Opposition Effect from Clementine Data and Mechanisms of Backscatter

Abstract

An analysis of Clementine data obtained from a UVVIS camera and simulating laboratory photometric and polarimetric measurements is presented with the use of a new photometric threeparameter function combining the shadow-hiding and coherent backscatter mechanisms. The fit of calculated curves to the average brightness phase function of the Moon derived from Clementine data indicates that the coherent backscatter component is nonzero. The average amplitude of the opposition surge of the Moon in the range of phase angles 0• -1• is approximately 10%. The Clementine data also show a flattening of phase-dependent brightness at angles less than 0.25• that is caused by the angular size of the solar disk. The lunar brightness phase curves at small phase angles are nearly the same in different wavelengths even though at larger phase angles (5• -50 • ) the lunar surface becomes distinctly redder with increasing phase angle. According to the model, the lack of wavelength-dependent brightness variations at small phase angles can be due to quasifractal properties of the lunar surface. Results of related laboratory measurements suggest that: (1) besides the narrow coherent backscatter opposition spike there is a broad component which can contribute to phase angles up to 10• and (2) a component of coherent backscatter can be important even for low albedo surfaces. The latter testifies the opposition effect of the lunar surface to be substantially formed by the coherent backscatter mechanism.

Atmospheric aerosol limb scanning based on the lunar eclipses photometry

“…But we will compare the brightness of the region on the Moon during the eclipse only with the one in the same region out of eclipse at the fixed angular distance from the umbra center (1.6° was chosen). However, the phase angle during the eclipse can differ about 0.5° -1° from such conditions that can lead to brightness change [5], but almost constant value of lunar brightness outside penumbra (it changes on less than 2% per 1 degree of distance from umbra center) after the eclipse of May, 4, 2004, shows the insufficiency of this effect for our work.…”

The wavelength dependence of the lunar phase curve as seen by the Lunar Reconnaissance Orbiter wide‐angle camera

“…[49] Moreover, a large number of laboratory studies of planetary regolith analog powders composed of particles larger than the wavelength in contact with each other found no wavelength dependence [Shkuratov et al, 1999;Nelson et al, 2002;Kaasalainen et al, 2005]. Also, equation (17) shows that L Τ is a strong function of particle size and spacing, yet none of these laboratory analog samples displayed the dependence predicted by equations (10) and (17) [Nelson et al, , 2000Shkuratov et al, 1997;Kaasalainen, 2003;Piatek et al, 2004].…”

“…Since present theories of the CBOE predict that it should vary strongly with wavelength, these workers concluded that the lunar OE was due mostly or completely to SHOE. However, it is important to verify these results by independent observations, particularly since questions remain concerning the calibration of the Clementine cameras [Shkuratov et al, 1999Hillier et al, 1999].…”

“…The first spacecraft measurements of the wavelength dependence of the lunar OE were acquired with the Clementine ultraviolet-visible (UVVIS) imaging system [Buratti et al, 1996;Hillier et al, 1999;Shkuratov et al, 1999]. More recent observations have been made by the Chandrayaan spacecraft [e.g., Hicks et al, 2011].…”

Asteroid Photometry

“…Therefore it is nearly impossible to find exact, unique solutions of radiative transfer equations that describe real asteroidal surfaces. Some assumptions and approximations have to be made in order to derive practical analytical models, such as the Hapke model (Hapke, 1981;1986;2002;2008;2012a), the Shkuratov model (Shkuratov et al, 1999), etc. Observationally, due to the limited observing geometries available for ground-based and spacecraft observations to any asteroid, it is often difficult to fully constrain a photometric model for a particular object.…”