizens also introduce an interesting
skew in the velocity with which their ideas spread and
get shared; even more if there are political agendas
involved. For example, tools to visualise H1N1 spread
became popular more on the basis of visual appeal than
quality of the data or the processes used to generate or
validate them (but opinions are not all too bad, and
opinion mining and sentiment analysis algorithms still
have an important place in some Social Web mining
and surveillance applications [75]);
• Crowds are prone to add opinion to data; which
sometimes sticks more than the credible data themselves.
Separating opinion and credible data through
expert interpretation and curation, both centralised and
decentralised, is important (in de-centralised curation,
specific statements of fact expressed or extracted from
citizen-generated information are validated, refuted, and
expanded by the citizens themselves in a more distributed
system (cf. concepts of peer reviewing and darwikinism
[76]); and
• There are a few agencies (e.g., [77]) that have organisational
or procedural channels specifying how to aggregate
and incorporate information emerging on the
Internet in decision making.
As for algorithms, in the business and finance sector,
Derwent Capital and Bloomberg (with WiseWindow)
are said to be already using Twitter mining algorithms
in making useful stock market predictions with good
accuracy [78,79]. Machine learning algorithms can be
used to extract useful information from large amounts
of data. Most machine learning applications in health
use supervised learning, a subset of machine learning
that uses ‘feedback’ (from humans or other systems) to
improve its learning over time. Common uses of
machine learning include:
• Feature extraction: For example, extracting ICD-9
(International Classification of Diseases) codes and
references to syndromes or diseases from text, as well as
interpreting text to infer time, location, people, etc.
referred to in it;
• Classification: Being able to classify, group or tag
information based on some explicit or unknown criteria;
Figure 3 Integrating experts, crowds, and signal processing algorithms.
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• Clustering: Machines can process vast amounts of
data and present correlations and proximities that
escape the human eye and brain, sometimes discovering
non-obvious correlations between variables; and
• With large amounts of data available, it is not even
necessary to have a deep understanding of the relationships
within the data themselves: machines can on their
own distil the noise from the relevant correlations
through successive optimisation.
However, machine learning has shortcomings of its
own, when used in isolation:
• Some algorithms process signals in a way that is
more specific than sensitive, meaning that important
signals may be missed (false negatives). A combination
of algorithms is important to draw different types of
events and event features from undifferentiated data;
understanding which algorithms, through experience, is
essential;
• Algorithms need to be thoroughly validated and
tested; and each new situation may place a new challenge
on a given algorithm that may not allow the
assessment of the quality of the algorithm in real-time;
• Algorithms need data to train and feedback to learn.
Sometimes this learning phase makes it hard to get
value ‘out of the box’;
• Humans have a tendency to become “lazy” over time
and experience with accepted algorithms, where overdependency
and improper cross-checks of an algorithm’s
results may result in missed or misinterpreted
signals;
• Low social acceptance in some cultures of systems
that do not function in a way that is predictable or
describable by a human; and
• Past misuse of machine learning with little understanding
of the cognitive science underpinnings of
human communication has led users to fear (and AI
(Artificial Intelligence) experts to boast) that an algorithm
could be put on par with a human. State-of-theart
cognitive theories (Winograd, Flores, etc.) show that
commitments (statements of fact) can only be provided
by humans; and therefore provide a better framework
for understanding where machine learning fits. In simpler
terms: - Should an algorithm declare a health emergency?
No - because there is no commitment behind it.
Can an algorithm help present data to an expert or
authority with ‘suggestions’ and ‘red flags’, and then the
authority can declare a health emergency? By all means,
and this is a smarter design.
Standardisation enables interoperability: OGC Sensor Web
Enablement Initiative and Open GeoSMS
The vision of pervasive sensing through ‘citizens as sensors’
poses considerable challenges in terms of interoperability
involving data formats, service interfaces,
semantics and measurement uniformity. Thus, one key
prerequisite to achieve this vision is the broad usage of
open sensor standards.
The Sensor Web Enablement Initiative (SWE) by
the OGC (Open Geospatial Consortium) has recently
gained importance through its maturity and its broad
support from research and industry. SWE seeks to provide
open standards and protocols for enhanced operability
within and between multiple platforms and
vendors. In other words, SWE aims to make sensors discoverable,
query-able, and controllable over the Internet
[80]. Currently, the SWE family consists of seven
standards:
• Sensor Model Language (SensorML)
This is a general schema for describing functional models
of the sensor. It provides an Extensible Markup Language
(XML) schema for defining the geometric,
dynamic and observational properties of a sensor. Thus,
SensorML serves for discovering different types of sensors,
supporting processing and analysis of the retrieved
data, as well as the geo-location of observed values.
Information provided by SensorML includes observation
and geometry characteristics, as well as a description
and a documentation of the sensor, and a history of the
component’s creation, modification, inspection or
deployment.
SensorML aims to provide descriptions of sensors and
sensor systems for inventory management, to supply
sensor and process information in support of resource
and observation discovery. Furthermore, SensorML aims
to allow for geo-locating observed values (measured
data), to provide performance characteristics (e.g., accuracy,
threshold, etc.) and to offer an explicit description
of the process, by which an observation was obtained.
An important capability of SensorML that has to be
mentioned considering the background of this paper is
the formation of sensor classes, i.e., sensing devices with
the same properties. In SensorML, a sensor array defines
a set of devices of the same type at different locations,
whereby a sensor group describes several sensors that
operate together to provide one collective observation.
• Observations & Measurements (O&M)
This is the counterpart to SensorML in the field of the
actual study of phenomena. That is, it provides a
description of sensor observations and measurements in
the form of general models and XML encodings. The
term observation is defined as “an action with a result
which has a value describing some phenomenon“. The
O&M standard labels several terms for the measurements
themselves, as well as for the relationship
between them, whereby the extent is limited to measurement
results, which are expressed as quantities,
categories, temporal or geometrical values, as well as
arrays or composites of these. Naturally, the monitored
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values normally require a reference system to enable a
meaningful interpretation and further processing by providing
a context for the results [81].
