Determination of the sub-terahertz attenuation of brownout clouds generated by rotorcraft

The development of imaging systems operating in brownout (BO) conditions is a growing field of research as it is a cause of numerous fatal accidents. Devices based on sub-THz waves have been proposed to equip helicopters operating such degraded visual environment. However, the attenuation due to the presence of a brownout cloud and absorbing atmosphere remain challenging to determine accurately. We propose in this study to perform an experimental determination of the attenuation of different brownout clouds from 0.1 to 1.0 THz. Based on these field measurements in controlled brownout environment at ONERA facilities, an empirical model is proposed to compute the attenuation due to the brownout cloud with and without absorbing atmosphere. Lastly, we have demonstrated that scattering of sub-THz by sand particles cannot be neglected.