Extraction of topography from side-looking satellite systems—A case study with SPOT simulation data

A test site in the Cape Flattery area of northwest Washington state was selected for constructing a simulated data set to evaluate techniques for extracting topography from side-looking satellite systems. A negative transparency orthophotoquad was digitized at a spacing of 85 μm, resulting in an equivalent ground distance of 9.86 m between pixels and a radiometric resolution of 256 levels. A bilinear interpolation was performed on U.S. Geological Survey digital elevation model (DEM) data to generate elevation data at a 9.86-m resolution. The nominal orbital characteristics and geometry of the SPOT (Système Probatoire D'Observation de la Terre) satellite were convoluted with the data files to produce simulated panchromatic High Resolution Visible (HRV) digital stereo imagery for three different orbital paths. Techniques were developed for reconstructing topographic data. Essentially, these techniques coalign a nadir and off-nadir pass to calculate the stereo displacement for each pixel in the nadir view by correlating a small subarea to a corresponding subarea in the off-nadir pass. Preliminary analyses with the simulated HRV data and two pairs of data sets consisting of patterns of bars and boxes verify the efficacy of this technique.