Bistatic Radar Observations in 2022 with Mars Express

The Mars Express Radio Science Experiment (MaRS) [1] performs bistatic radar measurements (BSR) every two years during the opposition between Earth and Mars when the distance between them is smallest. In 2022, three measurements were successfully executed at the end of November and December over different regions of Mars.

The dielectric properties and surface roughness of Mars can be determined using BSR measurements [2, 3]. In this process, the radio subsystem transmitter sends right circularly polarized (RCP) radio signals at two wavelengths, X-Band and S-Band, toward Mars' surface. Part of the transmitted radiation is then scattered back toward a receiver at a ground station on Earth. Both the right and left circularly polarized echo components (RCP and LCP, respectively) are recorded at the ground station.

The dielectric constant can be derived from the RCP-to-LCP power ratio, eliminating the need for absolute end-to-end calibration. Instead, relative calibration of the RCP and LCP ground receiver channels can be used. However, achieving accurate relative calibration of the two receiving channels remains challenging.

To improve the calibration procedure, an additional step has been added. This step involves pointing the 70 m ground station toward a radio source during the post-calibration process. A comparison between the old and new calibration procedures will be presented, along with initial results for the dielectric constant from all three measurements conducted in 2022.

References

[1] M. Pätzold et al., “Mars Express 10 years at Mars: Observations by the Mars Express Radio Science Experiment (MaRS),” Planetary and Space Science, vol. 127, pp. 44–90, Aug. 2016.

[2] R. A. Simpson, G. L. Tyler, M. Pätzold, and B. Häusler, “Determination of local surface properties using Mars Express bistatic radar,” Journal of Geophysical Research (Planets), vol. 111, no. #E10#, p. 6, 2006.

[3] R. A. Simpson, G. L. Tyler, M. Pätzold, B. Häusler, S. W. Asmar, and A. K. Sultan-Salem, “Polarization in Bistatic Radar Probing of Planetary Surfaces: Application to Mars Express Data,” Proceedings of the IEEE, vol. 99, no. 5, pp. 858–874, 2011.

Acknowledgements

The Mars Express Radio Science Experiment (MaRS) is funded by the Deutsches Zentrum für Luft- und Raumfahrt, Bonn-Oberkassel, under grants 50QM1004 and 50QM1005. We thank the ESA Mars Express Science Operations teams, the MEX Flight Control Team, and the NASA Deep Space Network for their support. Special thanks to the NAIF group at JPL, headed by Charles Acton, for their assistance with the SPICE software package.