Reference Radiometer of SMOS: Development and Calibration

Three Flight Models (FM) of the reference ra- diometer of European Space Agency's SMOS mission have been developed and tested. SMOS stands for Soil Moisture and Ocean Salinity. The reference radiometeris a Noise Injection Radiometerand hence named as NIR; the NIR FM's have been developed by Elektrobit Microwave Ltd. in collaboration with Laboratory of Space Technologyof Helsinki University of Technology, which has acted as a subcontractor. The NIRs will be integrated into the MIRAS ( Microwave Imaging RadiometerUsing Aperture Synthesis) payload in 2006. The MIRAS is the sole instrument onboard SMOS satellite. MIRAS has 66 regular receiver units (called LICEF) and three NIR units. The purpose of NIR subsystem is (1) to provide precise measurement of the average brightness temperaturescene for absolute calibration of the MIRAS image map, (2) to measure the noise temperaturelevel of internal active calibration sources for individual receiver calibration (named Calibration Subsystem, CAS), and (3) to form interferometer baselines, so-called mixed baselines, with the regular receiver units. The performance of the NIR is a decisive factor of the overall MIRAS performance. In this paper we present the design of the NIR flight models, the test campaign results, and both ground and orbital calibration techniques including the ground calibration results.