Performs Spectral Angle Mapping on a set of spectra. Each spectrum is treated as a vector in band-space (where each spectral band is considered a basis), and the angle between the input and reference spectra is calculated to determine similarity. Emits an array of angles, one for each reference spectrum provided.

For more information see:

Kruse, Fred A, Lefkoff, AB, Boardman, JW, Heidebrecht, KB, Shapiro, AT, Barloon, PJ, Goetz, AFH (1993). The spectral image processing system (SIPS)