Derivation of a global land elevation data set from satellite radar altimeter data for topographic mapping

Radar altimeter data from the 336 day cycle of the geodetic phase of ERS-1 has been processed over all land surfaces to produce a consistent, homogeno us data set for topographic mapping purposes. Several processing steps were required to achieve this, the most important of which were waveform retrac king and data filtering. No slope correction was applied to the data as thi s was found not to improve the accuracy. The original radar altimeter data set was 145 Gb in size and a more compact, higher-level product was require d for land topography applications. Three higher-level products were create d: 1) an unaveraged data set comprising elevation, position, backscatter an d a small number of auxiliary parameters; 2) an averaged data set of quasi- regular mean elevations, position, and standard deviation at 5 are min reso lution; 3) a 5 are min digital elevation model interpolated and extrapolate d from the second data set. The accuracy of the radar altimeter data was in vestigated using six point data sets of both global and regional coverage, including airport runway elevations, national geodetic data, gravity statio n heights, and navigation beacon heights. A small number of erroneous eleva tions in both the radar and the point data sets were identified. After remo ving outliers with a difference of greater than 300 m the mean difference b etween the radar and point data was -0.5 m +/- 44 m full width at half maxi mum.