It shall be stated that despite OGC’s tendency towards
using the geographical position as the central and connecting
element in geospatial standards, the location
parameter is considered a regular measurement within
O&M. This means that the position is equipollent with
other measurands such as time, air temperature or satellite
images.
• Transducer Model Language (TML)
Generally speaking, TML can be understood as O&M’s
pendant or streaming data by providing a method and
message format describing how to interpret raw transducer
data.
• Sensor Observation Service (SOS)
This component provides a service to retrieve measurement
results from a sensor or a sensor network. In
other words, the SOS groups a collection of possibly
heterogeneous sensors, as illustrated in Figure 4[82],
and provides their measurements via a standardised service
interface.
The SOS specification defines the operations offered
by a specific sensor, whereat the minimum collection of
methods comprises GetCapabilites, DescribeSensor and
GetObservation, which return information about the
observations and measurements supported by the SOS.
The kinds of data provided by a sensor and the sensor
types themselves can be fetched from a sensor registry.
SOS references the O&M specification for encoding sensor
observations, and the TransducerML and SensorML
specifications for modelling sensors and sensor systems.
• Sensor Planning Service (SPS)
This component provides a standardised interface for
collection assets and aims at automating complex information
flows in large networks. This requires the support
of various capabilities, as well as different request
processing systems, as described below.
The OGC recommendation defines interfaces for
requesting information containing the capabilities of a
SPS, for retrieving the practicability of a sensor planning
request, for determining the status of such a request, as
well as for submitting, updating or cancelling a sensor
planning request [83].
Thus, SPS can be seen as the implementation of a bidirectional
communication between a client and the
sensor network. The client can send instructions to the
network, which can be triggered by different kinds of
events. One possibility is that a system administrator
instructs the sensor network to send measurement
values every five minutes instead of every hour in case a
water level threshold is exceeded. Another commonly
used sample functionality is the control of a remote
camera to change orientation or focus.
Figure 4 SOS (Sensor Observation Service) general architecture (adapted from [82]).
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• Sensor Alert Service (SAS)
The OGC SAS specifies interfaces (not a service in the
traditional sense) enabling sensors to advertise and publish
alerts, including according metadata. SAS can be
used by clients to subscribe for sensor data alerts with
some spatial and property-based constraints. Also, sensors
can be advertised to the SAS allowing clients to
subscribe for the sensor data via the SAS. SAS, which is
currently in its version 0.9.0, is not released as an official
OGC standard [84].
In the SAS context, ‘alerts’ are not only understood in
the classic meaning of the word, i.e., an automatic signal
or notification indicating that an event has fired (e.g., a
message in case of threshold exceedance), but in a
broader context. Alerts are defined as ‘data’ sent from
the SAS to the client, which may as well comprise
alerts/notifications (e.g., OGC Web Notification Service
(WNS)) as observational data (measurements matching
pre-defined criteria).
SAS uses the Extensible Messaging and Presence Protocol
(XMPP) for the delivery of sensor notifications.
Thus, SAS leverages an XMPP server, which can be
embedded directly in the SAS or act as a separate service.
SAS notifications are provided via a Multi User
Chat (MUC) for each registered sensor. To receive notifications,
a client has to join the specific MUC.
• Web Notification Service (WNS)
The last part of the SWE model is the Web Notification
Service (WNS), which is a service enabling a client to
perform asynchronous dialogues, that is message
exchanges, with other services. This process is especially
expedient when several services are required to comply
with a client’s request, or when an according response is
only possible under considerable delays.
Principally, the service comprises two kinds of communications,
the one-way-communication and the twoway-communication.
The former, also known as simple
WNS, for which users have to be registered, can be realised
via the transmission of messages over e-mail,
HTTP (Hypertext Transfer Protocol), Short Message
Service (SMS), instant messaging, telephone, letter or
fax. The latter system, viz extended WNS, is able to
receive user notification responses [85].
Furthermore, sensor Web registries play an important
role in sensor network infrastructures. However, they
are not decidedly part of SWE, as the legacy OGC Catalogue
Service for Web (CSW) is used.
The registry serves to maintain metadata about sensors
and their observations. In short, it contains information
including sensor location, which phenomena they measure,
and whether they are static or mobile. Currently,
the OGC is pursuing a harmonisation approach to integrate
the existing CSW into SWE by building profiles in
ebRIM/ebXML (e-business Registry Information Model).
Summarising, SWE aims at enabling the discovery and
querying of sensor systems, observations, and observation
procedures over the Internet. This process comprises
determination of a sensor’s capabilities and
quality of measurements, access to sensor parameters
that automatically allow software to process and geolocate
observations, retrieval of real-time or time-series
observations and coverages in standard encodings, tasking
of sensors to acquire observations of interest, and
subscription to, and publishing of, alerts to be issued by
sensors or sensor services based upon pre-defined
criteria.
The OGC is developing SWE in tight coordination
with other geospatial standards for data representation,
provision and processing. This enables simple integration
of sensor networks into existing Spatial Data Infrastructures
(SDI) and data analysis systems by providing
standardised service interfaces and APIs (Advanced Programming
Interfaces). This development is of particular
importance for achieving the far-reaching vision of ‘citizens
as sensors’ in time-critical scenarios, such as emergency
management and public health monitoring.
The OGC Open GeoSMS is developed by ITRI
(Industrial Technology Research Institute, Taiwan) for
exchanging location information via the common mobile
service, SMS [33,86]. Open GeoSMS can be composed
with a mobile phone application, by retrieving GPS data
and then embedding the geo-location coordinates in an
SMS message. An example of an Open GeoSMS message
is shown in Figure 5.
For an SMS notification to be compliant with the
Open GeoSMS specification, the following criteria have
to be fulfilled:
1. The first line of the SMS has to be a URL (Uniform
Resource Locator)–see top of Figure 5;
2. This URL has × and y coordinates as the first two
parameters;
3. This URL ends with ‘&GeoSMS’; and
4. Optional text can be appended for further description,
e.g., of an (emergency) event at the specified geolocation
and/or sensor readings at that location.
