A novel pointing technique for the enhancement of Tropospheric Delay Calibration System performances

Abstract

The beam-crossing is a novel technique aimed at reducing residual tropospheric Doppler noise for microwave radiometer calibrations. In this work, we report the findings of the first test of this technique using ESA's Tropospheric Delay Calibration System (TDCS) at the complex in Malargue. The data consists in 14 tracking passes of the BepiColombo spacecraft collected between October 2023 and March 2024 during two separate test campaigns. We analyzed the performance of the beam-crossing technique and compared it with the nominal radiometer pointing through the analysis of the Doppler residuals extracted from the orbit determination process. Results show that the beam-crossing performed similarly to the standard pointing, with modest noise reductions and improved stability only at time scales between 100 s and 300 s. Key factors affecting the results include the antenna elevation and the boundary layer height, indicating the need to revisit initial test assumptions, which comprised a fixed boundary layer. Furthermore, comparing the beam-crossing test results with those obtained during the first two BepiColombo superior solar conjunction experiments highlights a potential application of this technique during periods of solar conjunction. However, technical challenges, adverse weather, and limited Ka-band transponder use, reduced the number of analyzed tracking passes. Future studies should therefore expand the dataset to consolidate the results. Furthermore new theoretical studies and test campaigns should elaborate on the selection process for the optimal crossing height.