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Algorithm for MERIS land surface BRDF/albedo retrieval and its validation using contemporaneous EO data products

Jan-Peter Muller(1) , Carsten Brockmann(2) , Norman Fomferra(2) , Jürgen Fischer(3) , Réné Preusker(3) , and Peter Regner(4)

(1) University College London, Gower Street, London WC1E 6BT, United Kingdom
(2) Brockmann Consult, Max-Planck-Str. 2, 21502 Geesthacht, Germany
(3) Freie Universität Berlin, Carl-Heinrich-Becker-Weg 6-10, 12165 Berlin, Germany
(4) ESA, Via G. Galilei, 00044 Frascati, Italy

Abstract

An algorithm is described for the generation of a global BRDF/albedo at 16-days (0.05º) and monthly (10km and 0.1º) land surface product for 2003 which uses as inputs Spectral surface Directional Reflectances, SDRs (Schröder et al., Preusker et al., this workshop) for 13 of the 15 MERIS L1,2 bands. Owing to the lack of sufficient directional samples for most of the Earth’s land surface, even for a monthly time period, direct inversion of BRDF parameters are not possible. Instead the 16-day MODIS BRDFs at 0.05º resolution (derived using either full inversions or magnitude inversions from the 2001 MODIS values) are employed in a magnitude inversion scheme for the 4 common MERIS (490±5 [b3], 560±5 [b5], 665±5 [b7], 865±10 [b13]) bands with MODIS (459-479 {b3}, 545-565 {b4}, 620-670 {b1}, 841-8766 {b2}). Spectral interpolation to the remaining 9 MERIS bands and to 4 broadband (0.4-0.7µm, 0.7-0.9µm, 0.7-3µm, 0.4-3µm) is then performed. Finally, temporal interpolation using weights based on the number of MERIS SDRs within a corresponding 16-day MODIS time window and the position of the 16-day window within a month is used to create a monthly product. These products will be generated for use by the MERIS ground segment to improve the retrieval of atmospheric and cloud parameters as well as have potential use by climate GCM modellers.

A few products have been generated and these have been compared against contemporaneous MODIS spectral albedos (over 16-days) and MISR and POLDER products (over a month) and the results shown. A quality assessment of the BRDF correction will also be shown using overlapping NBAR (Nadir BRDF Adjusted Reflectances) applied to individual orbits. This work was supported under ESA/ESRIN contract 18348/04/I-LG.

 

Workshop presentation