Altimetry from Planetary Radar Sounders

Abstract

Having information on the global shape of a planet as well as having precise topography information is a prerequisite for many advanced scientific studies as well as for future robotic exploration. To date there are numerous methods to obtain topographic information including laser altimetry and stereo imaging. A currently less explored method is altimetry from planetary radar sounders. However, we demonstrate the potential to create a global Martian DTM based on altimetry data derived from SHAllow RADar (SHARAD) measurements which provides results with less than 100 m rms difference when compared to the existing MOLA DTM. We have developed and implemented an algorithm to work with EDR data products as available on PDS and derive altimetry products. First, the SHARAD data are pulse compressed and dispersive ionospheric effects are corrected for. We then apply pulse re-tracking techniques adapted from terrestrial ocean altimetry to identify the surface return. From the surface return we compute the time-of-flight and hence the range from the spacecraft to the surface of the planet. These results can be used to improve our topographic knowledge of Mars, analyze temporal variations, and will be of high significance in future planetary missions such as the Europa Clipper mission. Further improvements in the range accuracy can be made by combining the radar sounding data with stereo-images, allowing to increase the geodetic accuracy of the radar for tidal measurements and improved orbit determination.