A Fully Digital System For Airborne Mapping

This paper describes the development and preliminary testing of a multi-sensor fully digital system for remote sensing, digital mapping, and GIS applications. This system was developed at the University of Calgary in collaboration with the University of California at Berkeley, with aircraft and logistics support by HJW Inc., CA. It integrates a medium class INS, two low-cost GPS receivers, and a high resolution digital camera. The digital camera captures strips of overlapping vertical images. Camera exposure stations and INS records are time-tagged in real time by the GPS pulse. The INS/GPS real time discrete measurements allow for the determination of the six independent parameters describing the motion of the carrier aircraft which are directly related to the problem of exterior orientation. During post-processing, image exterior orientation information is extracted from the INS/GPS-derived trajectory. Ultimately, this configuration will eliminate the need for ground control in airborne mapping. Flight tests were done over a part of the university campus at Berkeley which had ground control points of sufficient accuracy. A strip photography approach was followed to test the integrated system performance and to allow for in-flight calibration of the entire system. The low-cost GPS receivers were tested in both static and kinematic modes in Calgary. Also, the digital camera was calibrated at the University of Calgary. System calibration results are presented in some detail. The concept of direct georeferencing of digital images without ground control is highlighted. The potential of a low-cost IMU will be addressed. In addition, the potential of the new system for photogrammetric use will be addressed. The major applications of such a system will be photo ecometrics, mapping of utility lines, roads, pipelines, and the generation of digital elevation models for engineering applications.