Remote Sensing Series Vol. 13

K. Christoph Graf - 1988
Verwendung geodätischer Abbildungen bei der Geocodierung von Satelliten-Bilder

Summary

In recent years aerial and satellite images have become an essential tool for a continuous monitoring of the complex processes on the earth's surface. The generated images prove most valuable when they share the geometry which is used for maps of the represented area. The objective of this study was to establish a procedure which allows geocoding of spaceborne SAR-images for the same projection systems which the national surveys use for topographic mapping.

For this purpose it is necessary to establish a precise relation between the map's coordinate system and the geocentric coordinate system of the satellite. Two aspects have to be considered:

1) the specific map projection system of the selected country and 2) the geodetic datum which defines the basis of a map.

The accuracy of the transformation was tested in the bordering areas of Switzerland, Germany and France. The coordinate shift for a series of control points amounts to less than an average of Sm when the geodetic datum is considered at the transition from one country's geodetic projection to the one of a neighbouring country. Therefore the shift lies below the image pixel resolution of todays spaceborne remote sensing devices. Shifts up to several pixels can occur if the geodetic datum is neglected.

Due to the very satisfying results of the coordinate-transformation of isolated points from one national map projection system to a neighbouring system a digital elevation model with French map coordinates was transformed into the German Gauss-Kruger system. Afterwards it was connected to an existing model in the GaussKruger coordinates. Finally, two SIR-B image scenes (Shuttle Imaging Radar) from the Kaiserstuhl area (FRG) were geocoded for the German Gauss-Kruger system. Therefore the elevation model mentioned above was necessary.

The applied modular transformation method allows a problem-free transition between different national map projection systems or geographic coordinate systems. Considering the geodetic datum during the transformation, the accuracy required for remote sensing applications can easily be reached. The transformation modules established can even be applied unchanged for the geocoding using no ground control points of images from optical sensors.