Geodetic Application Of ERS-1 Altimeter Data Over Land
The high number of valid returns obtained over land from the ERS-1 altimeter during the geodetic mission presents a unique opportunity for orthometric height determination. In order to utilise these data fully, the precision to which altimeter derived heights can be generated over land surfaces must first be quantified. In this paper, retracked Altimeter Waveform Product (WAP) (7) data from the Geodetic Mission of ERS-1 are evaluated. The dataset upon which this research is based has been derived from the WAP dataset via the use of an Expert System which ‘retracks’ each altimeter waveform return, selecting one of a set of retracking algorithms designed to optimise the determination of the individual height. The resulting data at a number of test sites over four continents have been used to investigate the extent to which retracked altimeter data can be used to generate Ground Control Points for geodetic purposes.
The results obtained over these test areas demonstrate that altimeter heights over land can be determined with very high internal consistency, with between 20% and 50% of results in a 15° square agreeing to within 1m, and filtering for specific retracker types the percentage can be as high as 60%. However, interpretation of the complex echoes returned over areas of significant topographic relief necessitates the use of a sophisticated processing chain in order to generate optimal height values. This paper presents sample results and discussion drawing on the results from the test areas to infer the potential for generation of geodetic control points on a global scale.
KeywordsTest Area Altimeter Data Geoid Model Orthometric Height Terrain Type
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