Airborne measurements of laser backscatter from the ocean surface

Abstract

Laser backscatter data for the ocean surface near nadir have been acquired from an airborne lidar platform. The unique capability of this lidar instrument to scan both transmitted laser beam and receiver field of view up to 15° off nadir have made these data sets possible. Backscatter data were collected on eight separate missions using laser wavelengths at 337 and 532 nm and 9.5 μm. Statistics of the mean, standard deviation, and probability density function of backscatter were computed and analyzed in terms of prior analytical work that relates backscatter to wind speed and mean-square wave-slope statistics. We found the full width at half-maximum of the Gaussian-shaped mean backscatter pattern to range from 11 to 24° and the normalized standard deviation at a nadir-viewing angle to range from 0.1 to 0.6. We calibrated mean backscatter at nadir for the ocean surface in terms of an effective Lambertian reflectance by comparison of beach sand and ocean backscatter. Results were 16 and 24% reflectance on two missions where calibration was possible. Our data are compared with prior laser backscatter measurements and the general literature on optical scattering from the ocean surface.