Determination of the cirrus particle single-scattering phase function from lidar and solar radiometric data

Abstract

The single-scattering phase function of cirrus particles in the free atmosphere has been determined between angles of 15 and 90° in the forward direction and at 180° in the back direction. The technique involved measuring the solar radiation intensity scattered by thin cirrus with a lidar receiver and also determining the cirrus optical depth simultaneously from a lidar backscatter return. The solar scattered radiance appeared as a background signal on the lidar echo. The phase function at 180° was determined from the integrated cloud backscatter using standard techniques. Data were obtained during two experimental phases covering summer and winter periods. The values of the measured scattering functions fell within the range of various laboratory measurements. The results showed evidence for the 22° halo associated with scattering from hexagonal crystals.