Personal camouflage. Surface temperature and its dependence on climate, physical activity and material properties. Computer simulations and climatic chamber studies on combat uniform 90 and two camouflage suits

This study deals with the thermal camouflage properties of a combat uniform (FU90) and two camouflage suits, FRYNSER och ULCAS (SAAB Barracuda AB). The study was run in a combined climatic chamber and wind tunnel. The climate was 10,3°C, 58% rh and 19,7°C, 63% rh. Air speed was 0 m/s and 2 m/s. A few measurements were also done at 5 m/s. Solar radiation lamps (800 W/m2) were also used. The physical activity was standing still and walking on a treadmill at 1,5 m/s and the slope 1,4°. Surface temperature was measured with an IR-camera. The results showed that the camouflage effect is improved if the suit is made thicker (higher insulation value) and the effect is further improved at wind. The effect of wind is greater than that of body movements. Surface temperature of FRYNSER (thickest) exceeded air temperature (at 20°C) with roughly one degree at wind. The surface temperature of FU90 was, without solar radiation, a few degrees higher than FRYN SER at 20°C and about 5 degrees at 10°C. Solar radiation and calm air make the effect of a camouflage suit limited. In case of sun, wind improves the effect of camouflage. The difference between a thick camouflage suit and a combat uniform can be about 10°C at sun and an air temperature of 20°C. Yet, the camouflage can be lost at stronger winds if the suit material starts to flap. Measurements were compared with temperature estimations obtained from a simulation program (INSULA). The correlation between the two methods was very god. The results suggest that using low-emissivity materials may give some advantages. The study emphasises the importance of camouflage for the face and nude hands. In many situations the advantage of a camouflage suit may become negligible if the thermal signature is not reduced significantly.