Radar signal simulation: Surface modeling with the Facet Method

Abstract

[1] A major finding in exploration of Mars is the indication that a large quantity of water has been present on Mars. To discover the distribution of this quantity of water, the Mars Express spacecraft is carrying a spaceborne radar sounder, called Mars Advance Radar for Subsurface and Ionospheric Sounding (MARSIS), in order to map Mars subsurface dielectric characteristics. The returned radar echoes from Mars will contain both surface and subsurface reflection components, but the part of the signal we are interested in is the reflected signal from subsurface layers. To retrieve these weak deep echoes from the radar signal, a signal processing algorithm needs to be developed. In this paper, we present a computationally efficient radar signal simulation based on the use of the Facet Method as a surface modeling scheme. This simulator will be used to validate the MARSIS ground processing software and to support the interpretation of MARSIS data. The first step in the simulation algorithm definition is to model the Mars surface. Many surface modeling methods have been developed and can be found in the literature, but considering the fact that Mars surface is very smooth, the modeling algorithm we have developed uses the Facet Method. In this paper, we show that the Facet Method is an efficient scheme for modeling a relatively smooth surface, such as the Mars' surface. The instrument simulation we define makes strict reference to the MARSIS radar parameters; however, it may be used to model any radar sounder.

Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) after nine years of operation: A summary

“…For this reason, the detection of subsurface interfaces is usually validated through numerical electromagnetic models of surface scattering, such as those by Nouvel et al (2004). Such models are used to produce simulations of surface echoes, which are then compared to real echoes detected by the radar (see Fig.…”

“…To circumvent this problem, a calibration method has been developed in Mouginot et al (2009), using surface scattering simulations such as those described in Nouvel et al (2004). The method is based on the observation that power reflected by a natural surface depends both on its composition and on its geometry (see Picardi et al, 2004a, for a discussion).…”

The 3–5MHz global reflectivity map of Mars by MARSIS/Mars Express: Implications for the current inventory of subsurface H2O

“…A method for simulating MARSIS echo histories due to local topography has been developed to help in the interpretation of the observational data. For this simulation, the surface is modeled using the facet method (Nouvel 2002;Nouvel et al 2004), which is an extension of the Kirchhoff model. Such a model can be used because of the low surface roughness at radar wavelengths and offers a significant gain in calculation time.…”

Accumulation and Erosion of Mars' South Polar Layered Deposits

“…There are several bands (packets) containing many thin reflectors running parallel or subparallel to the surface, separated by thicker dark bands. To determine if they arise from subsurface interfaces or come from surface topographic features at the same time delay, we ran a highfidelity model of the expected conttibution of offnadir topographic clutter using Mars Orbiter Laser Altimeter (MOLA) data ( 7,24,25). Results show no visible surface topographic feature that explains the observed bands; hence, we conclude that they are subsurface reflectors.…”