Handbook of best practices

While the SOS provides an interface for actively querying observational information, there is
also a need for being able to subscribe to certain sensor events, e.g. if a certain threshold
value is exceeded by a sensor output. For this purpose, the Sensor Event Service (SES) and
the Web Notification Service (WNS) have been defined 7 . The SES allows to subscribe to
certain sensor events and the WNS can be utilized to notify subscribed users in case of
certain events. As an example, SES and WNS allow users to register to an event “sea
surface level above 5 meters” and to be notified via SMS, if this value is exceeding at a
certain sensor station. This is in particular useful for sensor maintainers, e.g. if unusual
values are reported, or in disaster management applications to detect severe weather
events. While the SOS and the Sensor Planning Service (SPS) are official implementation
standards, the SES and the WNS are published as discussion papers. As such, they are not
official standards yet. They may be replaced in future by a general publish-subscribe
interface that is currently under development by the OGC Pub/Sub Standards Working
Group.
The Sensor Planning Service (SPS) can be used to task sensors via the internet 8 . The web
service offers operations for registering new sensors, for retrieving information about
registered sensors and tasking capabilities and for executing task. As examples, the SPS
can be used to change the sampling rate of a sensor station or to re-locate sensors, if these
are mounted on mobile platforms.
6.1.4 SWE applications
Sensor Web technologies are already in use in a variety of different domains and use cases.
Examples are the usage of SOS servers by the European Environmental Agency to collect
air quality measurements from the European member states or the U.S. Integrated Ocean
Observing System (IOOS) where oceanographic measurements are served via the SOS
interface.
Several implementations of SWE standards are available. The most widely used open
source SOS implementation, the 52N SOS, is maintained by the 52°North open source
initiative 9 . Furthermore, 52°North implements the full suite of SWE services including SPS,
SES and WNS and provides several client implementations to use them, e.g. in Web
browsers. Further implementations of SOS servers are also available, e.g. the istSOS
implemented in Python 10 or a C-based extension of the UMN map server 11 . Commercial
SOS implementations are available as well, e.g. by Northrop Grumman.
6.1.5 Perspectives for ocean observatories
A common way and best practice to apply Sensor Web technologies in the oceans domain
are not yet available and are currently being investigated, e.g. by the FP7 NeXOS project 12 .
Therein, a Sensor Web architecture has been defined and is currently being developed as
prototypical implementation. Further European research projects will also explore the usage
of SWE in the Ocean domain, e.g. ODIP, ODIP 2, COMMON SENSE, or BRDIGES.
7 The WNS and SES discussion papers are accessible at http://www.opengeospatial.org/standards/dp
8 http://www.opengeospatial.org/standards/sps
9 http://www.52north.org
10 https://geoservice.ist.supsi.ch/projects/istsos/index.php/Welcome_to_istSOS_project
11 http://mapserver.org/de/ogc/sos_server.html
12 http://www.nexosproject.eu/
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