Close-up view of the area of interest from (a) the original radargram with normalised echo strength, (b) the radargram with the log-Gabor filter applied, (c) the MOLA cluttergram, and (d) the HRSC cluttergram. The red, yellow, and green ovals show each of the three sets of unusual subsurface layers. In the green oval, the red solid line spans from Cols. 53 to 68, and the red dotted line ranges from Cols. 69 to 82.