Impact of Direct Solar Radiations Seen by the Back-Lobes Antenna Patterns of SMOS on the Retrieved Images

Abstract

The European Space Agency's Soil Moisture and Ocean Salinity (SMOS) mission is devoted to the monitoring of soil moisture and ocean salinity at a global scale from L -band space-borne radiometric observations obtained with a two-dimensional interferometer. SMOS was launched in November 2, 2009, and is still collecting the interferometric data used to retrieve the brightness temperature of the Earth surface. Several external sources of brightness within the field of view of SMOS contaminate these measurements and their contributions should be removed prior to image reconstruction. One of these sources is the direct solar radiations when the sun is either below the antenna plane array (i.e., in front of the satellite) and seen by the front-lobes antenna patterns or above it (i.e., in the back of the satellite) and seen by the back-lobes antenna patterns. In the case of SMOS, the direct solar radiations are accounted for only when the sun is in front of the satellite. In the second case, their impact is considered negligible. In this paper, we will show evidence of non-negligible direct solar radiations in the retrieved temperatures when the sun is in the back of SMOS. We will also show that the sun correction algorithm implemented in the SMOS level 1 operational processor can be extended efficiently to remove such radiations.