Comparison of satellite imagery DEMs produced using photogrammetry and radargrammetry techniques

The aim of this study is to evaluate the quality of middle resolution radargrammetric DEMs produced from high resolution satellite SAR images, in comparison with photogrammetric DEMs from optical satellite data. The Salento Peninsula (Southern Italy) was chosen as a test site. A SPOT Pan stereopair acquired in 1996 and a Radarsat Fine mode stereopair acquired in 1998 were used. A 10 meter resolution DEM was generated from the SPOT images using digital photogrammetry and automatic image matching. Radarsat images were resampled to 10 meter resolution prior to DEM generation. The quality of the SPOT and Radarsat DEMs were benchmarked against two other DEMs: the first generated by linear interpolation of the official digital contour map of Italy at 1:25,000 scale, and the second a resampled 3-arc-second Shuttle Radar Topography Mission (SRTM) DEM. An error map was created for each DEM. A visual and statistical analysis of the errors highlights the fair level of overall accuracy, with acceptable RMS error values, of the radargrammetry DEM. However, this DEM is severely affected by noise, probably caused by radar speckle, and generally smooths out morphologic details such as steep escarpments. The results of this study confirm the applicability of radargrammetry for middle resolution DEMs. This technique can be effectively applied in areas where high precision and accuracy are not needed, or where it is difficult to acquire optical images for traditional photogrammetry due to extreme weather conditions. Keywords-photogrammetry; radargrammetry; satellite imagery; DEM.