From Figs. 1(a) and 1(b), three sites, labeled A, B, and C from west to east, were selected for water depth inversion. The profiles of image values (the pixel gray values) in the NVI and the BVI are plotted in Fig. 3, which shows that the curve trends for the NVI are almost exactly opposite to the BVI trends, indicating the brightness reversal due to the different view angles. For site A, the image values vary from 15.5 to 23.3 in the NVI, and from 5.2 to 9.5 in the BVI. Average values are 18.9 and 7.2 for the NVI and BVI, respectively. For site B, the average image values increase to 22.4 in the NVI and 7.4 in the BVI, and the image values vary from 19.0 to 26.7, and from 6.0 to 9.5 in the NVI and BVI, respectively. For site C, the average image values further increase to 28.3 in the NVI and 7.8 in the BVI, and the image values range from 23.3 to 34.5 in the NVI, and from 6.0 to 10.3 in the BVI. Thus, the average image values increase significantly from west to east in the NVI, varying by c. 50% (from 18.9 to 28.3), implying that the sand waves at the east site are more easily distinguished than those at the west site. However, no significant variations are seen in the BVI results from the three sites.