Figure S1. Example of river cross-section geometry. (a) shows the river center line in red and ICESat-2 global geolocated photon (ATL03) measured heights. (b) shows the exposed topography of the river channel measured by ICESat-2 ALT03 in low-flow seasons, shown in gray points. The solid red line is the smoothed values of ICESat-2 ALT03. The submerged topography is delineated under the assumption that the channel cross-section geometry follows the power law relationship described in (Lawrence, 2007), shown in a solid blue line. The parameters that need to be optimized are submerged depth (distance between ICESat-2 measurements and river bed) and beta (shape parameter).

Figure S2