In the reference given in the ENVI docs, the algorithm shows "log", with no explanation.  I believe that this means log base 10, or else they would have used a different notation, or would have given some kind of note about the base of the log.  My understanding from reading the reference (see below) is that the SID values naturally fall between 0 and 1.  At any rate, all of the values discussed in the reference fall in that range.  I don't think there is any scaling involved.  I am looking at equations 7, 8 and 9 in the reference: Du, H., C.-I. Chang, H. Ren, F.M. D'Amico, J. O. Jensen, J., "New Hyperspectral Discrimination Measure for Spectral Characterization," Optical Engineering, Vol. 43, No. 8, 2004, 1777-1786. Peg