SZ-4 Radar Altimeter and Its Measurement Results on Orbit
SZ-4雷达高度计及其在轨测量结果

SZ-4 radar altimeter,the first China's spaceborne experimental radar altimeter launched on Dec.30th 2002,had obtained plenty of scientific data according to the pre-designed operational modes.In this paper,the system scheme,the system realization,and the measurement results of SZ-4 radar altimeter are introduced.As the key technologies,the sea echo model which describes the scattering course of altimeter,the full de-ramp process which realizes the pulse compress for the high resolution,and the maximum likelihood estimation which performs the tracking algorithm on board are discussed in detail.The characteristics for SZ-4 altimeter hardware system are outlined,and the RF unit and the digital processing unit of this altimeter are also introduced.This paper discusses the operation modes on orbit for SZ-4 altimeter,which are bias/noise measurement,inner calibration,acquisition,tracking,communication with satellite host,data transfers,and instrument status detection.Because the altimeter and the scatterometer installed on SZ-4 worked by turn due to the power limit,the obtained data of altimeter were not consecutive.This non-consecutive observation restricts the application of the altimeter.The significant wave heights are obtained from the data on Feb.8th 2003,and the results were similar to that of the ERS-2.From these results,we can conclude that this experiment on orbit had validated the function of the SZ-4 altimeter,and it would be a great contribution to the China's future Seasat.