Mobile phones can be classified into three types for
Open GeoSMS purposes:
• A feature phone that allows no application to be
installed: Because this is an SMS message, almost every
mobile phone can receive Open GeoSMS notifications similar
to the one shown in Figure 5. The notifications are also
readable by humans and users can easily understand that it
is a CO2 level alert (to use the same example in Figure 5);
• An online smartphone: In the example presented in
Figure 5, the user can simply click on the URL to access
Google Maps service. The URL in Open GeoSMS can
point to any given service provider (i.e., not necessarily
Google Maps), so various kinds of information and
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services can be accessed via this URL. Of course, the
application on the phone can also parse every incoming
SMS, and once an Open GeoSMS is detected, coordinates
are retrieved and further action, such as raising a
warning or Standard Operation Procedure (SOP), is triggered;
and
• An offline smartphone: Because the application on
the phone can parse and get the coordinates in the
Figure 5 Smartphone displaying details of an Open GeoSMS notification and incident location on Google Maps.
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Open GeoSMS message, offline maps such as OpenStreetMap
[87] can be used to display the sent (incident)
location, for those users who do not or cannot
have data (Internet) access.
By overlaying the message text (incident details) on
the map (Figure 5), Open GeoSMS presents clear information
to users, including both geo-location and sensor
information. Open GeoSMS can prove extremely helpful
in public health emergency notification and management
operations, since it works on almost any kind of
mobile phone supporting SMS. It is an open standard
that aims at enabling interoperability among different
platforms. Figure 6 shows how Open GeoSMS has been
implemented in Ushahidi [14] and in Sahana Disaster
Management System [34] for incident reporting in
emergency and disaster management operations. People
reporting an incident can (still) make an ordinary phone
call or send a conventional SMS message to the emergency
services handling such situations, but with Open
GeoSMS, geo-tagged SMS reports can significantly
shorten the processing time for incident reports (and
possibly save more lives by doing so). Open GeoSMS
can also be used for task assigning and dispatching during
disaster management operations (see bottom half of
Figure 6).
Common Scents - mobile pervasive sensing using bicyclemounted
sensors
The Common Scents project aims at providing finegrained
air quality data to allow citizens and urban decision-makers
to assess environmental conditions instantaneously
and intuitively. The goal is to provide realtime
information on urban processes to support shortterm
decisions at multiple levels, from personal to governmental.
To achieve this goal, the SENSEable City
Laboratory at the Massachusetts Institute of Technology,
USA, built up a mobile sensor network of bicyclemounted
environmental sensors to realise the vision of
‘citizens as sensors’.
Within the Common Scents project the term ‘realtime’
is not defined by a pre-set numerical time information,
but layers have to be created in a timely manner
to serve application-specific purposes. For instance, an
update on traffic conditions does not have to exceed a
delay of a couple of minutes when this information is
used for navigation instructions, whereas a 30-minute
update interval can well be sufficient for short-term trip
planning.
The Common Scents system architecture is based on
the Live Geography infrastructure [88], which proposes
a portable and open-standards-based monitoring infrastructure,
including components for sensor data provision,
sensor fusion, real-time data analysis, and usertailored
information visualisation. The approach
accounts for different design principles such as Service
Oriented Architectures - SOA, modular software infrastructures,
and component-based development. This
ensures flexibility, reusability and portability of the components
and the overall infrastructure. Figure 7 shows
the monitoring architecture and the standardised service
interfaces that are used to connect the different components
in the workflow of the Common Scents
implementation.
According to principles of SOA and sustainable infrastructure
development, a data collection, processing and
information provision architecture was conceived and
implemented, covering the whole process chain from
sensor network development via measurement integration
to data analysis and information visualisation, as
shown in Figure 7. Hence, this infrastructure can potentially
serve as the architectural bridge between domainindependent
sensor network developments and use case
specific requirements for end user tailored information
output for public health monitoring.
The modules of the workflow shown in Figure 7 are
separated by several interfaces, which are defined using
open standards. These primarily include the Sensor
Web Enablement (SWE) initiative that aims to make
sensors discoverable, query-able, and controllable over
the Internet, as described elsewhere in this article.
Real-time air quality analysis using mobile bicyclemounted
sensors: One pilot experiment in the Common
Scents project was conducted in the city of Copenhagen,
Denmark. Ten bicycle mounted sensors were deployed
as a mobile sensor network to collect environmental
data together with time and the geographic location,
velocity and acceleration using GPS. In this experiment
of ubiquitous mobile sensing, the Sensaris City Senspod
(Figure 8) has been used, a relatively low-cost sensor
pod. The deployment in Copenhagen was a combined
effort of the MIT SENSEable City Laboratory and
Københavns Kommune, Denmark.
The Sensaris City Senspod is a sensing device for
environmental parameters that is dedicatedly designed
for use in urban environments [89]. It collects CO,
NOx, noise, air temperature and relative humidity,
together with the geographic position and time via GPS.
The City Senspod has proven to be a good choice for
pervasive sensing because of its relatively low price and
acceptable measurement accuracy. However, the City
Senspod shows a few drawbacks including a minimum
operational temperature of 5°C and its communication
via Bluetooth, which is not the optimum transmission
technology when aiming for maximum energy efficiency
in the context of pervasive monitoring.
To comply with the standardised infrastructure of
Common Scents system architecture, several standardised
services were implemented on top of the sensor
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network, in accordance with the Live Geography
approach. For data access, a Sensor Observation Service
(SOS) was developed to supply measurement data in the
standardised O&M format. It builds the O&M XML
structure dynamically according to measured parameters
and filter operations. To generate alerts, e.g., in case of
exceedance of a threshold, an XMPP (Extensible Messaging
and Presence Protocol)-based Sensor Alert Service
(SAS) was implemented. It is able to detect patterns and
anomalies in the measurement data and generate alerts
Figure 6 Open GeoSMS is used in Ushahidi and in Sahana Disaster Management System.
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and trigger appropriate operations such as sending out
an email or a text message, or to start a pre-defined GIS
analysis operation.
The pilot deployment itself has been carried out in the
course of the Copenhagen Wheel project, which has
been initiated by the MIT SENSEable City Lab [24,90].
