Sea ice motion measurements from SEASAT SAR images

Abstract

Satellite imaging radar is expected to become the prime instrument for mapping the distribution and motion of sea ice on a periodic basis, The observational independence from weather, fog, and clouds and the fact that it provides its own illumination are decisive advantages that imaging radar has in the remote sensing of sea ice. The SEASAT spacecraft launched in 1978 included such an imaging radar, and approximately one fourth of all SEASAT SAR observations are of sea ice in the Beaufort Sea. Data from seven sequential orbits of the satellite were selected to study the capabilities and limitations of spaceborne radar application to sea‐ice mapping. The results are encouraging: (1) There is no difficulty in identifying homologue ice features on sequential radar images; (2) The accuracy is entirely controlled by accuracy of the orbit data and the geometric calibration of the sensor; (3) Conventional radargrammetric methods serve well for satellite radar ice mapping; (4) Ground control points can be used to calibrate the ice location and motion measurements in the cases where orbit data and sensor calibration are lacking. Ice motion was found to be approximately 6.4±0.5 km per day. However, higher accuracies are feasible with better timing calibration of the sensor events and knowledge of the orbit. The accuracy of pixel location was also determined over land areas. It was found that with the use of one control point in 10,000 km2 the accuracy is about ±150 m. With higher density of control points (7 in 1000km2) the location accuracy improves to the image resolution (i.e., ±25 m). This is applicable for both optical and digital data.