Q: What format should my DEM be in when using aplcorr?

A:
APL expects the Digital Elevation Model (DEM) to be in a 1-band ENVI BIL or BSQ file format. This is a simple binary format where the data is stored as a string of binary information with an accompanying header file that describes the number of bands / lines / samples. Further information on this file format can be found in the ENVI tutorial: ​http://www.exelisvis.com/portals/0/tutorials/envi/ENVI_Intro.pdf

The elevation data should be projected in WGS84 Latitude and Longitude with heights referenced to the WGS84 spheroid.