Synthetic Spotlight Sar Image Generation to Improve Geopositioning Accuracy

Many applications require the ability to use airborne sensor data to perform accurate geopositioning. Synthetic Aperture Radar’s (SAR) ability to image from long distances and in poor weather makes it advantageous for such geopositioning. However, the ability to accurately position using SAR data is reliant on having accurate sensor support data (sensor position, velocity, etc...). This paper examines the ability to use synthetic spotlight SAR images to refine and improve the SAR support data and therefore improve the positioning accuracy. It begins by reviewing the methods used to generate the synthetic image from a high resolution terrain information (HRTI) digital elevation model (DEM). It describes how the algorithms account for the unique image layover and shadowing characteristics of spotlight SAR images. It also describes the calculation of backscatter values and performance of SAR single ray intersections with the terrain surface. Sample SAR images generated from a DEM are presented for comparison to actual SAR data of the same area. The goal is to use the HRTI as a control source. The actual SAR image will be registered to the synthetic SAR, which is generated from the HRTI, and the results of this registration will be used to refine the sensor support data for the actual image. The refined support data will in turn provide improved geo-positioning accuracy. Although further research is required, the results of these methods to date are promising for future utility.