This project was officially presented in Copenhagen on
15 December 2009 in the course of the 15th
Conference
of the Parties during the 2009 United Nations Climate
Change Conference meeting. The Copenhagen Wheel is
a specially designed bicycle to capture energy dissipated
while cycling and braking, to store it in an in-wheel battery
and support the cyclist on demand through a small
electrical engine.
In the Common Scents project, Sensaris City Senspods
have been attached to the bicycles, capturing information
about carbon monoxide (CO), NOx (NO + NO2),
noise, ambient temperature, relative humidity, in addition
to position, velocity and acceleration. The environmental
sensors were originally intended to be placed
within the hub of the bicycle wheel; however due to
logistical pressure, they were placed on bicycles ridden
by couriers in Copenhagen going about their normal
daily routine. Ten cycles were instrumented and tested
over 2 December 2009. It is believed that this was the
first time multiple mobile sensors had been used in the
field with such a large variety of environmental sensors
on a city-wide scope.
Figure 7 Common Scents technical architecture. WFS: Web Feature Service; WMS: Web Map Service; WCS: Web Coverage Service.
Figure 8 Sensaris City Senspod.
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The analysis component, which processes the collected
data, performs a spatial Inverse Distance Weighting
(IDW) interpolation on temperature measurements,
which will be used in further research efforts for correlation
operations with emission distribution or traffic
emergence, and for the detection of urban heat islands.
It has to be stated that IDW is presumably not an optimised
algorithm for drawing conclusions from point
measurements to a city-wide scale. In a future effort, an
accurate urban dispersion model will be integrated into
the analysis.
In the field trial, the processing module analyses the
CO, NOx, noise temperature and relative humidity distributions
throughout the city of Copenhagen. The CO
map containing the GPS traces, which figuratively redraw
the urban street network, is shown in Figure 9. A
first qualitative analysis of the mobile measurements
shows that there are strong correlations between ambient
temperature, CO and NOx values. Further preliminary
outcomes show that both CO and CO2 are
undergoing very high temporal and spatial fluctuations,
which are induced by a variety of factors including temperature
variability, urban topography, time during the
day, the ‘urban canyon’ effect, traffic emergence or
‘plant respiration’ - the fact that plants release major
amounts of CO2 overnight.
Future research will include the investigation of direct
correlations between pollutants, environmental measurements
and traffic emergency. It is well known that CO
is a measure of the efficiency of combustion in vehicles
that may be used to reflect changing driving patterns
and the sensitivity of air quality to larger scale environmental
features such as wind speeds over the city. However,
the detailed interplay of these parameters still has
to be investigated in a next step. Especially CO values
measured in the Copenhagen pilot have to be normalised
over humidity and temperature to perform further
quantitative (absolute amounts) and qualitative (impact
on public health) analysis.
Concluding, it can be stated that the Copenhagen
experiment was an important step toward the realisation
of pervasive monitoring by the use of mobile sensors.
Figure 9 Mobile CO measurements in the city of Copenhagen (December 2009).
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Particularly, it has been shown that the vision of ‘citizens
as sensors’ for environmental monitoring and public
health is technically and methodologically feasible.
LSM (Linked Sensor Middleware) - a geosemantic sensor
mashup
Linked Stream Middleware (LSM) [26], a platform
developed at the Digital Enterprise Research Institute
(DERI) at National University of Ireland Galway, Ireland,
that brings together the live real world sensed data and
the Semantic Web [91] in a unified model is an example
of a large scale sensor platform that if combined with
Social Web data could provide a comprehensive insight
into the domain of citizen sensor data. A sample LSM
deployment is available at [25] and currently displays
data from over 100,000 sensors around the world (Figure
1). The interface uses a map overlay to query and
display sensor information. Several types of sensor data
are available, such as flight status, weather, train/bus
arrival times, street cameras, sea level monitors, etc. The
history of the data produced by a particular source is
available and downloadable in Resource Description Framework
(RDF) format [92].
The LSM architecture, as shown in Figure 10, is
divided into four layers. The Data Acquisition Layer
provides three wrapper types: Physical Wrappers that
are designed for collecting sensor data from physical
devices; Linked Data (LD) Wrappers that expose relational
database sensor data into RDF; and Mediate
Wrappers, which allow for collection of data from other
sensor middleware such as Global Sensor Networks
(GSN) [93], Pachube [94], and the sensor gateway/Web
services from National Oceanic and Atmospheric
Administration (NOAA) [95]. The Linked Data Layer
allows access to the Linked Sensor Data created by the
wrappers but links to the Linking Data cloud (a subset
of the Linking Open Data cloud [96] shown in Figure
11). The Data Access Layer provides two query processors,
a Linked Data query processor and the Continuous
Query Evaluation over Linked Streams (CQELS) engine
[97], and exposes the data for end-users or machineusers.
The fourth layer, the Application Layer, offers a
SPARQL (SPARQL Protocol and RDF Query Language)
[98] endpoint, a mashup [99] composer, linked sensor
explorer, and streaming channels [92].
The LSM system is of interest in the area of citizen
sensing because it implements an architecture that
could be used for large-scale citizen sensing projects. As
mentioned before, over 100,000 sources are available to
the current running implementation of LSM. Scalability
and reliability are important factors when designing any
system; but when collecting real-time stream data (i.e.,
from Twitter and other social media feeds or from sensor
feeds), uptime of a system becomes critical and so
does its graceful scaling up to process the data in realtime.
Transforming the sensor data into a standard format
such as RDF also allows for standard sensor
descriptions using the SSN ontology as described earlier.
Some research in the area of citizen sensing has tried to
leverage the power of the SSN ontology to describe sensors
on mobile devices for rural transportation projects
[100] and in emergency reporting applications on microblogging
platforms [101].
Annotating microblog posts with sensor data could
add context and remove some of the ambiguity of the
short SMS-style languages commonly used on microblogging
systems and could aid the processing of these
texts for information extraction using natural language
processing. (The concepts of annotations and machinereadable
metadata that “travel” with a tweet (without
using any of the 140 characters that are reserved for the
tweet text message) were the basis of the not-yetreleased
(as of Q4 2011) ‘Twitter Annotations’ feature
[102] and related work by Bottlenose [103], and are
similar to the way ‘Twitter Places’ [104] currently adds
geo-location context to tweets.) Sensor data annotations
would add to the semantic annotation described by
Sheth [64] and aid in analysis and dissemination of
information.
