Interferometric estimation of three-dimensional ice-flow using ascending and descending passes

Satellite radar interferometry (SRI) provides an important new tool for determining ice-flow velocity. Interferometric measurements made from a single-track direction are sensitive only to a single component of the three-component velocity vector. Observations from along three different track directions would allow the full velocity vector to be determined. A north/south-looking synthetic aperture radar (SAR) could provide these observations over large portions of the globe, but not over large areas of the polar ice sheets. We develop and demonstrate a technique that allows the three-component velocity vector to be estimated from data acquired along two track directions (ascending and descending) under a surfaceparallel flow assumption. This technique requires that we have accurate estimates of the surface slope, which we also determined interferometrically. To demonstrate the technique, we estimate the three-component velocity field for the Ryder Glacier, Greenland. Our results are promising, although we do not have yet ground-truth data with which to determine the accuracy of our estimates.