Occurrence probability of slopes on the lunar surface: Estimate by the shaded area percentage in the LROC NAC images

Abstract

The paper describes the method of estimating the distribution of slopes by the portion of shaded areas measured in the images acquired at different Sun elevations. The measurements were performed for the benefit of the LunaGlob Russian mission. The western ellipse for the spacecraft landing in the crater Bogus� lawsky in the southern polar region of the Moon was investigated. The percentage of the shaded area was mea� sured in the images acquired with the LROC NAC camera with a resolution of ~0.5 m. Due to the close vicin� ity of the pole, it is difficult to build digital terr ain models (DTMs) for this region from the LROC NAC images. Because of this, the method described has been suggested. For the landing ellipse investigated, 52 LROC NAC images obtained at the Sun elevation from 4° to 19° were used. In these images the shaded portions of the area were measured, and the values of these portions were transferred to the values of the occurrence of slopes (in this case, at the 3.5�m baseline ) with the calibration by the surface characteristics of the Lunokhod�1 study area. For this area, the digital terrain model of the ~0.5�m resolution and 13 LROC NAC images obtained at different elevations of the Sun are available. From the results of measurements and the corresponding calibration, it was found that, in the studied landing ellipse, the occurrence of slopes gen� tler than 10° at the baseline of 3.5 m is 90%, while it is 9.6, 5.7, and 3.9% for the slopes steeper than 10°, 15°, and 20°, respectively. Obviously, this method can be recommended for application if there is no DTM of required granularity for the regions of interest, but there are highresolution images taken at different eleva� tions of the Sun.