Two-sided long baseline radargrammetry from ascending-descending orbits with application to mapping post-seismic topography in the west Sichuan foreland basin

Abstract

One-sided ascending or descending Synthetic Aperture Radar (SAR) stereo-radargrammetry has limited accuracy of topographic mapping due to the short spatial baseline (~100 km) and small intersection angle. In order to improve the performance and reliability of generating digital elevation model (DEM) from spaceborne SAR radargrammetry, an exploration of two-sided stereo-radargrammetry from the combination of ascending and descending orbits with geometric configuration of long spatial baseline (~1000 km) was conducted in this study. The slant-range geometry between SAR sensors to the earth surface and the Doppler positioning equations were employed to establish the stereoscopic intersection model. The measurement uncertainty of two-sided radargrammetric elevation was estimated on the basis of radar parallax of homogeneous points between input SAR images. Two stereo-pairs of ALOS/PALSAR (Advanced Land Observing Satellite/Phased Array type L-band Synthetic Aperture Radar) acquisitions with the orbital separation almost 1080 km over the west Sichuan foreland basin with rolling topography in southwestern China were employed in the study to obtain the up-to-date terrain data after the 2008 Wenchuan earthquake that hit this area. The quantitative accuracy assessment of two-sided radargrammetric DEM was performed with reference to field GPS observations. The experimental results show that the elevation accuracy reaches 5.5 m without ground control points (GCPs) used, and the accuracy is further improved to 1.5 m with only one GPS GCP used as the least constraint. The theoretical analysis and testing results demonstrate that the two-sided long baseline SAR radargrammetry from the ascending and descending orbits can be a very promising technical alternative for large-area and high accuracy topographic mapping.