Fig.15. Residual cemented layer at the upwind of barchan dunes in the north polar region of Mars (source: NASA/JPL/UA) (a)Residual cemented layer in Chasma Boreale(HiRISE PSP_001374_2650_RED,center point:338.95°E,84.95°N; White arrows indicate the locations);(b)Residual cemented layer in the southeast of Olympia Desert(CTX B01_009934_2811_XN_78N226W,center point:134.46°E,79.12°N;Black Arrows indicate the locations);Arrows in the circle of upper right corner represent the wind direction of dune development