Key points are not available for this paper at this time.
Gale W. Croon, Dale R. McCullough, Charles E. Olson, Jr., Leland M. Queal, Infrared Scanning Techniques for Big Game Censusing, The Journal of Wildlife Management, Vol. 32, No. 4 (Oct., 1968), pp. 751-759
Croon et al. (1968) studied this question.