3D Town Project - three-dimensionalisation of indoor and
outdoor surveillance networks
In recent years, urban ICT (Information and Communication
Technology), (such as mobile and wireless communication
technologies and the Internet, ubiquitous
sensing and computing, digital media and urban
screens), has been rapidly modifying city life. The ‘augmented
city’ is a modern definition of urban spaces,
where no discernible boundaries exist between “virtual”
and “physical” spaces [105]. The “virtual” urban space is
a digital environment where the urban ICT is connected
to “physical” urban space. The “virtual” urban space is
often represented by three-dimensional (3-D) cityscape
models. These 3-D city models are virtual representations
of the “physical” urban spaces that digitally reproduce
all the urban objects with a semantically enriched
polyhedral world. Human beings’ physical-digital intersection
exists through the awareness of their location
(sense of belonging to place) on the global level, but
also on a very local scale. This location awareness does
not only mean having knowledge of ‘where we are’, but
also the ability to perceive or to be conscious of objects,
events and patterns of surrounding environments with
respect to ‘where we are’.
Today’s most representative augmented city examples
are the GeoWeb portals such as Google Earth and
Microsoft Bing Maps [106] that integrate location-based
geographical information with an extremely broad range
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of non-spatial information through Web technology.
Three-dimensional city models are a crucial extension
of the GeoWeb since they provide an enriching, interactive,
and visually appealing user experience that is “in
tune” with users’ natural visual-based thinking, imagination
and space perception. Due to their many potential
benefits in various domains, there has been a rapidly
increasing demand for GeoWeb applications. Today’s
GeoWeb, however, is only visualising a static virtual
world, which limits its use in applications where having
knowledge of object dynamics/real-time motion is
important. Our cities are dynamic, living environments
with various kinds of real-time information and urban
objects (people and vehicles) moving around us every
day. To bring such dynamic information into the GeoWeb
will give users a more immersive context to feel
and interpret a real dynamic world.
A research team at York University, Canada, has been
investigating and developing ‘3D Town’, a research project
that focuses on the development of an augmented
city for sensing, distributing, interpreting and visualising
the real-time dynamics of urban life. A core idea of the
project is to integrate temporal information such as the
movement of pedestrians and cars obtained using surveillance
video with 3-D city models and thus implement
a location-based awareness and means of
interacting with 3-D city models through moving
objects. To achieve this goal, the research team has
implemented a dynamic GeoWeb (’D-GeoWeb’) system
that enables the management of [107]:
• Real-time data acquisition of wireless sensors distributed
in indoor environment (sensor layers);
• Data protocols to integrate SensorML, IndoorML
[108] and CityGML [109] (protocol layers);
• Data management layers to handle indoor and outdoor
3-D models and associate semantics, real-time sensor
and moving object information (data layers); and
• Dynamic response to and rendering of requests by
tracked moving objects (responsive layers).
A schematic of data flow in D-GeoWeb is shown in
Figure 12. To avoid labour-centric processing bottlenecks,
a new method has been investigated to integrate
indoor and outdoor models using geometric hashing
algorithm [110]. The proposed method aims to integrate
Figure 10 Layered architecture of the LSM (Linked Sensor Middleware) platform. ‘RESTful’ refers to conformance to REST (REpresentational
State Transfer) constraints.
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2-D floor plans with terrestrial laser scanning data in an
automatic manner. Thus, a fully integrated 3-D building
model was reconstructed to create a seamless outdoor
and indoor navigation database. New object detection
and motion tracking algorithms were developed to
detect, classify and track people and cars using pan/tilt
video sequences [111]. ‘3D Town’ is able to co-register
indoor and outdoor wireframes with surveillance videos
in a combination of vanishing point detection and line
matching between wireframes and line segments
detected from the image frames. In addition, a vision
algorithm was implemented to track and recognise moving
objects from surveillance videos. Finally, detected
moving objects were localised and rendered in 3-D
models as a sprite on a real-time basis. A prototype
Web-based system was developed based on Google
Earth Plug-in [112] to visualise the dynamic information
and provide an interface between the users and the
dynamic virtual 3-D world (but a WebGL [113] implementation
would have been ideal, for plugin-free Web
browser access of the dynamic 3-D virtual globe, e.g.,
[114,115]).
The 3D Town research shows promising results and
demonstrates the feasibility of integrating dynamics and
movements detected from sensors and videos with a
corresponding 3-D virtual world. Figure 13 demonstrates
3D Town’s capability of tracking people, who
walk in a hallway, using surveillance video (upper-right
inset) and localising them with 3-D sprites in Google
Earth. A balloon shows a communication (room’s occupancy
and temperature information) between the virtual
sprite and Crossbow wireless sensor [116], which pops
up when the sprite stops at a room. Figure 14 presents
results of tracking buses and pedestrians using surveillance
camera under outdoor circumstances, which are
again localised with 3-D sprites in Google Earth.
PIEs - Precision Information Environments for emergency
management
The first decade of the 21st
century saw a range of disasters
strike worldwide, including terrorist attacks, hurricanes,
tsunamis, wildfires, earthquakes, and a
pandemic. The immediate and far reaching impacts of
these disasters highlight the need for rapid and effective
emergency management. The immense tragedy, uncertainty,
and fear generated by an emergency underscore
the necessity for effective regional preparation, response,
recovery, and restoration.
Figure 11 ’Linking Open Data’ datasets as of September 2011. Linking Open Data cloud diagram by Richard Cyganiak and Anja Jentzsch. A
version of the same diagram with clickable hyperlinks is available at [95].
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Figure 12 Dynamic GeoWeb server. KML: Keyhole Markup Language; KMZ: zipped KML; PHP: Hypertext Preprocessor (a server-side scripting
language); SQL: Structured Query Language.
Figure 13 3D Town indoor tracking and location intelligence: video from surveillance camera (upper-right inset). The results of tracking
people are visualised using 3-D sprites. Wireless sensor data are dynamically read as the sprite accesses them.
