Measurements at SRDE have shown that objects in nature emit radiation above about 2 microns. For instance it has been shown that a black body at a temperature of 27 degrees Centigrade emits energy that rises steeply to a maximum at 10 microns with a magnitude five orders more than at 1.6 microns and seven orders more than that of visible starlight. An infra-red device detecting these wavelengths was used as a target detector to aid the passive image intensifiers operating in the near infra-red to produce an image of the target.