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.