Polarization Changes in Lunar Simulant Soil: The Role of Incident, Reflection, and Off-Plane Angles

Abstract

Observing the polarization of the lunar regolith is essential for obtaining detailed information about the composition and characteristics of lunar soil. Observations conducted via lunar orbiters facilitate polarization measurements over wide areas; however, achieving very high-resolution imaging requires either a large optical system or a narrow field of view, both of which complicate observations under varying incident angle conditions. Furthermore, when the lunar surface is imaged at high resolution, the emission angle can vary significantly due to the slope and orientation of local terrain features such as craters and hills. This variability is particularly pronounced in young craters, where steep slopes near the rim result in emission angles that are nearly horizontal. In addition, unlike ground-based observations, orbital systems can observe the same region at various times and from different angles, resulting in significant variation in the off-plane angle between the satellite, the target area, and the Sun. Consequently, the Sun, target, and detector may not align linearly on the lunar surface. In this study, we measured the degree of polarization of the JSC-1A lunar soil simulant at various incident, reflection, and off-plane angles to examine how the polarizer angle changes under different conditions. The results show that even at the same phase angle, the degree of polarization varies significantly with incident and off-plane angles, indicating that these geometric factors must be considered for accurate interpretation of polarization measurements. These measurements are expected to aid in identifying critical factors for accurately interpreting polarization data obtained from the lunar surface.