Global analysis of multi-mission echoes over the earth’s land surface from 15 years of altimeter missions
Monica Dowson(1) and Philippa A.M. Berry(1)
De Montfort University,
Faculty of Computer Sciences and Engineering,
Leicester LE1 9BH,
A vast quantity of radar altimeter echoes have been collected over the earth’s land surfaces by the series of missions flown over the past fifteen years. Although primarily designed for operation over ocean, a significant part of the earth’s continental land mass has also been sampled, even by those missions specifically configured for ocean operation (Topex and Jason-1). The additional mode of operation of ERS-1 and ERS-2 altimeters enabled sampling over much of the earth’s land surfaces, whilst the multi-mode capability of the Envisat RA-2 has given us the first almost universal surface echo database (except for very extreme terrain such as the highest reaches of the Himalayas). The totality of these missions has resulted in a unique global database of echoes, containing information not only on the elevation but also on the surface characteristics.
This paper presents the results of a global analysis of echoes from all these missions, interpreted using a rule-based expert system, and discusses the information which can be extracted, both from the spatial distribution and from the temporal changes. A series of examples is presented, illustrating the characteristic signatures of different terrain types, and discussing the impact on echo shape of roughness on different spatial scales.
The key role of surface water in temporal change is highlighted, including the sporadic effects from ephemeral events, and the seasonal and interannual changes of inland water and snow. The results demonstrate the unique contribution of this global dataset to measurement and monitoring of the earth’s land surfaces.