Calibration method for the lidar-observed stratospheric depolarization ratio in the presence of liquid aerosol particles

A fine calibration of the depolarization ratio is required for a detailed interpretation of lidar-observed polar stratospheric clouds. We propose a procedure for analyzing data by using atmospheric depolarization lidar. The method is based on a plot of delta (T) versus (1-R-T(-1)), where delta (T) is the total depolarization ratio and R-T is the total backscattering ratio. Assuming that there are only spherical particles in some altitude ranges of the lidar data, the characteristics of the plot of delta (T) versus (1-R-T(-1)) lead to a simple but effective calibration method for delta (T). Additionally, the depolarization of air molecules delta (m) can be determined in the process of delta (T) calibration. We compared determined values with theoretically calculated values for the depolarization of air to test the proposed method. The delta (m) value was calculated from the lidar data acquired at Ny-Alesund (79 degreesN, 12 degreesE), Svalbard in winter 1994-1995. When only sulfate aerosols were present on 24 December 1994, delta (m) was 0.46 +/- 0.35%. When the particles consisted of sulfate aerosols and spherical particles of polar stratospheric clouds on 4 January 1995, delta (m) was 0.45 +/- 0.07%. Both delta (m) values were in good agreement with the theoretically calculated value, 0.50 +/- 0.03%. (C) 2001 Optical Society of America.