This tool calculates a normal map from a raw 16 bit unsigned short little endian height map and outputs the generated normal map into a raw 16 bit unsigned short little endian image file. Developed against the OS X 10.8 SDK, link this against the Accelerate framework.
See http://poniesandlight.co.uk/notes/creating_normal_maps_from_nasa_depth_data/ for a full write-up, and for some super high-rez normal maps of earth.