Topic: KH9 Hexagon satellite images
KH9 Hexagon satellite images are essentially very very high altitude aerial photos, since they are acquired with a frame camera system.
Here's how to get started orthorectifying them. I've correlated them with SPOT5 satellite imagery (aqcuired with the completely different pushbroom system) and had great success! Processing Hexagon images is not difficult, but certainly more time consuming than Landsat, ASTER and SPOT. Here's a quick summary:
1. You can buy your Hexagon images from the USGS for $30 a pop.
2. When they arrive, you need to stitch the two halves of the Hexagon image together. You will notice there are crosses (reseau points) on the Hexagon images... there are 23 in the x-direction and 47 in the y-direction. If the very center reseau point has a coordinate of (0,0), and x increases to the right, and y increases up the image, then the reseau point with the coordinate (23,23) should have a little flag on it. This should be visible on both halves of the raw Hexagon image, and which you can use to mosaic the two images together using the Mosaicing > Pixel-based tool in ENVI. Once your two image halves are adequately mosaiced together, rotate the image so North is at the top. (* it is best if the feature of interest is far away from the stitching line i.e. in the middle of either of the two halves is ideal).
3. To generate the interior orientation info, I use the reseau-based coordinate system described above. The distance between each reseau point is 1 cm, and so the Upper Left fiducial would be x = -110 mm y = 230 mm, Upper Right: x = 110 mm, y = 230 mm, Lower Right: x = 110 mm, y = -230 mm, Lower Left: x = -110 mm, y = -230 mm. For the focal length, use 30.5 cm. Don't worry about optical distortions for the moment, since we don't actually know what they are. If the magnitude of displacements you are measuring is greater than 10 m then the errors introduced by optical and film distortions will be relatively small. Otherwise, I've managed to image 4 m fault displacements, but this only works because the signal is high-frequency. Distributed deformation of 10 m or less will be very difficult to see above the noise.
4. The rest of the procedure is relatively painless... you use the aerial photo module in Cosi-Corr, and process the hexagon image as if it were an aerial photo. I usually orthorectify them at 7 m resolution.