A Ka-band altimeter for future altimetry missions

In preparation of the post ENVISAT and Jason-2 altimetry missions, CNES and Alcatel are currently investigating the feasibility of a new class of altimeter. A major objective is to propose an instrument at a minimum cost and size which can be accommodated equally on micro satellites (/spl sim/50 kg) and on larger satellites such as Jason. 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. Although the C+Ku-band Poseidon-2 altimeter to be flown on Jason-1 has a moderate mass and power consumption, it is not directly compatible with a micro-satellite limited resources. For a given antenna size, limited to about 60 cm for a micro satellite, the Ka band (/spl sim/35 GHz) is a more interesting candidate than the Ku band in order to improve the link budget. From the scientific point of view, Ka-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 on board the same or a different platform. This paper presents the altimeter concept and the required performances. The proposed concept is a Ka-band altimeter with a high vertical accuracy (0.3 m) based on the classical deramp technique for pulse compression. A particular attention is given to the analysis of the propagation losses due to atmospheric gazes, clouds and rain. The preliminary design of the altimeter is described and mass and power consumption budgets are given. A preliminary assessment of the elevation accuracy over ocean is discussed.