COMPARISON OF DEMS FROM STAR-3i INTERFEROMETRIC SAR AND SCANNING LASER

Within the past few years there has been a significant increase in the use of Digital Elevation Models (DEMs), for applications as varied as telecommunications and precision agriculture, forestry and flood-risk assessment. Additionally, one may expect that externally-supplied DEMs will be used increasingly for ortho-rectification of high-resolution satellite imagery as it becomes available. There are now available several technologies from which DEMs may be created, with varying degrees of detail, accuracy, associated cost and availability. In both North America and Europe, government agencies have traditionally provided mapping products, including derived DEMs, to the public. However, the applications noted above are expected to require increasing detail beyond what these government sources currently provide. Three technologies that are currently creating DEMs at increased levels of detail include (1) soft-copy photogrammetry using stereo air-photo, (2) scanning airborne laser or lidar and (3) interferometric airborne radar. In this paper we examine the capabilities and deficiencies of two of these DEM sources – airborne laser scanning systems and interferometric airborne radar. STAR-3i is an airborne interferometric SAR system carried in a Lear jet and operated by Intermap Technologies Corporation. In the past two and a half years of commercial operation, DEMs have been acquired for several hundred thousand km on several continents. At the same time, several companies have been creating DEMs over smaller areas using airborne laser scanning systems, and comparative data sets are now becoming available. In this paper, the comparative DEM performance of these two technologies will be demonstrated with respect to three application areas of interest: (i) bald-earth performance for flood-plain risk analysis, (ii) building height extraction in urban areas, and (iii) forested and agricultural areas with respect to vegetation issues. In these examples, the laser-derived DEMs are treated as truth at the 15 cm (1 sigma) level. The radar-derived DEMs, created on a 5 meter grid, are shown to exhibit a ‘noise floor’ at the 35 cm (1 sigma) level for typical operational altitudes in non-urban bald-earth environments. While the performance is not as strong as that of the laser systems, there are obvious cost and schedule advantages where large area coverage is required. These will be addressed. It is concluded that the technologies tend to provide complementary rather than competitive solutions for many applications.