ICESAT VALIDATION OF TANDEM-X I-DEMS OVER THE UK

From the latest TanDEM-X mission (bistatic X-Band interferometric SAR), globally consistent Digital Elevation Model (DEM) will be available from 2017, but their accuracy has not yet been fully characterised. This paper presents the methods and implementation of statistical procedures for the validation of the vertical accuracy of TanDEM-X iDEMs at grid-spacing of approximately 12.5m, 30m and 90m based on processed ICESat data over the UK in order to assess their potential extrapolation across the globe. The accuracy of the TanDEM-X iDEM in UK was obtained as follows: against ICESat GLA14 elevation data, TanDEM-X iDEM has 0.028 +/- 3.654m over England and Wales and 0.316 +/- 5.286m over Scotland for 12m, -0.073 +/- 6.575m for 30m, and 0.0225 +/- 9.251m at 90m. Moreover, 90% of all results at the three resolutions of TanDEM-X iDEM data (with a linear error at 90% confidence level) are below 16.2m. These validation results also indicate that derivative topographic parameters (slope, aspect and relief) have a strong effect on the vertical accuracy of the TanDEM-X iDEMs. In high-relief and large slope terrain, large errors and data voids are frequent, and their location is strongly influenced by topography, whilst in the low-to medium-relief and low slope sites, errors are smaller. ICESat derived elevations are heavily influenced by surface slope within the 70m footprint as well as there being slope dependent errors in the TanDEM-X iDEMs.