A COMPARISON OF TOTAL SHORTWAVE SURFACE ALBEDO RETRIEVALS FROM MODIS AND TM DATA

Total shortwave albedo is one key variable controlling the radiation energy budget of the land surface. Thus, the monitoring of its spatial and temporal variations is one important issue e.g. for the application of climate models. Routine albedo products are available from the Moderate Resolution Imaging Spectroradiometer (MODIS), e.g. MODIS MCD43A3 as 16-day 500m combined product generated from data of Terra and Aqua MODIS. Furthermore, surface spectral reflectances from monotemporal multispectral sensor data may be used to estimate broadband albedos; for this purpose, conversion formulae have been developed for a number of sensors. Mismatches between different albedo products may arise e. g. from the atmospheric correction process, different scan view geometries, BRDF adjustments, the range of wavelengths used or the particular narrowband to broadband conversion formulae. In this study, albedo retrievals from Thematic Mapper (TM) data and MODIS data/products were analysed for their consistency. In detail, the following MODIS products were considered: MOD09 - daily bidirectional surface reflectance, and 16 days albedo-product MCD43A3. To allow a comprehensible comparison between TM and MODIS, TM data have been aggregated to 500m MODIS resolution using the Point Spread Function (PSF) of MODIS. The analysis was performed for different acquisition periods, which resulted in different levels of consistency and thus uncertainties associated with the particular products.