A novel approach for absolute backscatter calibration of spaceborne altimeters

The issue of the backscatter calibration of radar altimeters has been raised only recently. This paper presents a novel method based on the assumption that the dominant unknown is the instrument receiver gain. This assumption is based on the relatively extensive testing and characterization done preflight on ESA instruments, and on the operational experience done with ERS. The receiver gain calibration is based on a similar technique as the spaceborne radiometers, and assumes that the altimeter can measure the environment noise level. An ad-hoc test on this latter issue was done recently on the ERS-1 altimeter in the framework of the preparation to the ENVISAT mission.