International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B4, 2012 
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia 
SENSOR WEB SERVICES FOR EARLY FLOOD WARNINGS 
BASED ON SOIL MOISTURE PROFILES 
Thomas Brinkhoff^ *, Stephan Jansen b 
? Jade University Oldenburg, Institute for Applied Photogrammetry and Geoinformatics, 26121 Oldenburg, Germany - 
thomas.brinkhoff@jade-hs.de 
b OFFIS Institute for Information Technology, 26121 Oldenburg, Germany - stephan jansen@offis.de 
Commission IV, WG IV/2 
KEY WORDS: Sensor, Monitoring, Floods, Environment, Internet/Web, Services, Interoperability, Visualization 
ABSTRACT: 
As result of improved computing and communication capabilities, the use of sensors and sensor networks for environmental 
monitoring has gained considerable importance in the recent years. For an interoperable integration of sensor data like sensor 
descriptions, sensor measurements and alarm events, the Open Geospatial Consortium (OGC) started the Sensor Web Enablement 
(SWE) initiative and proposed several specifications in respect to a geospatial sensor web. First implementations of SWE software 
frameworks are available. In this paper, we present the results of the recent WEBBOS project. Its objective was to build up a system 
for early flood warnings by measuring soil moisture profiles. The use of soil moisture profiles is motivated by the fact that 
traditional approaches like the observation of water gauges are suitable for the prediction of large-river flooding but not for smaller 
drainage areas. We describe the architecture of our system and how it is built up by using existing software components to a large 
extent. Our special focus is on the incorporation of 3D soil moisture profiles into the SWE data model, on the integration of the new 
OGC Sensor Event Service, and on the development of a flexible web client for mapping and other visualization purposes. 
1. INTRODUCTION 
Recent disastrous floodings have demonstrated the demand for 
early flood warnings. This need will be enforced by the 
expected climate change that probably leads to more torrential 
rain. In general, flood forecasts concentrate on large rivers 
considering water gauges. However, there exist a large number 
of smaller drainage areas ‘with a size of 100 to 1000 square 
kilometers. In such areas, disastrous drainages may happen after 
heavy rain that cannot reasonably be observed by gauges 
because the water level changes very fast what prevents 
warnings to be made in time. 
Thus, the creation of early flood warnings for small drainage 
areas is still an unsolved challenge. One promising approach for 
solving this problem is the observation of the soil humidity 
because that measure decides how much of the precipitation 
will drain off. WEBBOS is a joint project of the Mannheim 
University of Applied Sciences and the Oldenburg University 
of Applied Sciences funded by the German Federal Ministry of 
Education and Research. It has the objective to build a web- 
based sensor system for early flood warnings by measuring soil 
moisture profiles. Within this project, special sensors measuring 
the soil humidity in different depths have been developed and 
successfully tested. These sensors were integrated into sensor 
nodes that form local sensor networks. Such a sensor network 
should be located in an area with a high variety of soil 
humidity. 
Like in other early-warning and disaster management systems, 
it is important to incorporate the sensor measurements into a 
geospatial information service that allows managing sensor 
data. This encloses the visualization of the sensor measurements 
  
* Corresponding author. 
and the control of the soil humidity sensors as well as the 
detection and processing of alarm events. Interoperability is an 
important issue for such systems. Therefore, the Open 
Geospatial Consortium (OGC) started the Sensor Web 
Enablement (SWE) initiative some years ago and specified 
several services and data models in the meantime (Botts et al, 
2006). 
WEBBOS implemented its information system using those 
specifications and a popular open-source SWE framework. 
Many standard requirements can be solved by such an approach 
without additional efforts. However, often there are important 
demands that need more sophisticated solutions. Those cases 
and their solutions for the WEBBOS project will be discussed 
in this paper. One important aspect is that the use of soil 
moisture profiles requires temporal 3D measurements and 3D 
models of soil humidity for each sensor network: Only the 
relation and difference between the humidity in different depths 
and their development over the time allow detecting relevant 
events. The temporal aspect is sufficiently covered by the 
current SWE specifications. However, these specifications and 
their implementation are mainly 2D-oriented. 
Another important issue for early-warning and disaster 
management systems is the detection of potentially dangerous 
situations. This requires the description and detection of spatio- 
temporal events. For this purpose, the OCG recently proposed 
the Sensor Event Service (SES) (Echterhoff & Everding, 2008) 
together with the Event Pattern Markup Language (EML) 
(Everding &  Echterhoff, 2008). Until now, only few 
applications of the SES exist. Thus, the experience is limited. 
430 
Interr 
Standard v 
adequate vi 
services res 
sensor mea: 
toolkits are 
can be e 
applications 
using a Jav. 
by the proj 
well as cont 
The rest of t 
we present t 
This is follc 
sensors. Sei 
generation. ' 
section We 
short summe 
2.1 Sensor: 
The observa 
requires (i) tl 
and (ii) the o 
variety of so 
are based on 
content of w 
conductivity) 
water conten 
like soil den: 
on. Thus, a r 
WEBBOS p 
developed an 
the left side 
shown on rig 
permittivity. 
  
Fig 
The demand 
humidity sen: 
observation ar 
30 to 100 m | 
base unit tha 
Project, differ. 
Node operating 
With a high v;