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].sub.T] versus (1 - [R.sub.T.sup.-1]), where [[delta].sub.T] is the total depolarization ratio and [R.sub.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].sub.T] versus (1 - [R.sub.T.sup.-1]) lead to a simple but effective calibration method for [[delta].sub.T]. Additionally, the depolarization of air molecules [[delta].sub.m] can be determined in the process of [[delta].sub.T] calibration. We compared determined values with theoretically calculated values for the depolarization of air to test the proposed method. The [[delta].sub.m] value was calculated from the lidar data acquired at Ny-[Angstrom]lesund (79 [degrees] N, 12 [degrees] E), Svalbard in winter 1994--1995. When only sulfate aerosols were present on 4 December 1994, [[delta].sub.m] was 0.46 [+ or -] 0.35%. When the particles consisted of sulfate aerosols and spherical particles of polar stratospheric clouds on 4 January 1995, [[delta].sub.m] was 0.45 [+ or -] 0.07%. Both [[delta].sub.m] values were in good agreement with the theoretically calculated value, 0.50 [+ or -] 0.03%. OCIS codes: 010.1100, 010.1310, 010.3640.