Custom SHARAD Processing via the CO-SHARPS Processing Boutique

Introduction: Prior to the orbit insertion of the Mars Reconnaissance Orbiter in 2006, the Shallow Radar (SHARAD) Team developed software to apply a standard set of radar processing parameters to the data, which was implemented at the SHARAD Operations Center (SHOC) in Rome and included delivery of products to NASA’s Planetary Data System (PDS) [1]. At the same time, U.S. members of the SHARAD Team identified the need for custom processing capabilities, and they developed alternative software for that purpose. Early in the mission, the team built a web-based interface to the U.S. processing code and products that allows users to choose and apply a range of parameters for two different radar processors and a clutter simulator. The U.S. processors and web interface are currently installed at the Southwest Research Institute’s Boulder office and are collectively referred to as the Colorado Shallow Radar Processing System, or CO-SHARPS. In 2014, access to the CO-SHARPS Processing Boutique was opened up to individuals outside of the SHARAD Team. SHARAD Processors: The Italian SHOC processor uses a fixed set of parameters to produce standard SHARAD radargrams, including the summing of raw radar pulses to produce an along-track frame interval of 300 m and Hann weighting to suppress sidelobes [1]. Focusing and mitigation of ionospheric distortion effects is achieved using a phase-gradient autofocus algorithm [2]. The focused processor developed by the Smithsonian Institution (SI) [3] sums raw radar pulses to a fixed output frame interval matched to the grid spacing of the Mars Orbiter Laser Altimeter (MOLA) global elevation map (128 ppd, ~460 m [4]). Users may choose from four weighting methods to trade between sidelobe suppression and vertical resolution, set focusing apertures between 256 and 3072 frames, and adjust the multilook bandwidth. Optionally, users may also choose to create ground-track maps and unfocused radargrams. The SI processor uses an image-optimization autofocusing technique [3]. In 2014, SI began delivery of a standard set of products to the PDS that supplements the Italian deliveries [5]. The focused processor developed by the Jet Propulsion Laboratory (JPL) allows users to specify the summing of raw frames, which establishes the output frame interval [6]. Range-compression weighting may be set to either Hann or uniform, and the aperture is fixed at 4096 raw frames. The JPL processor employs the Chapman model for correction of ionospheric phase distortion and an omega-K focusing algorithm [7], and it also provides for the generation of depthconverted radargrams by specifying a dielectric permittivity to use below the MOLA-predicted surface return. To aid the interpretation of radargrams, the University of Texas (UT) developed a incoherent facet-based clutter simulator that enables one to distinguish offnadir surface returns from likely subsurface returns in radargrams [8]. The simulator determines surface facets from a digital elevation model (DEM) along the ground track for single SHARAD observations. The UT simulator at CO-SHARPS uses MOLA DEMs, and users may run it in tandem with the JPL processor. Web Interface: Access to CO-SHARPS requires user authentication via secure shell. New users may request an account from the web page at http://boulder.swri.edu/sharad.php. Upon receiving access credentials and logging into the CO-SHARPS web interface, users will be presented with a menu that includes links to the CO-SHARPS Processing Boutique and the SHARAD PDS site for reference. Within the Processing Boutique, users may specify the processor and pa-