Here is my attempt at creating a Topographic Exposure Index. Topographic exposure or TOPEX essentially looks out from a given pixel and scans the surrounding landscape for maximum angles from the given pixel on a digital elevation model. Maximum angles are measured for each of 8 horizontal direction classes and those maximums are summed for the final score. A high TOPEX value would indicate a very sheltered area whereas a value of 0 would indicate you were on a flat plain or mountain top.
I ran it on the Blue River Watershed in Oregon and it took it about 5 days to complete. The input DEM was 7084x5882 pixels and the search kernel looked out 2,500m. The main innovation relative to other implementations I have seen is I created a kernel with concentric rings to scan the landscape for maximum ridge angles within 8 horizontal direction classes. The example below has 50 concentric rings which are separated by 50m. The DEM was at a 5m resolution so I went with a relatively fine spacing for the concentric rings.
