Measuring Velocity of Ice by SRI Using Ascending and Descending Passes

A method of satellite radar interferometry (SRI) enables the remote measurement of three-dimensional velocities of ice flow over large areas of glaciers. At present, ice-flow velocities are measured primarily in situ by use of the Global Positioning System (GPS) in a time-consuming procedure that yields a limited number of data points. In previous efforts to use SRI to determine ice velocities remotely over large areas, measurements were performed along repeat passes. Unfortunately, repeat passes yield data on only the surface displacements associated with the single components of velocity along the radar lines of sight. Moreover, in the absence of additional information, there is no way to separate unambiguously the mixed horizontal and vertical displacement signals acquired via repeat-pass SRI. In contrast, the present method provides three-dimensional velocity data over large areas with horizontal sampling intervals of roughly 100 m.