Impact of Out-of-the-Swath Knowledge on the Antenna Pattern Correction Performance Applied to Conical Scanning Spaceborne Radiometers

The future Copernicus Imaging Microwave Radiometer (CIMR), funded by the European Commission and developed by the European Space Agency (ESA), will include a spaceborne radiometer able to provide the highest ground spatial resolution as of launch date for C- to Ka-bands, due to its large deployable mesh reflector able to produce images over a swath 2000 km wide. Because of side and grating lobes in the patterns, the antenna subsystem introduces distortions in the acquired data that result in a loss of radiometric accuracy caused by unwanted energy collected far from the antenna boresight. A candidate antenna pattern correction (APC) algorithm based on an iterative formulation that takes advantages of measurements belonging to the same swath was already proposed by the authors. As the antenna boresight moves closer to the edges of the swath, the antenna pattern (AP) senses regions not already observed, where the correction needs a guess or auxiliary out-of-swath information. This article evaluates the performance of the candidate APC algorithm according to various possible a priori assumptions. Eventually, an evaluation is performed using a timeseries derived from Special Sensor Microwave/Imager enhanced-resolution data. This was done to get a first assessment of the impact of past ancillary information on the APC process.