A Study to Measure Optical Properties of Waters by Oceanographic Lidar with variable Field-of-View

摘要

Return signal of oceanographic Lidar is a decaying exponential function of the attenuation coefficient which is related to the optical properties of water. The Lidar attenuation coefficient ( K_(lidar)) obtained from traditional oceanographic Lidar with single field of view (FOV) cannot be used to effectively estimate parameters of the water optical properties due to the deficiency of Lidar equation. However, this exponential decay of elastic backscattering from water is strongly dependent on both FOV of Lidar and optical properties of water. Thus, an approach using a variable FOV receiver has become a potential way to compensate the deficiency in the measurement by traditional Lidar. Three major parts are presented in the paper. Firstly, on the basis of historical models of oceanographic Lidar, a practical model between K_(lidar) and FOV angles is derived to estimate the optical property parameters, namely a (absorption coefficient), b (scattering coefficient) and K_d (diffuse attenuation coefficient). Secondly, for the purpose of getting the appropriate FOVs of a shipboard oceanographic Lidar, return signals are simulated under different FOVs to analyze the relationship between K_(lidar) and the water optical parameters with the impact of background noise taken into account. Finally, the experiments are conducted to measure optical properties of water by using oceanographic Lidar with different FOVs. The optical properties of water bodies are estimated in the cases of different FOVs, and the accuracy of measurements is analyzed. Experimental analysis verifies the feasibility of measuring multiple optical properties of seawater by oceanographic Lidar with variable FOV.