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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 clouds 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. [ABSTRACT FROM AUTHOR]

In order to understand the regolith characteristics of the Reiner Gamma swirl, one of the most prominent lunar swirls, we analyze the correlation between the linear polarization fluxQand the intensity I of the swirl. We present comparisons between the phase function (the intensity variation with the phase angle) of the swirl and the phase functions of its neighbors using polarimetric data. We find that the swirl has unusually large Q values for given I values. We also show that the phase function of the swirl is relatively shallow compared to its neighbors. We suggest that the microstructure of the regolith on the Reiner Gamma swirl has been disrupted. [ABSTRACT FROM AUTHOR]

PolCam, a wide-angle polarimetric camera, will be onboard the Korea Pathfinder Lunar Orbiter to investigate the lunar surface based on polarimetry. PolCam will construct a global lunar map of polarimetric parameters, such as maximal polarization (Pmax) and titanium distribution using three color bands centered at 320, 430, and 750 nm. PolCam's twin cameras are mounted at 45° tilt angles from the nadir across the orbital track in opposite directions. PolCam will obtain polarimetric measurements of sunlight scattered by the lunar surface at various phase angles up to ∼140° to achieve the scientific goals during the one-year mission. Since degree of linear polarization is a function of phase angle, it is essential to perform several measurements at various phase angles to properly retrieve, e.g., Pmax, Pmin, and the inversion angle, αinv. In this work, we show PolCam's phase-angle coverage as a function of selenographic longitudes from the equator to latitudes up to 70°N. Decreasing tilt angle to 25° and 0° limits the high end of phase-angle coverage, as well as the observational chances at high latitudes. [ABSTRACT FROM AUTHOR]

Polarimetry of the Moon reveals characteristics of the lunar regolith such as the size and composition of regolith grains, which are useful in understanding the surface properties and to determine landing sites for future lunar missions. As part of the Korea Pathfinder Lunar Orbiter (KPLO) mission, the wide-angle polarimetric camera (PolCam) will perform polarimetric measurements of the Moon for the first time from the lunar orbit. Because the degree of linear polarization is a function of the phase angle, it is necessary to observe the same region multiple times at various phase angles to construct the phase curve of polarization and derive the map of maximum polarization (Pmax). Any unexpected discontinuities of observing runs or an abrupt termination of the mission may cause the scientific goals of the PolCam to be unachievable. Here, we investigated how to recover the polarimetric phase curve when the observational data set is incomplete. Using ground-based polarimetry data, we explored the parameter space of the fitting formula of the phase curve and show that the formula can be reduced into a single parameter form. Assuming several cases of incomplete measurements, we constructed Pmax maps and investigated the allowable range of the phase-angle coverage. We show that Pmax can be estimated with a root-mean-square discrepancy less than 0.5%p when the maximum phase angle covered is greater than 90°. [ABSTRACT FROM AUTHOR]

To understand grain size evolution on the lunar surface in detail, we analyze the distribution of the average grain size for the lunar near side obtained by Jeong et al. Furthermore, we analyze the polarimetric properties of the regolith simulants SiC and JSC-1A in a laboratory. We find two characteristics of grain size evolution on the Moon. First, the lunar regolith has evolved on a specific evolutionary pathway in space. Here, Φ is defined as the ratio of the perpendicular () and parallel () components of the reflectance. Second, we also find that the evolutionary pathway depends on the FeO abundance and selenographic latitude of the surface. The dependence on the FeO content seems to result from the different resistance to comminution of regolith materials, and the dependence on the latitude seems to result from differences in the resurfacing environment. We present the probable causes of these characteristics of grain size evolution on the lunar surface. [ABSTRACT FROM AUTHOR]