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For emergency management personnel to make accurate
and timely decisions, they must have situational
awareness, an accurate perception of the situation that
they are facing and its complex data-scape. Essential to
good situational awareness is the ability to provide relevant
and timely information to decision makers and the
public. Effective information collection and sharing has
long been recognised as a challenge in emergency management
[117].
These issues are growing more difficult with the adoption
of social media as a pervasive way to share and disseminate
information. The public is rapidly becoming the
first reporter in the field to capture and disseminate information
about an event as it occurs. Emergency management
personnel increasingly need to leverage social media
for situational awareness and information sharing. However,
the volume, potential for anonymity, and lack of context
can make information derived from social media hard
to trust, and its intent and origin hard to discover.
As a point of reference for data volumes in social
media (the ‘problem space’), in just one hour Facebook
[118] has 5,553,000+ status updates, 30,624,000 comments
and 8,148,000 photos (statistics as of January
2011) [119]. In the same hour, Twitter has about
10,416,000 new tweets (statistics as of October 2011)
[120], Flickr has 180,000 new photos (statistics as of
September 2010) [121] and YouTube has another 2880hour
worth of video (statistics as of 2011) [122]. This is
an information rich society and one where anyone can
publish or broadcast. All of this information can be
leveraged for situational awareness in an emergency, but
no one user or group can digest it all.
The fast pace and critical nature of emergency management
requires the ability to access and share
information efficiently and effectively. Personnel often
have difficulties obtaining the information they need for
an effective response, and they frequently find that
information is not shared across organisations. With the
addition of social media as another input, there is often
more information available than can be understood at
the pace needed (information overload - cf. the notion
of the Social Web “firehose”). To address this challenge,
mechanisms must be put in place to assure that personnel
always have awareness of, and trust in, the information
relevant to their current role and activity.
Researchers at Pacific Northwest National Laboratory
(PNNL) are developing future work environments
(situation rooms) for the emergency management community
that enable high-volume data feeds, including
social media, to be processed and analysed such that
participants in a response activity receive tailored data
relevant just to their needs and roles. These Precision
Information Environments (or PIEs) provide tailored
access to information from disparate sources augmented
with decision support capabilities in a system that is
designed around the multiple user roles, contexts, and
phases of emergency management, planning, and
response. A Precision Information Environment provides
visual analytic [123] capabilities through novel
interactions that transform the way emergency professionals
- from first responders to policy makers - engage
with each other and with information. To develop the
requirements for these environments, PNNL adopted a
user-centred design philosophy in which emergency
management personnel are involved in all aspects of the
research from requirements definition, to scenario and
use case development, constructing a capability vision,
and feature development. The research team performed
Figure 14 3D Town outdoor moving object tracking and recognition: video from surveillance camera (bottom-right inset).
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over fifty interviews, contextual inquiries and ethnographic
studies to better understand the emergency
management community and document the gaps and
opportunities in the space. This work led to a scenariodriven
vision articulated through a research agenda and
video [29,30].
This vision video (Figure 15), designed around a wildfire
scenario 8-10 years into the future has become a
north star for development, stakeholder outreach and
user feedback. The vision for PIEs integrates data modelling
and visual analysis, real-time and historical data
streams, and novel user interface concepts in an
approachable, easy to use collaborative application.
Information and visual interfaces are tailored to the specific
roles and tasks of each user. The goal is real-time
synthesis, communication, and analysis of dynamically
generated and collected information, all of which provides
for sound decision making. PIEs allow users to
engage with each other and leverage their collective
expertise and experience in an environment combining
virtual worlds based on actual physical models, realtime,
multimodal data streams, and sophisticated visualisation
tools to support actions, assessments, and decision-making
(cf. vision in [27]).
Global profile, dynamic reputation and trust
Reputation and trust, both of emergency management
personnel and members of the public that provide data,
are equally important. Emergency management personnel
often form ad hoc teams or networks during an
event in which not all parties or individuals are known
to each other. Emergency managers must also often rely
on third party public reporting to assess the situation
before responders are dispatched to the scene. In some
cases, as in a natural disaster, an event can be so large
and remote that professional assessment is not possible
(in a timely manner). In those cases, profile and source
assessment is just as important as the situation. Is the
source trustworthy? Is there prior experience to suggest
how useful a source’s input is likely to be?
The global profile system inside a Precision Information
Environment is applied to emergency management
professionals and PIE content sources such as government
professionals, nongovernmental organisations, private
industry, and citizens. Each type of source is
assigned a reputation score that is adapted over time
based on the content they create (and how it is used by
others) and the people they interact with. Emergency
management professionals and responders may initially
receive the highest reputation score followed by other
government professionals that use or could use the
environment. Other sources of content may initially
have less trust associated with the data they provide, but
their reputation score can increase based on other users’
rating of their contributions.
The system also allows for source tracking and measuring
the effectiveness of a message. It can also track a
message as it changes or distorts through the social network,
allowing emergency management to isolate when
a message deteriorates. They can then reinforce the
message through the social network by releasing an
update to answer new questions and theories as they
arise.
Tailored information services and adaptive data triage
At the centre of the Precision Information Environment
is a profile for each user that defines the user’s information
interests and needs. One’s role in an emergency
event is a core part of this profile, and the PIE system
uses roles defined by the National Incident Management
System of the US Federal Emergency Management
Agency to provide an initial template for information
interest. Role-driven tailored information services and
adaptive data triage bring ‘Precision’ into a Precision
Information Environment. They allow an emergency
manager to get exactly the right information at the right
time and avoid information overload by filtering data to
only those which are likely to be most relevant to a
given user. In this way, the user can stay focused on the
tasks and activities that matter.
Figure 15 Spatially-enabled elements of the Precision Information Environments (PIEs) vision. From left: collaborative modelling and
decision making, natural user interactions, and role- and task-driven information and map displays that synthesise large amounts of
heterogeneous data about an event into a user-specific display.
