The design of a scanning, spaceborne radar altimeter for measuring polar ice

Radar ice sheet mapping is adversely affected by the slope of the ice surface. Much effort has gone into the correction of the altimeter height measurements and these corrections all involve inferring the surface slope, and possibly curvature, from a series of height measurements. When the surface slopes become as large as the antenna beamwidth, even these methods are not able to recover an accurate height profile. This paper describes the design of a radar altimeter for use in mapping the ice sheet surface. The principle feature of this altimeter is the use of a phased array antenna that allows for steering the transmit and receive beampatterns. Such an altimeter has two advantages over past satellite altimeters. First, it makes possible a direct measurement of the surface slope for correction of the slope induced errors. Second, it can make accurate, pulse-limited height measurements even when the surface slopes become quite large by steering the measurement beam toward the point of first impact with the ice surface