This initial definition was based on low-resolution images from Lunar Obiter missions. Later Earth-based radar estimates confirmed Sikorsky-Rittenhouse's status as a basin and placed the basin diameter at 319 km. However, the use of LOLA data have helped scientists to further define the diameter size to 275 km, which represents an 11% decrease in the original diameter estimate. LOLA's high density of measurements across the Moon allows its data to create the most accurate definition of lunar craters ever.
References:
1. Jones, N. and B. Steigerwald, (2010) "NASA's LRO Exposes Moon's Complex, Turbulent Youth," 03 June 2011.
2. Wilhelms, D.E, (1987) The Geologic History of the Moon, USGS Professional Paper 1348
3. Frey, H.V. (2010) Chapter 2, GSA Special Publication Recent Advances and Current Research Issues in Lunar Stratigraphy (in press).
4. Romine, G.C., and H.V. Frey, (2011) "Using LOLA Data to Test the Reality of Candidate Lunar Basins Derived from Older Data," 41st Lunar and Planetary Science Conference, Abstract 1188, March 1-5, The Woodlands, TX.