Investigation of the Dependence of Lidar Echo Signal Characteristics on the Length of the Sounding Path

Field measurements of the characteristics of the bottom-reflected lidar echo signal were conducted in the waters of Bechevinskaya Bay. The studies employed the APL‑3 airborne polarization lidar (sounding pulse energy of 45 mJ, receiving optical system diameter of 100 mm, and system response function duration at the 0.5 level of 10.8 ns). The depth range during the investigations varied from 3 to 22 m, while the flight altitude ranged from 500 to 1200 m. The hydrooptical characteristics of the bay waters were assessed based on lidar sounding data. For the analysis of field measurement data, areas with similar values of the lidar attenuation coefficient were selected. The results of field experiments demonstrated that the relationship between the magnitude of the lidar echo signal and the length of the sounding path for water layers and the seabed is more complex than what is suggested by the conventional form of the lidar equation. The introduction of an additional term into the lidar equation, which defines the dispersion of the irradiance distribution in the cross-section of an infinitely narrow beam of light passing through a water layer of a given thickness, allowed for a more accurate description of the obtained experimental dependencies. The registered effect must be taken into account when designing lidar systems, as well as during the processing and analysis of lidar survey data.