Investigation of Lunar Impact Structures and Ridge Features by KAGUYA Altimetry (LALT) Data

The Laser ALTimeter (LALT) aboard a main orbiter of Japanese lunar explorer KAGUYA (SELENE) is a ranging instrument that measures the distance between the satellite and the lunar surface with accuracy of 5m by round trip time of the laser light every 1 second. Kaguya is in a polar orbit, the first global, precise, high-resolution topographic map has been obtained. Especially, previous experiments (ex. Clementine LIDAR) had not been gathered at high latitude regions (above 75-degree north and south). Our LALT measured that region for the first time. Using LALT data, we built a new lunar topographic mode and compared it with a previous model. As of LALT, the Unified Lunar Control Network 2005 (ULCN2005) was most precise lunar global topographic model based on a combination of Clementine images and a previous lunar control network derived from Earth-based & Apollo photographs, and Mariner 10, & Galileo images. Comparing our model with both ULCN2005 and Clementine LIDAR model, it is obviously shown that lunar topographic model would be totally (not only polar region, but also equatorial region) refined by our LALT model. LALT model can clarify the presence and shape of craters as well as large impact structure. Previously unresolved heights of central peaks of large craters are obtained. Several large impact structures in far side high land regions show multi-ring morphologies some of which were obscure in the previous map. LALT data clarified the presence of new ring structure around Moscoviense basin. The center of newly defined ring structure is offset from that of other Moscoviense rings. It means that, the new ring is not the third ring of Moscoviense, but it is predated impact structure. In near side, LALT data could express some tectonic ridges and rimas within the mare region.