A NASA report by R. Kumar, dated Sep 1, 1977, available online and downloadable as a PDF document.

ABSTRACT:

The effects of temperature and emittance on the relative magnitude of reflected energy and emitter energy from a target including atmospheric effects was studied. From the calculations of energy reflected and emitted from a target including atmospheric effects using LOWTRAN 3 programs for midlatitude summer model, the following conclusions were obtained (1) At 3.5 micrometers q is considerably less than 1 except at high temperatures and for high emittance (2) at 4 micrometers q is of the order of magnitude equal to 1 for most targets and (3) at 4.6 micrometers, q is considerably greater than 1 at high temperatures and high emittance. In addition, incident atmospheric emission reflected from the target was found to be negligible except for targets having low temperature and low emittance.