MetOp-SG MWI Testing: Development and Validation of Complex TVAC Test Setup for the Instrument Performances Characterization Including Radiometric Targets

The MicroWave Imager Instrument (MWI) is part of the payload complement of the MetOp-SG Satellites type B. MWI is a conical scanning radiometer, with multiple frequency channels. The main goal of the MWI is to serve operational meteorology and oceanography by providing precipitation monitoring as well as sea ice extent information, in support of long-term climate records. The On Ground Calibration Targets (OGCT) are temperature controlled microwave blackbodies, that allow MWI instrument RF stimulation with a known reference for the on-ground radiometric performance and calibration tests, both in thermal-vacuum conditions and in ambient conditions. The instrument is calibrated on ground with temperature accuracy better than 0.3 K, before flight. For the thermal-vacuum tests two OGCTs are required: a Thermal-Vacuum Earth Target (TVET) that is a variable temperature target simulating the variable brightness temperature of the measured scene to be placed in front of the instrument main reflector and a Thermal-Vacuum Cold Sky Target (TVCT) that is a fixed temperature target to be placed in front of the Cold Sky reflector simulating the cold sky temperature. The Radiometric Performance Test (RPT) has the goals of verifying that the instrument is compliant with the radiometric performance requirements and of determining the calibration curve coefficients in the nominal thermal-vacuum conditions. Thermal Vacuum Thermal Cycling Test (TVTC) and RPT are the two main parts of the MWI TVAC test campaign. The present paper describes the complex TVAC test setup with all the challenges encountered. Design features and challenges of the TVAC targets design are presented too. Finally, the multi-physic workflow that leads to the BT calculation and the development of a look-up table in order to compute the targets BT on-the-fly during the test using thermal sensors values as inputs is addressed.