A Novel Technique for the Automatic Detection of Surface Clutter Returns in Radar Sounder Data

One of the most critical problems that affect the analysis of orbiting radar sounder data is the presence of spurious surface clutter returns. These are due to off-nadir echoes related to surface topography which may be detected as (or mask) actual subsurface targets. The detection of such returns is usually carried out manually through a visual comparison between actual radargrams and surface clutter simulations obtained using available digital elevation models (DEMs). This is an inherently subjective and time-consuming task, which may reduce the scientific return of the data. In this paper, we address this problem by proposing a novel technique for the automatic detection of surface clutter returns in radar sounder data. The proposed method is made up of three steps: 1) the simulation of surface clutter returns using available DEMs; 2) the automatic coregistration between radargrams and simulations; and 3) the extraction of surface clutter returns from the coregistered radargrams. The coregistration step is performed in two phases: 1) a coarse registration based on the detection of the first return line on both input radargrams and 2) a fine registration based on B-spline deformation. The proposed technique is robust to radargram geometric deformations (e.g., due to ionospheric effects) and allows the generation of different types of outputs (e.g., coregistered simulations, binary clutter maps, and false-color compositions) that can both greatly support the scientific community in the manual analyses of radar sounder data and drive the development of reliable automatic methods for high level processing. The effectiveness of the proposed method is proven on two data sets acquired on different areas of Mars by the Shallow Radar instrument.