Accurate geo-referencing and DSM generation with HRSI

Outlook

High Resolution Satellite Images (HRSI) are used in a wide range of applications and by users from different disciplines. With the increasing spatial resolutions, the HRSI can meet requirements of many new applications where accurate geographical information is necessary. The temporal resolutions of the sensors are improved with extended viewing and tilting capabilities. The average revisit times of the satellites are also increasing, making them applicable even for many disaster management and process monitoring applications. Thus the HRSI provide efficient data sources for mapping, GIS database updating, change detection, and environmental monitoring applications.

3D mapping is becoming a buzzword in the geospatial community. However, in an earlier contribution in this Magazine we have pointed out that neither the goals nor the procedures of 3D mapping are clearly defined yet. The available new technologies require a totally fresh approach to mapping.

Figure 3: View on the DSM of Arequipa, Peru, derived from a Worldview-1 stereo with SAT -PP

For efficient utilization of this kind of images, accurate geometric processing is needed. Our software package SATPP is a powerful and flexible tool for accurate and automatic 3D processing of high-resolution satellite images. It has already been tested in many projects using the imagery of different high-resolution sensors. The specially designed matching component for the imagery of the Linear Array CCD sensors is especially powerful for producing high-quality DSMs, in terms

of accuracy and completeness. Functions like ortho-image generation, monoplotting and feature extraction are also available. When used together with the CyberCity ModelerTM, 3D city models can be produced efficiently from the images of very high resolution satellite sensors, such as IKONOS, Quickbird, WorldView-1 and others to be expected in the future.

Satellite images are an interesting source for 3D mapping. However, they still do have a number of substantial disadvantages when compared to aerial images. In our tests with manual mapping from IKONOS stereo images we found that IKONOS images were not sufficient for the production of 1:25,000 map data. But even if we consider that satellite images are already now available at the same spatial resolution as aerial images (WorldView-1 with 0.5 m GSD) we still have to take into account the lower radiometric quality of satellite data. When compared to aerial images the ground Sampling Distance (GSD) should not be taken as the only parameter. Especially digital aerial images provide us with a hitherto unsurpassed image quality, which is very crucial when it comes to the interpretation of map features.

However, these statements refer to the map specifications of Switzerland. In other countries these specifications may not be as stringent.

References

Gruen, A., Wolff, K, 2008. 3D mapping from space? Coordinates, Vol. IV, Issue 7, July 2008, pp. 18-24

Kocaman, S., Gruen, A., 2008: Geometric modeling and validation of ALOS/PRISM imagery and products. International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol.37, Part B1-2, pp. 731-738

Kocaman, S., Woff, K., Gruen, A., Baltsavias, E., 2008: Geometric validation of Cartosat-1 imagery. International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol. 37, Part B1, pp. 1363-1368

Wolff, K, Gruen, A., 2008: Up-to-date DSM generation using highresolution satellite image data. International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol.37, B1-3, pp. 1103-1108

Zhang, L., Gruen, A., 2006. Multiimage matching for DSM generation from IKONOS imagery. ISPRS Journal of Photogrammetry and Remote

Sensing, Vol. 60, pp. 195-211