Intensity of Satellite Radar-Altimeter Return Power Over Continental Ice: A Potential Measurement of Katabatic Wind Intensity

We analyse, above continental ice, the various factors which affect the power return of the Seasat radar altimeter as measured by its Automatic Gain Control (AGC). Corrections of effects due to the AGC loop control are first applied. AGC is then normalized by positioning the half-power point at the middle of the instrument receiving window. This operation is valid for both surface and volume scattering. Over a part of Antarctica between long. 90° and 150°E., the remaining variations of AGC are of the order of 15 dB. Most of these variations occur on a large scale (>100km) and are correlated with the katabatic wind intensity. This indicates that AGC measures either surface roughness of the ice, which is related to wind intensity, or grain-size which could also be dependent on the wind.In-situmeasurements support the evidence that the radar altimeter is more sensitive to surface scattering. These data could therefore provide a measurement of the intensity of katabatic winds over the continental ice.