Structured Sun glitter recorded in an ASTER along‐track stereo image of Nam Co Lake (Tibet): An interpretation based on supercritical flow over a lake floor depression

Sun glitter and synthetic aperture radar (SAR) remote sensing techniques that respond to the small‐scale textural roughness of water surfaces often reveal a plethora of signatures indicative of the presence of bed formations submerged in shallow water (of depth <30 m), even though the electromagnetic signals employed in such methods are reflected at or near to the water surface. In homogeneous (nonstratified) regimes, these signatures are interpreted on the basis of a causal sequence involving an initial topography‐induced perturbation to a strong background current (of speed nominally >0.4 m s −1 ), the subsequent formation of surface current gradients (the “straining”) of order 10 −3 s −1 , and an ensuing local modulation of the centimeter‐scale surface roughness controlling the scattering of both light and radar. Here we consider how the presence of stratification might influence this generative sequence in an analysis of high‐sensitivity Sun glitter observations gathered when the background flow speed and surface current gradients are at least one order of magnitude lower. The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) acquired these observations on 22 July 2001 while imaging in along‐track stereo mode from slanted fields of view that encompassed Sun glitter reflected from the surface of Nam Co, a large Tibetan lake that is free from anthropogenic surface‐slick contamination. We interpret a structured Sun glitter feature appearing within a shallow embayment in the northwest of the lake as the surface roughness manifestation of a wake formed by supercritical stratified flow over a localized depression in the lake floor topography.