On the use of GPS / inertial exterior orientation parameters in airborne photogrammetry

Within the last five years extensive research was done using integrated GPS/inertial systems for the direct georeferencing of airborne sensors for high-end applications. Pushed by the development and practical use of digital sensor systems, originally started with laser scanner systems and followed by imaging multi-line pushbroom scanners, direct georeferencing offers the only way for an efficient sensor orientation process. Nonetheless, even for standard frame based camera systems, digital or analogue, the use of direct orientation measurements is useful in especially in – from a photogrammetric point of view – unfavourable applications like corridor surveys or single model orientation. In the ideal case using direct exterior orientation elements with sufficient accuracy image orientation without any ground control is possible. Within this paper the use of integrated systems in airborne environments is discussed, where the main emphasis is laid on the combination with standard analogue frame cameras. The empirical results of different well controlled test flights are used to illustrate the today's performance of direct georeferencing based on high-end integrated systems. Additionally, a combined GPS/inertial-AT or integrated sensor orientation approach is presented which allows the in-situ calibration of certain system parameters even without ground control and therefore provides highest flexibility to overcome the most limiting factor of direct georeferencing: uncorrected errors in the overall system calibration. Finally, the use of directly measured exterior orientations in model orientation and DEM generation is investigated.