Effects of atmospheric moisture on the radiation intensity of objects in millimeter-wave band

Abstract

The complex weather system in Taiwan often brings precipitation that decreases the accuracy of electromagnetic-wave guided weapons. In order to solve this problem, this paper aims at assisting the weapons to distinguish the difference between targets and background environment at a relatively accurate level. Given the characteristics of thermal radiation (brightness temperature), which is a type of electromagnetic-wave, are able to distinguish the differences between target areas and background atmosphere, the thermal radiation has been detected by using a dual-polarization radiometer in the millimeter-wave band (36.5 GHz) during the period of 98 days from 3rd May to 8th August in 2014.Two remarkable results are found to assist us to improve the accuracy of the weapons. First, the difference of brightness temperatures between the background atmosphere and the targets including tanks, grass and a forest is 100 K. Second, a difference of 15 K caused by diurnal changing is also identified. It is not surprising for us to learn that the brightness temperatures of the targets are gradually approaching to be comparable with the background when the rainfall is increasing. Identifying the targets by the weapons becomes much more difficult given the difference of the brightness temperatures between the targets and the background becomes minor. We also identify that the quantities of rain rate constrain the function of the radiometer. When the rain rate is lower than 20 mm per hour, the radiometer is capable to accurately detect the difference between the targets and the background. However, the higher the rain rate, the lower the accuracy of the radiometer. The radiometer is totally disable to detect any difference when the rain rate is above 58.2 mm per hour.