The detectability of a target in the infrared spectral region is determined by differences between the radiative signatures of the target and the local background. This implies that both, the difference in surface temperature and emissivity (Delta) T resp. (Delta) (epsilon) and the distribution of these differences over the target area and the background, are of major importance. Therefore camouflage measures have to address both issues in order to achieve maximum signature adaptation to the background. To determine the ability of a camouflage material to follow temperature changes in the background, temperatures measurements of camouflage systems and background elements have to be performed under a variety of meteorological conditions. Measurements of representative weather- and background conditions are needed to determine those situations where the camouflage material effectively reduces the target signature. The degree of temperature reduction depends on the required level of protection, that is for detection, recognition, and identification. Statistical analyses are given for various camouflage materials in relation to a number of background elements. Camouflage effectiveness is expressed in the percentage of time for which the apparent temperature contrast between the camouflage material and a background element is 1 degree(s)C, 2 degree(s)C, or 5 degree(s)C. Analyses are performed for five consecutive weeks of measurements in summer and winter, using data which were taken during a measurement campaign at Gilze-Rijen Air Force Base in 1990.