PhotoSat Information Ltd. is a Canadian service provider specializing in producing satellite image technology services for companies working with land resources. PhotoSat's newest application creates high resolution digital elevation model (DEM) data for construction, mining, and other terrain oriented projects. PhotoSat's application developments have brought these services into the market with lower costs than former approaches for gathering this data. The PhotoSat system starts the processing by testing small areas from each of the sets of stereo photos to determine the preferred processing characteristics for that exact combination of territory type and satellite camera look directions. For example, in mountainous areas, a combination of a satellite image looking straight down with a second satellite image looking at thirty degrees off vertical uses a different set of preferred processing characteristics than two satellite images looking from different directions, both at thirty degrees from vertical. An additional important factor in choosing processing preferred characteristics is the direction of the sun with respect to the predominant grain of the topography. Just like in seismic processing systems, the PhotoSat processor quickly understands the types of processing characteristics which are most likely to give the best results in specific types of terrain with different satellite camera look directions. Once the processing characteristics are chosen, the elevation surface for the entire satellite image stereo photos are automatically processed using these characteristics. This is analogous to running interactive processing tests on small portions of a seismic survey to recognize the processing characteristics prior to automatically processing the entire seismic survey. When the automatic elevation processing is finished, the satellite photos used to create the elevation surface should match precisely. The PhotoSat processor uses both automatic and visual checks to recognize how close is the match between the shots. Using the photos as alternate frames in a movie is one effective visual check of the closeness of the match. When the elevation surface is correct and the photos match exactly there is no apparent movement in this movie. The processor often runs this movie at each processing cycle while they are choosing the preferred processing characteristics. The majority of PhotoSat's stereo satellite processing of these digital elevation models is performed in the wavenumber domain rather than in the spatial domain. The PhotoSat stereo satellite processing system makes extensive use of Fourier transforms, including Non Equidistant Fourier Transforms, Fast Fourier Transforms, and Discrete Fourier Transforms to map the satellite photo data from the spatial to the wavenumber domain. These processes are computationally intensive. Recent advances in computer hardware, especially the availability of the massively parallel Graphics Processing Units (GPUs) has made this kind of processing cost effective for stereo satellite photos.
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PhotoSat Information Ltd. is a Canadian service provider specializing in producing satellite image technology services for companies working with land resources. PhotoSat's newest application creates high resolution digital elevation model (DEM) data for construction, mining, and other terrain orient
Gerry Mitchell is a Professional Geoscientist and Geophysicist in Canada. As President of PhotoSat Information Ltd., he has led the development of PhotoSat's new digital elevation model (DEM) production application.
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