Study of the stability of the ScaRaB shortwave channel. Application: determination of uniform desert zones

The first flight model of ScaRaB (Scanner for Earth Radiation Budget) on board the Russian Meteor-3/07 weather satellite (altitude 1200 km; inclination, 82.56 ) transmitted data over a period of 1 year (24 February 1994-5 March 1995). We use solar channel (shortwave radiation, 0.2 mu m-4.0 mu m) data over desert regions (clear-sky scenes) to study the stability of the radiometer signal. We consider 1.25 1.25 areas in desert regions and we compute bi-directional reflectance for these areas. These values, depending on the three angles defined by the Sun-target-satellite geometry, are grouped by a similar angular configuration for each area. In this way it is possible to compare reflectance, with the same illumination and observation geometry, for different months, for each area. The results show great stability of the reflectance values, demonstrating the stability of the radiometer signal. For computing variability of the reflectance for each area (the relative standard deviation over an area) we study uniform desert zones. The low-variability zones agree very well with uniform zones selected by Cosnefro' for CNES (Centre National d'Etudes Spatiales, France) in the Saharan and Arabian deserts, from Meteosat-4 data. This demonstrates the high quality of the ScaRaB shortwave radiometer which scans with a pixel size 540 times greater than Meteostat-4.