Based upon the development and flight experiments of the airborne radar altimeter

and according to the characteristics of the signal returned from ocean surface

a spaceborne radar altimeter system is designed. The system operates on pulse limited mode

transmitting pulses are FM Chirp pulses

the returned signal is processed in receiver in frequency domain instead of time domain by adopting “Full De ramp” technique and frequency spectrum analysis method. Adaptive tracker can remove about 75% of the noise power. High pulse repetition rate results in maximum effective number of independent pulses and are best effective in eliminating ocean surface backscatter speckle noise. The main operating modes are desiged: dual resolusion acquisition and tracking mode makes acquisition time of the returned signal within 5 s

calibration mode can assure the designed height precision. The effects to height evaluation of the main noises

i.e. ocean surface backscatter speckle noise and receiver thermal noise

are analyzed. By analyzing the returned signals of several typical sea states

the results have shown that the system height measurement precision can be ±2cm.