This paper describes a 3-D Pseudospectral Time-Domain full-wave simulator for solving large-scale electromagnetic scattering problems and radar sounding applications. The simulated 3-D backscatter and bistatic scattering radar cross sections are compared with analytical solution of lossless and lossy dielectric spheres. The PSTD solver is applied to simulating the surface scattering of a Martian moon - Phobos using the MARSIS's radar characteristics and viewing geometry. Utilizing GPU parallelization, the simulation is performed on a kilometer-scale domain with enhanced efficiency in both time and memory as well as better accuracy, demonstrating its superiority in large-scale radar sounding simulations by using the full-wave method.

This article presents a study to assess the characteristics of particles or bubbles possibly present on Titan’s lakes and seas using Cassini RADAR observations when operating in altimetry/sounder mode. We developed an analytical model for the surface-to-volume power ratio (SVR), which includes the principles of radiative equilibrium and Mie scattering theory. The model considers the effects due to extinction phenomena and can be used to extract valuable information on the presence of dust particles or bubbles in Titan’s liquid bodies. The absence of volume scattering in the altimetric waveforms is used to constrain the maximum density at various radii of the possible presence of nitrogen bubbles or solid particles, such as water ice, nitriles, and tholins.

Nadir-Looking low frequency radar sounders cannot easily resolve off-nadir surface returns from the subsurface nadir echoes. Cross-track surface echoes (also named ‘clutter’) with time delays synchronized with subsurface returns are renowned for being a major challenge for scientists as they can affect the analysis of orbital radar sounders data. We present a method for clutter discrimination and surface/subsurface slope estimation using data acquired from radar sounders in closely spaced repeated orbits configuration. The method takes advantage of cross-track signal migration to discriminate off-nadir clutter from subsurface signal returns received at the nadir. The migration of the off-nadir signals is also used to determine the clutter Direction-of-Arrival (DOA) as well as the surface/subsurface cross-track slopes. The effectiveness of the method has been proven on the MRO’s Shallow Radar (SHARAD) dataset and provides a proof-of-concept demonstration for the surface clutter discrimination when radar sounders repeated-passes data are available.

We re-adapt an UltraWide-Band (UWB) processing to enhance range resolution of the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) up to a factor six (25m). The technique provides for the estimation of radar signature over a wider spectrum via the application of well-known super-resolution (SR) techniques to adjoining sub-bands. The measured spectra are first interpolated and then extrapolated outside the original bands. The revised algorithm includes the estimation and removal of ionospheric effects impacting the two signals. Because the processing requires the realignment of the echoes at different frequencies, we derived the maximum tolerable retracking error to obtain reliable super-resolved range profiles. This condition is fulfilled by low-roughness areas compared to MARSIS wavelength, that proves to be suitable for the application of our processing. Examples of super-resolved experimental products over different geological scenarios shows the detection of shallow dielectric interfaces not visible from original MARSIS products. Our results are validated by comparison with the Shallow Radar (SHARAD) data acquired at the crossovers, demonstrating the potential of the method to provide enhanced imaging capabilities.

In a recent study, a 2-D pseudospectral time-domain (PSTD) full-wave simulator was developed and demonstrated to be capable of efficiently solving large-scale low-frequency (e.g., HF) electromagnetic scattering problems, for example, on the application of radar sounding simulations of planetary clutter and subsurfaces. In this article, the 2-D PSTD simulator is applied to simulate a domain as large as 4000$\lambda $(along-track)$\times 1666.67\,\,\lambda $(cross-track)$\times 33.33\,\,\lambda $(depth) with$\lambda =15$m at an HF frequency of 20 MHz. To accomplish the goal, the simulator is further improved to efficiently model/simulate large cross-track slices of dielectric scenes by allowing nonuniform grid sampling in horizontal (lateral) and vertical directions, and the cross-track results are then stitched together along the track to form the simulated radargram. By combining the SHAllow RADar (SHARAD) viewing geometry and Mars Orbital Laser Altimeter (MOLA) digital elevation model (DEM), we simulate SHARAD returns at three different sites on Mars: one at the North Pole and two at Oxia Planum. At all three sites, the PSTD simulated radargrams are compared with measured SHARAD radargrams. Through power-level calibration and reference time adjustment, the PSTD simulated power estimates are further validated by comparing with real power observations from SHARAD with a 5-dB uncertainty and Pearson correlation coefficient of 0.3–0.4 (a$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.

The Cassini RADAR altimeter has provided broad-scale surface topography data for Saturn's largest moon Titan. Herein, we adapt the delay/Doppler algorithm to take into account Cassini geometries and antenna mispointing usually occurring during hyperbolic Titan flybys. The proposed algorithm allows up to tenfold improvement in the along-track resolution. Preliminary results are provided that show how the improved topography presented herein can advance our understanding of Titan's surface characteristics.

We consider an acquisition system constituted by an array of sensors scanning an image. Each sensor produces a sequence of readouts, called a time series. In this framework, we discuss the image estimation problem when the time series are affected by noise and by a time shift. In particular, we introduce an appropriate data model and consider the least squares (LS) estimate, showing that it has no closed form. However, the LS problem has a structure that can be exploited to simplify the solution. In particular, based on two known techniques, namely, separable nonlinear LS and alternating LS, we propose and analyze several practical estimation methods. As an additional contribution, we discuss the application of these methods to the data of the photodetector array camera and spectrometer, which is an infrared photometer onboard the Herschel satellite. In this context, we investigate the accuracy and the computational complexity of the methods, using both true and simulated data.