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Application of the SCAPE-M atmospheric correction algorithm to the processing of MERIS data over continental water bodies

Luis Guanter(1), Jose Antonio Dominguez-Gomez(2), Laura Conde-Bueno(2), Antonio Ruiz-Verdu(2), Victor Estelles(3), Ramon Pena(2) and Jose Moreno(3)

(1) GeoForschungsZentrum-Potsdam, Telegrafenberg, A17, 14473, Potsdam, Germany
(2) Centre for Hydrographic Studies of CEDEX, Paseo Bajo de la Virgen del Puerto, 3, 28005, Madrid, Spain
(3) University of Valencia, Dr. Moliner, 50, 46100, Burjassot-Valencia, Spain

Abstract

The Self-Contained Atmospheric Parameters Estimation from MERIS data (SCAPE-M) atmospheric correction algorithm was presented in the last ENVISAT Symposium 2007. It derives aerosol optical thickness (AOT), columnar water vapour and surface reflectance from MERIS Level 1b data over land. The algorithm is implemented as a compact package which processes MERIS images in an automatic manner. The product reader and the modules for digital elevation model (DEM) extraction and geometric correction implemented in the ENVISAT MERIS and AATSR Toolbox (BEAM) software are used in the processing by means of external calls of SCAPE-M to BEAM libraries. A DEM is used in topographic and elevation correction along the atmospheric correction process. Atmospheric adjacency effects are also compensated by means of a simple approach considering the target surroundings and the atmospheric turbidity. An atmospheric look-up table based on the MODTRAN4 radiative transfer code enables to speed-up the calculations.

Even though SCAPE-M was initially intended for the processing of images acquired over land surfaces, it was extended to enable the processing of continental waters. While oceans and the largest inland water bodies are masked out from the processing, water bodies with an area up to 400 km2 and the ocean areas closer than 10 km to the coast are processed. Those water pixels are considered by the AOT retrieval algorithm as dark targets in order to complement the aerosol retrieval. Continuous AOT and reflectance maps are then derived from MERIS images over continental targets.

A short review of SCAPE-M and the main results obtained from the processing of MERIS images acquired over continental water bodies are presented in this contribution. MERIS-derived water-leaving reflectance spectra are validated by means of the comparison with ground-based measurements. A dedicated field campaign was conducted during 2007 in six reservoirs in Spain, in the framework of the ESA’s MERIS Lake Water Algorithms Development project. A total of six MERIS images with simultaneous ground-based reflectance and AOT measurements were available from this campaign, which led to up to 10 points for reflectance and AOT validation. In addition, MERIS data from other 3 validation campaigns between 2003 and 2005 have been used. The good agreement between MERIS-derived and in-situ measurements of AOT and water reflectance showed the applicability of SCAPE-M for the processing of medium-size continental water bodies.

 

Workshop presentation

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