SPONGE: Spaceborne Observations to Nourish GEMS/Water

SPONGE aims to demonstrate how satellite remote sensing and in particular Europe's new Sentinel satellites can facilitate water resource management information for the UNEP GEMS/Water programme and the broader UN water community. SPONGE is a 2-year ESA Data User Element Innovators III project and was started in 2015.

GEMS/Water is a UNEP initiative that supports global, regional and national environmental assessments and reporting processes on the state and trends of water resources. Its GEMS/Water Data Centre at the German Federal Institute for Hydrology collects surface water quality measurements from National Focal Points in participating countries, and makes them accessible through the GEMStat database. Satellite Earth observation was identified as a promising tool to improve the spatio-temporal representativeness of GEMStat.

 
In spite of its unparalleled size, the global representativeness of freshwater monitoring data in GEMStat is limited to participating countries, and the in situ sampling station density within those countries is very unbalanced. Further limitations are due to sampling frequencies and the parameters available in each site.

In spite of its unparalleled size, the global representativeness of freshwater monitoring data in GEMStat is limited to participating countries, and the in situ sampling station density within those countries is very unbalanced. Further limitations are due to sampling frequencies and the parameters available in each site.

 

The SPONGE project provides for a 1-year satellite Earth observation pilot service for GEMStat. Water quality parameters, reference locations and product specifications are defined in collaboration with several National Focal Points and the German Federal Institute for Hydrology. Satellite image acquisitions plans are provided to National Focal Points in order to improve the availability of reference data for Earth observation product development. Validated and reviewed Earth observation products are finally included in GEMStat.

 
GEMS/Water is directly involved in all main project tasks of SPONGE, and accounts for planning and data exchange activities related to the National Focal Points. Odermatt & Brockman and Brockmann Consult provide for the technical tasks.

GEMS/Water is directly involved in all main project tasks of SPONGE, and accounts for planning and data exchange activities related to the National Focal Points. Odermatt & Brockman and Brockmann Consult provide for the technical tasks.

 

The Copernicus programme by ESA and the European Commission is an unprecedented effort to advance the operational potential of Earth observation, and to ensure the continuity of Earth observation data supply throughout the next decades. Its satellite fleet, the so-called Sentinels, are designed to meet a wide range of application-specific requirements. The first two Sentinel-2 satellites, launched in June 2015 and presumably 2016, will enable inland water quality monitoring at a spatial resolution of 10-20 m and a temporal resolution of 5 days or less, and are the primary data source for the SPONGE pilot service. Possible contributions to GEMStat by Sentinel-1 and Sentinel-3 are also assessed.

 
Artistic depiction of a Sentinel-2 satellite in orbit. The Multi-Spectral Instrument (MSI) on-board Sentinel-2s falls into line with Landsat and SPOT instruments, but provides a significantly higher temporal resolution as required for freshwater monitoring (image by ESA/ATG medialab).

Artistic depiction of a Sentinel-2 satellite in orbit. The Multi-Spectral Instrument (MSI) on-board Sentinel-2s falls into line with Landsat and SPOT instruments, but provides a significantly higher temporal resolution as required for freshwater monitoring (image by ESA/ATG medialab).

 

The potential of Earth observation to improve water quality monitoring in Lake Geneva was evaluated in collaboration with the Swiss Federal Institute of Technology in Lausanne. A 2002-2012 chlorophyll-a dataset from ENVISAT-MERIS was provided by Odermatt & Brockmann and the Diversity II project team, and compared to the bi-weekly in situ measurements performed by the Alpine Centre for Research on Trophic Networks and Lake Ecosystems in Thonon. The in situ measurements allowed verifying overall trends and calibrate coincident observations, but were found too scarce to resolve phytoplankton dynamics during spring blooms or in estuary regions. SPONGE relies particularly on the study's recommendations how to combine in situ monitoring programmes with remote sensing.

 
The in situ reference site SHL2 represents the spring phytoplankton variability in Lake Geneva for a large area of intermediate chlorophyll-a concentrations. Site GE3 represents the less productive Petit Lac in the west (site locations indicated by black crosses on the right). The most productive area near the Rhone estuary in the east remains however unrepresented (from Kiefer et al., 2015).

The in situ reference site SHL2 represents the spring phytoplankton variability in Lake Geneva for a large area of intermediate chlorophyll-a concentrations. Site GE3 represents the less productive Petit Lac in the west (site locations indicated by black crosses on the right). The most productive area near the Rhone estuary in the east remains however unrepresented (from Kiefer et al., 2015).

 
Kiefer, I., Odermatt, D., Anneville, O., Wüest, A., and Bouffard, D. (2015). Application of remote sensing for the optimization of in-situ sampling for monitoring of phytoplankton abundance in a large lake. Sci. Total Environ. 527–528, 493–506.