Assessment of Multi-source Remote Sensing DEMs with RTK-GPS and Levelling Surveys

High resolution digital elevation models (DEMs) have been used in many applications such as civic planning, military mapping and navigation, natural hazard risk assessment, to name only a few. It has been a long history of using photogrammetry and dense ground surveys to draw the contour lines of the terrain and create the elevation model. Nowadays high precision DEMs with the vertical resolution from several meters to several centimeters can be derived using various remote sensing techniques, such as photogrammetry, radar interferometry, airborne laser scanning (ALS) and high resolution space imaging. Ground control points (GCPs) that are normally obtained using traditional surveying methods and Global Positioning System (GPS) are used for DEM calibration and validation. This paper demonstrated the use of realtime kinematic GPS (RTK-GPS) to measure the elevation of terrain over an open unobstructed area, together with traditional levelling survey data for validating various high precision DEMs. One photogrammetric DEM with 1 arc-second resolution, two repeat-pass interferometric synthetic aperture radar (InSAR) DEMs derived from both Cand L-band satellite data, the C-band Shuttle Radar Topography Mission (SRTM) DEM and lastly a ALS DEM were compared against the RTK-GPS and levelling surveys. The results showed that ALS DEM has the highest height accuracy with a RMS error of less than 0.2m, followed by photogrammetric and SRTM DEMs with the RMS errors of less than 7m and 12m respectively. Finally the repeatpass InSAR DEMs have the RMS errors between 10~30m. The sensitivity of C-band InSAR DEM to the vegetation can also be identified in the results.