Wind speed dependence of atmospheric boundary layer optical properties and ocean surface reflectance as observed by airborne backscatter lidar

Abstract

Airborne backscatter lidar measurements made over the Azores, in clear air conditions, are analyzed using a marine aerosol model to derive the extinction coefficient in the atmospheric boundary layer and the ocean surface reflectance in connection with surface wind speed. The dependence of surface layer extinction coefficients on surface wind speed is compared to previously published results. The sensitivity of the lidar inversion procedure to the aerosol model (sea‐salt concentration in the accumulation mode, presence or absence of an accumulation mode for sulfate, vertical distribution of stationary marine components above the marine atmospheric boundary layer) is investigated. At the wavelength of the lidar (0.53 μm), the extinction coefficient is very sensitive to the sea‐salt number concentration in the accumulation mode. In the surface layer, the extinction coefficient retrieved from the lidar measurements compares well to the extinction calculated with the model (via Mie theory) for an average number concentration of 10 particles cm⁻³ in the sea‐salt mode at wind speeds less than 3 m s⁻¹. The relationship between the sea surface reflectance and the atmospheric backscatter coefficient is then used to determine the optical sea surface properties as a function of wind speed. Results on reflectance are found in excellent agreement with calculated values using the model of Cox and Munk [1954] and measured wind speed. The sensitivity of the results to the aerosol model and potential application of the inversion procedure to surface wind speed retrievals from lidar measurements are also discussed.