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PNNL’s approach to information triage relies on a
“signature” for each user that defines the terms that
they are interested in and the relative weight of each
term. As new data arrive from social media and other
sources, a similar signature is constructed for each new
data item. By comparing user and item signatures, we
can determine which items are most relevant to which
users. The initial recommendations made by the PIE
system are tuneable by the user, so that as the situation
changes so can his or her environment. Data are filtered
and sorted based on the relevancy score for each user.
This makes precision possible and allows the user to
focus on content that is personally of interest to him/
her based on his/her current activity. As the user works,
communicates and shares information, he/she can train
the system about his/her interests by simply ‘voting’ on
whether or not each object is of interest to him/her
(Figure 16). If an object is interesting, then those signatures
get added to the user’s profile (or weights
increased if already in the profile). If it is not relevant,
the ranking of the signatures gets diminished and gets a
lower relevancy score.
PNNL uses a technique called ‘tailored information
services’ to provide relevance-ranked data to every component
of a PIE system. In addition to managing data
ingest and triage, PIE tools can support creation and
tracking of tasks in emergency response. All events,
including data and tasks, are passed through the core
PIE relevance engine, so that all information, regardless
of source, can be accessed through a middle layer that
performs per-user triage.
Collaborative natural user interfaces
In addition to data overload, there can be ‘software (user
interface) overload’ in the emergency management community.
Emergency management personnel are inundated
with many different applications, each of them
potentially specialised to activities that are only exercised
during an emergency. As a result, they have to
learn or retrain to use the software when an emergency
occurs, which hinders adoption and use of new technology.
The community is also highly mobile and is frequently
marked by movement between user
environments, such as from the desktop, to a collaborative
setting, to the field. As a result, interfaces to data
analysis and collaboration systems must be consistent
across these platforms to minimise the learning curve.
A Natural User Interface (NUI) refers to a user interface
that feels invisible, or becomes invisible with successive
learned interactions, to its users. These
interfaces are “natural” because the interactions they use
are intuitive in their consistency with actions people
already use outside of computer interfaces, e.g., touch,
gesture and voice [124]. PIEs use NUI principles to
allow users, especially those unfamiliar with a new
Figure 16 PIEs user profile and signature ranking system showing term relevance. At the centre of the display is a mapping between
prioritised concepts in a user’s profile (right) and concepts aggregated across all users’ profiles (left).
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system, to learn how to extract value from an information
display quickly, and to create a desirable and engaging
user experience.
PNNL is also actively researching and prototyping new
video teleconferencing devices that are designed to be
‘always on’ and support ad hoc meeting and information
discovery among geographically distributed teams. LiveWall
(Figure 17) is a prototype that supports high-definition,
full-size video overlaid with an adaptable
transparent information layer that gives the user the
feeling of looking through a digital glass panel into
another room. LiveWall uses a multitouch interface to
allow distributed teams to interact with data and engage
in collaborative decision making in a manner very similar
to how the team would work if it were co-located
and discussing a shared display (such as a printed map)
in front of them.
Discussion and conclusions
Increasing numbers of gadgets and appliances, including
medical and hospital diagnostic devices, are now
Internet-connected or embedding M2M SIM cards/
GSM (Global System for Mobile Communications/
Groupe Spécial Mobile) modules to allow reporting
data to backend systems for diagnostic, telemetry and
control purposes, and to gain useful insights about the
populations using such devices. While it is possible to
track and monitor the behaviour of crowds of people
without even letting them know that they are being
watched, e.g., tracking population movements using
mobile phone network data (SIM card movements)
during disasters and outbreaks [125,126], analysing
aggregates of data generated during patient visits to
clinics/hospitals, diagnostic laboratories and pharmacies
[127], or using Internet search engine analytics
[128-130] (though the latter method should always be
interpreted with a grain of salt, as it might not work
equally well for all conditions, the findings might not
always be accurate [131], and search engine query
words and phrases tend to lack a clear and complete
context attached to them and to be less “expressive”
than other forms of textual expression using social
media), the real power and uniqueness of crowdsourcing
lies in the active participation of intelligent
humans in a task assigned to them. People, as social
beings, have always shared information and helped one
another in various situations; social media and crowdsourcing
capitalise on this fact and enable us to share
and support more (both in quantity and frequency,
more content, more often), with many more people
and much more quickly. Kamel Boulos’ 2005 phraseterm
‘wikification of GIS by the masses’ [1] conveys
this meaning by comparing the process to that of collaboratively
editing a wiki such as Wikipedia [132] by
a distributed network of a large number of intelligent
human editors, where the power of darwikinism [76]
comes into play. Volunteer citizens acting in groups
(crowds) and sharing communication horizontally (in
addition to vertically ‘up’ and ‘down’, as necessary) are
challenging the notion that rapid information flow
‘upwards’ provides the optimal configuration. Information
shared horizontally has been shown to be:
• More timely, as there is a peer pressure to help
equals;
Figure 17 LiveWall prototype in use during a usability study at PNNL.
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• More complete, as there is transparency in the
reporting;
• Higher in quality (in terms of sensitivity), as local
populations know what is the baseline behaviour of
their own communities; and also as peers sensitise each
other to be on the look for certain ‘signals’ (for example,
one volunteer reports high numbers of children absent
from schools, prompting others in the network to ask
the same question in their vicinity); and
• Higher in quality (in terms of specificity), as being
local allows to quickly validate, verify information, and
dismiss false positives earlier (cross-validation and verification
by peers).
The technologies supporting ‘citizens as sensors’ have
to be:
• Horizontal, allowing citizens to share information
with each other, in addition to vertically with situation
rooms and similar centres (e.g., Amazon’s Price Check
comparison-shopping app [133] allows sharing in-store
prices vertically with Amazon, as well as horizontally
with other customers via Twitter, Facebook and text
messages, in addition to accessing other customers’ product
reviews);
• Semi-structured, allowing people to report what they
deem relevant, not restricting them to very tightly structured
forms and templates;
• Real-time, as information has to flow back and forth
in real-time allowing the creation of dialogue;
• Open, whereby members of a group have to feel they
can add to the conversation or reporting task other people
who can provide value, thus creating a meritocracy
and allowing the crowdsourced community to grow
while factoring ‘credentials, reputation and trust’ into
the process;
• Geo-aware, noting that local citizens have a high
authority on what is nearby to them; having this piece
of information is essential for the contextualisation and
interpretation of data; and
• Accessible, meaning that the process can also work
on even the simplest mobile phone, for example using
SMS text messages (cf. GeoSMS).
