|Paper title||Daytime Polarization Calibration Using Solar Background Signal Scattered from Dense Cirrus Clouds in the Visible and Ultraviolet Wavelength Regime|
|Form of presentation||Poster|
Daytime Polarization Calibration Using Solar Background Signal Scattered from Dense Cirrus Clouds in the Visible and Ultraviolet Wavelength Regime
Zhaoyan Liu, Pengwang Zhai, Shan Zeng, Mark Vaughan, Sharon Rodier, Xiaomei Lu, Yongxiang Hu, Charles Trepte, and David Winker
In this presentation we describe the application of a previously developed technique that is now being used to correct the daytime polarization calibration of the CALIPSO lidar . The technique leverages the fact that the CALIOP solar radiation background signals measured above dense cirrus clouds are largely unpolarized  due to the internal multiple reflections within the non-spherical ice particles and the multiple scattering that occurs among these particles. Therefore, the ratio of polarization components of the cirrus background signals provides a good estimate for the polarization gain ratio (PGR) of the lidar. Using airborne backscatter lidar measurements, this technique was demonstrated to work well in the infrared regime where the contribution from the molecular scattering between dense clouds is negligible. However, in the visible and ultraviolet regime, the molecular contribution is too large to be ignored, and thus corrections must be applied to account for the highly polarizing characteristics of the molecular scattering. Ignoring these molecular scattering contributions can cause PGR errors of 2-3% at 532 nm, where the CALIPSO lidar makes its depolarization measurement. Because of the wavelength dependence of -4 of the molecular scattering, the PGR error can be even larger at the 355 nm wavelength that will be used by ESA’s EarthCARE lidar. To estimate the molecular scattering contributions to the lidar received solar background signal, a look-up table has been created using a polarization-sensitive radiative transfer model . This presentation describes the theory and implementation of the molecular scattering correction, demonstrates the application of the calibration technique, and compares the results to CALIOP daytime PGR estimates derived using an onboard pseudo-depolarizer . We also present the simulation results at 355 nm at the symposium.
1. Z. Liu, M. McGill, Y. Hu, C. Hostetler, M. Vaughan, and D. Winker, “Validating lidar depolarization calibration using solar radiation scattered by ice clouds”, IEEE Geos. and Remote Sensing Lett., 1, 157-161, 2004.
2. K. N. Liou, Y. Takano, and P. Yang et al., “Light scattering and radiative transfer in ice crystal clouds: applications to climate research,” in Light Scattering by Nonspherical Particles, M. Mishchenko et al., Eds. San Diego, CA: Academic, 2000, pp. 417–449.
3. P. Zhai, Y. Hu, J. Chowdhary, C. R. Trepte, P. L. Lucker, D. B. Josset, “A vector radiative transfer model for coupled atmosphere and ocean systems with a rough interface”, Journal of Quantitative Spectroscopy and Radiative Transfer, 111, 1025-1040, 2010.
4. J. P. McGuire and R. A. Chapman, “Analysis of spatial pseudo depolarizers in imaging systems,” Opt. Eng., vol. 29, pp. 1478–1484, 1990.