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Technical note: A simple method for retrieval of dust aerosol optical depth...

Sun, W., Y. Hu, R. R. Baize, G. Videen, S. S. Kim, Y. Choi, K. Kang, C. K. Sim, M. Jeong, A. H. Omar, S. Stamnes, D. G. MacDonnell, and E. Zubko (2019), Technical note: A simple method for retrieval of dust aerosol optical depth with polarized reflectance over oceans, Atmos. Chem. Phys., 19, 15583-15586, doi:10.5194/acp-19-15583-2019.
Abstract: 

Our previous study shows that the angle of linear polarization (AOLP) of solar radiation that is scattered from clouds at near-backscatter angles can be used to detect super-thin cirrus clouds over oceans. Such clouds are too thin to be sensed using any current passive satellite instruments that only measure light’s total intensity, because of the uncertainty in surface reflection. In this report, we show that with a method similar to the super-thin cloud detection algorithm, dust aerosols may also be detected and differentiated from clouds. We also show that the degree of polarization of reflected light can be used for retrieving the optical depth of dust aerosols in the neighborhood of the backscatter angle, regardless of the reflecting surface conditions. This is a simple and robust algorithm, which could be used to survey dust aerosols over midlatitude and tropical oceans.

A NASA-Korea CubeSat mission is currently under preparation by NASA Langley Research Center, the Korea Astronomy and Space Science Institute (KASI), and Kyung Hee University of Korea. We plan to use polarimeters on two CubeSats to detect the super-thin clouds over global oceans and dust aerosols over oceans and land around the Korean Peninsula. The polarimeters will be developed by KASI and are modified versions of the Polarimetric Camera (PolCam) developed by KASI for the Korea Pathfinder Lunar Orbiter (KPLO). This planned polarimeter-on-CubeSat mission will measure the polarization features of scattered light from clouds and aerosols to identify the super-thin clouds and dust aerosols over oceans and retrieve their optical depth.

Our previous works (Sun et al., 2014, 2015) show that distinct features exist in the angle of linear polarization (AOLP) of solar radiation that is scattered from clouds at nearbackscatter angles. At these angles the dominant electric field from clear-sky oceans is nearly parallel to the Earth’s surface. However, when clouds are present, this electric field can rotate significantly away from the parallel direction. Our modeling results suggest that this polarization feature can be used to detect super-thin cirrus clouds with an optical depth of only ∼ 0.06 and super-thin liquid water clouds with an optical depth of only ∼ 0.01. Such clouds are too thin to be sensed using any current passive satellite instruments that

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Research Program: 
Radiation Science Program (RSP)
Mission: 
NASA Langley Research Center’s “Lidar Data Analysis and Theory” project