Estimation of Atmospheric Optical Parameters with Simultaneous Measurement of Vibrational-Rotational and Purely Rotational Raman Spectra

Abstract

The paper considers the methodological features of determining the optical extinction and backscattering coefficients by simultaneous lidar measurements at the following wavelengths: 532 nm (elastic scattering, ES), 607 nm (vibrational-rotational Raman scattering, RS), and 530 nm (purely rotational RS). The ES signal identifies the range of allowable values (RAV) of the coefficients based on the a priori introduction of a physically substantiated lidar ratio. The RS signal at λ = 607 nm, corresponding to a single line of the N₂ spectrum, provides a plausible estimate of the ratios in the boundary layer and part of the middle troposphere. The RS signal at vλ = 530 nm—a set of N₂ and O₂ spectrum lines—is characterized by smaller errors and provides a quantitative estimate of the coefficients in all main tropospheric layers. At a wavelength of 530 nm, the differential backscattering cross section depends on height due to temperature changes, which leads to a redistribution of N₂ and O₂ line intensities. Estimation of parameters from the RS signals is considered plausible when the sought-after coefficients are quantitatively comparable and located within their RAVs. Testing of the algorithms is carried out using ground-based sensing data on the shore of Lake Baikal in August 2023.