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MERIS Validation with respect to operational monitoring needs in the North and Baltic Sea

Kerstin Stelzer(1), Jasmin Geißler(1), Carsten Brockmann(1), Holger Klein(2), Jeanette Göbel(3), Anu Reinard(4) and Kai Sorensen(5)

(1) Brockmann Consult, Max-Planck-Str. 2, 21502 Geesthacht, Germany
(2) Bundesamt für Seeschifffahrt und Hydrographie, Bernhard-Nocht Str. 78, 20359 Hamburg, Germany
(3) Landesamt für Natur und Umwelt Schleswig-Holstein, Hamburger Chaussee 25, 24220 Flintbek, Germany
(4) Tartu University, Tõravere, Tartu County, Estonia 61 7601, Estonia
(5) NIVA, Gaustadalléen 21, NO-0349 OSLO, Norway

Abstract

MERIS provides water constituents for Case 1 (algal_1, algal_2) and Case 2 waters (algal_2, suspended matter, yellow substance) in its Level 2 product. Although Envisat has been designed as an experimental satellite, its data are acknowledged as very valuable for operational purpose, and the water constituents are used as complementary information for routine monitoring of European waters, e.g. for the European Water Framework Directive and the OSPAR and the HELCOM regional conventions. The ESA GSE project MarCoast has laid down a solid baseline for an operational service in this respect, with data mainly originated from MERIS.

The validation of MERIS products undertaken in the framework of the MERIS and AATSR Validation Team (MAVT) has the objective to prove that the water leaving reflectance and the water constituents derived from MERIS are within a certain error level compared to in-situ measurements which correspond directly to the values retrieved from the satellite measurements. The requirements of operational monitoring entities for validation of satellite measurements differ significantly from this MAVT objective. Their interest is to use the data for monitoring purpose, and it has to be proven that MERIS data are fit for this purpose. The operational users expect the satellite data to correspond to their in-situ data, whereby these are not taken for the purpose of validating satellite measurements. Direct regressions are therefore difficult to draw and can be misleading.

In the framework of MarCoast and the ESA Case2 Regional project a comparison of MERIS chlorophyll, suspended matter and yellow substance values as well as SST derived from AATSR with in-situ measurements taken by four different monitoring agencies in Germany, Estonia and Norway has been performed. Different techniques (transects, compositing, time series, scatter plots) have been employed in order to assess the agreement between the different datasets. Alternative processing methods (FUB WEW and Case2Regional processor) have been included in the analysis. A selection of the results of this work is presented here. The results of the analysis do not permit simple conclusions, but point to strong points of the different algorithms (chlorophyll retrieval), and identify also problematic areas, such as the Case2 atmospheric correction, the yellow substance retrieval and in general the retrieval of water constituents close to the shore line, which is most important for the Water Framework Directive.

 

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry