Study of a constellation of bistatic radar altimeters for mesoscale ocean applications

A constellation of satellite radar altimeters for mesoscale ocean applications has been recommended since the beginning of this decade. Studies show that eight monostatic satellites are needed to achieve an ideal sample spacing of seven days revisit time and 50-km spatial sampling. However, for this number of satellites the required cost of such a constellation is very high. With the appearance of Global Navigation Satellite Systems (GNSS), such as GPS and GLONASS, there is a great opportunity for constellations of small satellites to operate in a cooperative bistatic way, i.e., with their sensors synchronized both in time and space. The benefits of this concept are the subject of this paper. In this article, the authors study a constellation of bistatic altimeters with fewer satellites than the monostatic constellation but with the same sampling performance. This paper first introduces the mesoscale ocean requirements. The configuration of the bistatic constellation follows together with an analysis of its coverage and required pulse-limited footprints. Suitable gate lengths, pulse repetition frequency, synchronization, pointing requirements, and link budget are discussed. The tracker and estimation process are also described as well as calibration issues. The goal of the whole design of the altimeter instrument itself has been to achieve simultaneous monostatic and bistatic operation with the simplest architecture