Laser propagation transmission properties characteristics between airborne communication terminal and unmanned aerial vehicle target in complex atmospheric background

Abstract

Clouds, aerosols and atmospheric molecules are major components of the atmosphere. In the fields of atmospheric physics such as target detection, wireless optical communication and remote sensing, these atmospheric components have a strong attenuation effect on laser transmission. Based on the successive scattering method for solving the radiative transfer equation, the laser transmission model between airborne wireless optical communication terminal and ground-to-air unmanned aerial vehicle (UAV) target in complex atmospheric background is established in this paper. Considering the fact that cirrus cloud, atmospheric molecules and aerosols exist in the real atmospheric background, the variations of direct transmission power, first-order scattering transmission power of 1.55 μm laser emitted by the airborne wireless optical communication terminal with UAV target height are calculated numerically under complex atmospheric background. The effects of the aircraft located at different locations, effective radius of ice crystal particles in cirrus cloud, as well as the horizontal distance between the aircraft and UAV target on received laser transmission power are also analyzed. In the first three examples (i.e., aircraft is above, below, and inside cirrus cloud), laser direct transmission power (LDTP) is much larger than first-order scattering transmission power (FSTP); when the UAV target rises into the cloud, the FSTP is significantly enhanced as a result of the effect of diffraction light. The fourth example is for calculating the variations of LDTP and FSTP with UAV target height for different effective radii of ice crystals. The results show that the LDTP decreases with the increase of effective radius, whereas the FSTP presents an opposite scenario. The fifth example is for calculating the variations of LDTP and FSTP with UAV target height for different horizontal distances. The results show that the LDTP and FSTP decrease with the increase of the horizontal distance, which is obviously realistic. In summary, it is concluded that the laser transmitted power through cirrus clouds is strongly dependent on aircraft position: above, below, or inside cirrus cloud; the horizontal distance between the aircraft and UVA target, and effective radii of ice crystals have great influences on LDTP and FSTP. Compared with the atmosphere above the clouds, the molecules and aerosols below the clouds make the laser power have a strong attenuation. The results given in this paper provide theoretical support for further studying the laser communication experiment in ground-to-air links, UAV formation, command and networking technology in complex atmospheric background.