The presence of multimodal sensors on more
advanced smartphones and tablets carried by citizens is
also enabling a broad range of possibilities, but the automatic
collection of detailed sensor data from mobile
devices may compromise user privacy and this has to be
adequately addressed in mobile participatory sensing
applications relying on such data [134]. In an editorial
for a 2008 special issue of GeoJournal on citizen-contributed
geographic information, Elwood raises some of
the more sociological issues regarding crowd-enabled
technologies that are equally worth considering [135].
The counterpart of crowdsourcing is ‘crowdreaching’,
which involves reaching out to people with various
messages, e.g., ‘health tips’, especially at times of mass
stress [75], and capitalising on the viral and ubiquitous
natures of mobile and social media to do so (cyberinfluence).
Consumers and citizens might also be willing to
pay for useful and individualised information. Services
that provide health tips can thus be commercially viable
(if not funded by government/public health authorities
or similar bodies), in addition to being a direct source
of self-reported health information. For example, using
tools such as InSTEDD RemindEm [136] (free and open
source), pregnant citizens can subscribe to health tips
for their current stage of pregnancy by texting in their
LMP (Last Menstrual Period); location-tailored tips for
diabetics, pre-operatory or post-operatory guidelines,
etc. can also be served using RemindEm. Platforms that
offer some crowdreaching value and crowdsharing
opportunities to citizens reporting their health conditions
(while adequately protecting users’ privacy) such
as PatientsLikeMe [137] allow the creation of crowdsourced
aggregated datasets that shed light on specific
populations, diseases and geographies with regards to
health.
For cross-border health surveillance, where neighbouring
towns/cities and countries affect each other’s health
but might be very ‘distant’ in terms of the bureaucratic
processes required to share information in a timely
manner (even when all essential data sharing agreements
are in place [138]), tools are needed that respect each
jurisdiction’s need for controlling access to its crowdsourced
(expert) reports and data, while providing
mechanisms for sharing adequate situational awareness
of health events in sentinel border sites. Some of this
functionality is available in Veegilo [139], a simple open
source tool that aggregates disease indicator numbers
from national databases into a common space where
incidence and reported deaths of monitored diseases
can be seen and compared across sentinel sites and over
time. Its primary use has been for international health
networks, but can also be applied at national or provincial
level to simplify data entry.
In this paper, we presented a comprehensive state-ofthe-art
review of the overlapping domains of the Sensor
Web, citizen sensing and ‘human-in-the-loop sensing’ in
the era of the Mobile and Social Web, and the roles
these domains can play in environmental and public
health surveillance and crisis/disaster informatics. We
covered the key issues and trends in these areas, the
challenges faced when reasoning and making decisions
with real-time crowdsourced data (such as issues of
information overload, “noise”, misinformation, bias and
trust), the core technologies and Open Geospatial Consortium
(OGC) standards involved (Sensor Web Enablement
and Open GeoSMS), as well as a few outstanding
project implementation examples from around the
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world (Common Scents/the Copenhagen Wheel, Linked
Sensor Middleware, 3D Town, and Precision Information
Environments).
Acknowledgements
BR would like to thank Rex Britter and Christine Outram, as well as the
SENSEable City Lab research group. DNC and JGB are funded in part by
Science Foundation Ireland under grant number SFI/08/CE/I1380 (Lion 2)
and by a CoEI, NUI Galway scholarship.
Author details
1
Faculty of Health, University of Plymouth, Drake Circus, Plymouth, Devon
PL4 8AA, UK. 2
International Society for Photogrammetry and Remote
Sensing, Commission IV - Geodatabases and Digital Mapping, WG IV/4 Virtual
Globes and Context-Aware Visualisation/Analysis, ISPRS Headquarters
(2008-2012), National Geomatics Centre of China, Beijing 100048, PR China.
3
SENSEable City Lab, Massachusetts Institute of Technology (MIT),
Cambridge, MA 02139, USA. 4
Institute for Geoinformatics and Remote
Sensing, University of Osnabrueck, 49076 Osnabrueck, Germany. 5
School of
Engineering and Informatics, National University of Ireland Galway, Ireland.
6
Digital Enterprise Research Institute (DERI), National University of Ireland
Galway, Ireland. 7
Department of Earth and Space Science and Engineering,
York University, Toronto, ON M3J 1P3, Canada. 8
International Society for
Photogrammetry and Remote Sensing, Commission III - Photogrammetric
Computer Vision and Image Analysis, WG III/4 - Complex scene analysis and
3D reconstruction, ISPRS Headquarters (2008-2012), National Geomatics
Centre of China, Beijing 100048, PR China. 9
Pacific Northwest National
Laboratory, Richland, WA 99352, USA. 10
InSTEDD (Innovative Support to
Emergencies, Diseases and Disasters), Palo Alto, CA 94306, USA. 11
ITRI
(Industrial Technology Research Institute), Hsinchu County 310, Taiwan.
Authors’ contributions
MNKB conceived and drafted the manuscript with equal (in terms of
importance and/or word count) contributions and expert insight from BR,
DNC, JGB, GS, RB, WAP, EJ and K-YSC. MNKB also conducted the core
literature review, identified and reflected on the main trends in the field,
located and invited the co-authors on this paper, and edited their
contributions. All authors read and approved the final manuscript.
Commercial products and company/brand names mentioned in this paper
are trademarks and/or registered trademarks of their respective owners.
Competing interests
The authors declare that they have no competing interests.
Received: 10 December 2011 Accepted: 21 December 2011
Published: 21 December 2011
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doi:10.1186/1476-072X-10-67
Cite this article as: Kamel Boulos et al.: Crowdsourcing, citizen sensing
and sensor web technologies for public and environmental health
surveillance and crisis management: trends, OGC standards and
application examples. International Journal of Health Geographics 2011
10:67.
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