Engineering design of the rain mode on an ocean-dedicating radar altimeter

Satellite radar altimeters are fundamental tools in microwave remote sensing, but traditionally they were regarded as unsuitable for rain measurement. This paper designs a rain mode on an ocean-dedicating altimeter, taking China´s forthcoming HY-2 ALT as a typical example. In rain mode the altimeter receives the surface and rain echoes simultaneously, so it can estimate the rain layer structure without losing surface topography information. The variable system parameters are designed to fulfill the task with very low hardware expenses. Some key issues are discussed in detail. To achieve the compatibility of measuring both surface and rain, an adaptive digital i/q demodulator is proposed, and receiver weighting is implemented to suppress the side-lobes. Constrained by echo power, altimeter can detect rains heavier than 6 mm/hr.