Two decades of land altimetry – achievements and challenges
Philippa A. Berry(1)
De Montfort University,
Leicester LE1 9BH,
Studies of altimetry over land began with data from SeaSat and Geosat Since this initial work, huge advances have been made both in instrument design and in interpretation of the complex and rapidly varying echoes returned from topographic surfaces. This paper presents an overview of the achievements in land altimetry, drawing on the vast database of echoes returned by Geosat, ERS-1, ERS-2, Topex, Jason-1, Envisat and GFO, including an assessment of the key contribution over rough terrain of the RA-1 and RA-2.
Data collected over the earth’s land surfaces have been used for a range of applications, primarily for topographic mapping and measurement of inland water heights. In mapping, data from the ERS-1 Geodetic Mission allowed the derivation of a new Global Digital Terrain Model, ACE. More recently, data from all altimeters have a key role in assessment and correction of the Shuttle Radar Topographic Mission dataset. Over inland water, the different orbit repeat patterns, combined with the instrument designs, have given access to data over a huge range of targets. Land radar altimeter data have a range of further applications, from identification of temporally changing information such as snow cover and flooding, to derivation of detailed backscatter models for calibration of both existing and future altimeters, including instruments optimised for measurement of clouds. The range of applications continues to grow, with potential additional applications such as soil surface moisture.
The unique continuous time series of echoes still contains information not yet identified and extracted; the RA-2 I.E. capability and the CryoSat mission have the potential to give further new insights, not only enabling data from these missions to be utilised fully, but also permitting the identification of further information encoded within the continuous database of altimeter echoes.
Although an instrument originally designed for operation over the earth’s oceans, the radar altimeter has made a huge contribution to our understanding of the earth’s land surfaces and climate related processes. With the only planned future altimeter mission currently being Jason-2, there is a very real prospect that the continuity of this valuable time series may be lost.