The influence of secondary Rayleigh scattering on the characteristics of a passive lidar for the detection of laser radiation in the atmosphere
The paper solved the problem of determining the received scattered optical power from weakly diverging laser beams propagating in the Earth’s atmosphere with a passive laser locator (lidar) in a weakly turbid atmosphere taking Rayleigh secondary scattering into account and was determined the lidar action radius for these conditions. At night conditions without solar illumination, the lidar range can be more than 4500 km when detecting beams with a power of about 100 kW in the wavelength range of ~ 1600 nm. In the presence of solar illumination, the range of the lidar is reduced by an order of magnitude. The dependences of the detection radius and the power received by the lidar for the wavelengths of external radiation in the ranges of 1650 nm, 1000 nm, and 500 nm are also calculated. Despite the fact that scattering is inversely proportional to the fourth power of the light wavelength, at large distances the radius of action of the lidar decreases with a decrease in the wavelength of third-party radiation due to significantly large losses from secondary Rayleigh scattering. The dynamic range of the detection radius at a wavelength of 500 nm is from ~ 20 km when locating beams with a power of ~ 10 W to ~ 200 km when locating high-power beams ~ 100 000 W, which is less than at other wavelengths. However, smoke particles (aerosols) are always present in the real atmosphere, and almost always, besides molecular, there is also aerosol scattering, which can limit the detection range considered in this model. Experimental and theoretical data are consistent with each other in the region of a small magnitude of the detection range and the power of an external beam, which confirms the correctness of the theoretical approach to the problem being solved and allows extrapolating the results to high beam powers.