The Lunar Opposition Surge: Observations by Clementine

Abstract

The Clementine mission to the Moon in 1994 provided the first multispectral observations of the lunar opposition surge below a few degrees. The brightness of the Moon increases more than 40% between solar phase angles of 4° and 0°. The opposition effect exhibits a small wavelength dependence: the surge is ∼3–4% larger at 0.41 μm than at 1.00 μm. This result suggests that the principal cause of the lunar opposition surge is shadow hiding, while coherent backscatter, if present, makes only a minor contribution. The amplitude of the effect depends significantly on terrain: the surge is about 10% greater in the lunar highlands. This difference is attributed to textural variations between the two terrains. The Clementine measurements provide a new basis for deriving spectral geometric albedos, phase integrals, and Bond albedos. A value of 0.11 ± 0.01 was found for the lunar bolometric Bond albedo. This value is at the low end of the historical published values, but not as low as the recent result of 0.080 ± 0.002.