Abstract
Abstract. 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 12.5 m, 30 m and 90 m 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±3.654 m over England and Wales and 0.316 ± 5.286 m over Scotland for 12 m, −0.073 ± 6.575 m for 30 m, and 0.0225 ± 9.251 m at 90 m. Moreover, 90 % of all results at the three resolutions of TanDEM-X iDEM data (with a linear error at 90 % confidence level) are below 16.2 m. 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 70 m footprint as well as there being slope dependent errors in the TanDEM-X iDEMs.
Highlights
For some 30% of the Earth’s land surface, downstream processing of EO data over land for applications in land and atmospheric retrieval require corrections for topographic relief and/or slope and aspect
As spatial resolution of the VIS/IR/SAR images increases, so does the need to improve Digital Elevation Model (DEM) spatial resolution and accuracy. Such global DEMs are being produced from spaceborne EO sensors, such as from SAR (SRTM, TerraSARX and TanDEM-X), stereophotogrammetry (ASTER, SPOT, PRISM and IRS-3P) and lidar (ICESat) (Farr, Rosen et al 2007, Wang, Cheng et al 2011, Fujisada, Urai et al 2012)
The accuracy results are shown in the Tables below. These Tables summarize the discrepancies between DEMs and ICESat GLAS14 data
Summary
For some 30% of the Earth’s land surface, downstream processing of EO data over land (and some continental shelves) for applications in land and atmospheric retrieval require corrections for topographic relief and/or slope and aspect. All three types may be reduced in magnitude by refinements in technique and precision, they cannot be completely eliminated (Caruso 1987, Brown and Bara 1994). These DEM errors are elusive and constitute uncertainty (Wechsler 2007). Techniques to quantify DEM uncertainty are not readily available nor are they systematically applied to DEM data applications. It is critical to validate DEM products for public users over large geographic areas (Gesch 1994, Danielson and Gesch 2011)
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