Design status of a combined Ka-band altimeter/radiometer

In preparation of the post ENVISAT and Jason-2 altimetry missions, Alcatel has completed a phase A study for CNES on a new class of altimeter. A major objective is to propose a combined altimeter and radiometer at minimum cost, size and power consumption compatible with a micro satellite (<100 kg class). The micro-satellite(s) would be used to improve the spatial/temporal sampling of the ocean which is not sufficient for current and future oceanographic missions. The Ka-band (35 GHz) is more interesting than the Ku-band for the altimeter since it improves the link budget and allows larger bandwidth (500 MHz) and pulse repetition frequency (4 kHz). From the scientific point of view, Ka-band altimeter data would give access to a different part of the sea surface roughness spectrum and thus would complement the C+Ku measurements available from other altimeters. The microwave radiometer, used for wet path delay correction, is a dual-frequency instrument (23.8 & 36.8 GHz). The proposed architecture for the Ka-band altimeter is based on the classical deramp technique for pulse compression and it takes benefits of Alcatel and CNES experience from the realisations of Poseidon 1 & 2. The radiometer is of the total power type and is based on direct detection. The altimeter and the radiometer share the same antenna. In parallel of the phase A, breadboarding activities have been started under development in Alcatel on CNES contracts: the transmit power module (2W SSPA) composed of a medium level amplifier, a divider, two high power amplifiers and a combiner. - the signal generator unit (500 MHz bandwidth chirp).