A transponder system dedicating for the on-orbit calibration of China's new-generation satellite altimeter and scatterometer
In this paper a transponder system dedicating for the on-orbit calibration of the two primary active microwave sensors: radar altimeter and radar scatterometer are designed. The three major parameters: the height measured by the altimeter, and the backscattering coefficient measured by the altimeter and the scatterometer can be fulfilled in the same system. The transponders proposed in this paper is a pulse-regenerator, which can down-converted the altimeter/ scatterometer Radio Frequency (RF) signal to the baseband and record the digital samples, then regenerate a “modulated” signal which is to the altimeter/ scatterometer receiver. The power, triggering time and the modulation are all adaptive, so the transponder has much greater flexibility than the conventional bent-pipe (pulse-repeated) transponder, which only offer simple time-delay or attenuation / amplification at the RF stage. In this paper the backgrounds are reviewed, the implementations of a new transponder system are introduced, and the calibration rationales are described. Particularly, the configuration of three transponders is optimized to exploit the potential of the new technology.