Validation of a Pseudospectral Time-Domain (PSTD) Planetary Radar Sounding Simulator With SHARAD Radar Sounding Data

Abstract

In a recent study, a two-dimensional (2-D) Pseudospectral Time-Domain (PSTD) full-wave simulator was developed and demonstrated to be capable of efficiently solving largescale low-frequency (e.g. HF) electromagnetic scattering problems e.g. on the application of radar sounding simulations of planetary clutter and subsurfaces. In this paper, the 2-D PSTD simulator is applied to simulate a domain as large as 4000 λ (along-track) × 1666.67 λ (cross-track) × 33.33 λ (depth) with λ = 15 m at HF frequency of 20 MHz. To accomplish the goal, the simulator is further improved to efficiently model/simulate large cross-track slices of dielectric scenes by allowing nonuniform grid sampling in horizontal (lateral) and vertical directions, and the crosstrack results are then stitched together along the track to form the simulated radargram. By combining the SHAllow RADar (SHARAD) viewing geometry and Mars Orbital Laser Altimeter (MOLA) Digital Elevation Model (DEM), we simulate SHARAD returns at three different sites on Mars: one at the North Pole and two at Oxia Planum. At all three sites, the PSTD simulated radargrams are compared with measured SHARAD radargrams. Through power level calibration and reference time adjustment, the PSTD simulated power estimates are further validated by comparing with real power observations from SHARAD with a 5 dB uncertainty and Pearson correlation coefficient of 0.3-0.4 (p-value on the order of 10 −9 ), which justifies the use of the 2-D PSTD simulator for emulating surface clutter in planetary radar sounding. This simulator is open source and can be easily modified to support radar sounding simulations in support of other planetary missions with radar sounding instruments.

An Improved Method of Surface Clutter Simulation Based on Orbiting Radar in Tianwen‐1 Mars Exploration

“…The simulators proposed by our paper can not only simulate the surface echo of MOSIR but also can be used for future Jupiter satellite sounding radars, for example, REASON on NASA Europa clipper mission (Blankenship et al., 2018) and RIME on ESA JUICE mission (Bruzzone & Croci, 2019). However, there are many numerical solutions to Maxwell's equations well developed and applied in the radar echo simulation, such as the finite difference time domain (FDTD; Eide et al., 2021; Yee, 1966), the finite element time domain method (Pursiainen & Kaasalainen, 2016; Sorsa et al., 2019), and the pseudospectral time‐domain (Lei et al., 2022; Q. H. Liu, 1997). These algorithms can obtain very accurate electromagnetic simulation results but require a large number of computing recourses.…”

Clutter Detection and Surface/Subsurface Slope Determination by Combination of Repeat-Pass Sounder Orbits Applied to SHARAD Data

“…Digital Object Identifier 10.1109/LGRS.2022.3223882 discrimination is performed by visual [4], [5] or automatic [6] comparison between sounder data products ("radargram", RDR) and simulated products ("cluttergram") obtained using digital elevation models (DEMs) of the surface. However, this approach enables clutter identification only when the off-nadir clutter is exposed, and surface topography is available at a better scale than the radar ground resolution.…”