Physics
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufm.g53c..01a&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #G53C-01
Physics
1221 Lunar And Planetary Geodesy And Gravity (5417, 5450, 5714, 5744, 6019, 6250), 6250 Moon (1221)
Scientific paper
Currently, there are two generally accepted lunar control networks, the Unified Lunar Control Network (ULCN) and the Clementine Lunar Control Network (CLCN), both derived by M. Davies and T. Colvin at RAND. We will present the results of our work to reconcile the CLCN with the ULCN and improve the CLCN. The ULCN is based on images from the Apollo, Mariner 10, and Galileo missions, and Earth-based photographs. Network accuracy is relatively well quantified and varies from 100 m for points near Apollo landing sites to 3,000 m for points from Earth-based photographs. The network consists of 1,478 points with 87% of the points on the near side. The CLCN includes 271,634 points on 43,871 Clementine 750-nm images - the largest planetary control network ever computed. This network included 22 points from the ULCN concentrated in a 35° area on the nearside and the positions of these points were held fixed. The purpose of this network was to determine the geometry for the Clementine base map mosaic. The geometry of that mosaic was used to produce the Clementine UVVIS digital image model (DIM) and the Near-Infrared Global Multispectral Map of the Moon from Clementine. Through the extensive use of these products, they and the underlying CLCN in effect define the generally accepted current coordinate system for the Moon. After completion of the UVVIS DIM, it was noticed that horizontal errors of 15 km or more were present in the Clementine base map mosaic and therefore in the CLCN.
These errors seem to have arisen for several reasons, the three main reasons are that only a few (22) near side points were fixed to ULCN positions, the camera angles were unconstrained, and the tie points were all constrained to lie on a mass-centered sphere with a radius of 1736.7 km. First, in order to reconcile the CLCN with the ULCN, 1,385 points from the ULCN were visually identified on Clementine images that are part of the CLCN. In the least squares solution for the new control network (ULCN 2005), these points will be constrained by applying weights to their positions. The weights will be in proportion to the published accuracies of points in the ULCN. Second, the expectation for the CLCN was that NAIF SPICE data would provide horizontal accuracy better than 1 km, that residuals would be from small pointing errors, and the accuracy of the solution would approach the UVVIS pixel scale of a few hundred meters. This solution did not constrain the camera angles and the final solution did not check how much the camera angles changed. Unfortunately, the camera angles did change on average about 0.7° which resulted in movement of ground points by 15 km or more. In our new solutions camera angles are constrained to within 0.03° of their a priori (NAIF) values. Third, the main purpose of the CLCN was to produce Clementine image mosaics. During mosaic production the images were projected onto a sphere to remove camera distortions. The expectation was that this would cause the largest error for the oblique images, however, since most of the images were near vertical, the elevation difference would be negligible. In our new solution, radii of all tie points are constrained to within 1 - 5 km of values interpolated from lidar and Clementine stereo topography. The mean absolute average change is ~200 m, thus showing radii are being recovered at that average accuracy. This new solution will result in an improved control network solution, ULCN 2005. This network will provide horizontal and vertical control for over 273,000 points and will be the only lunar topographic model that is registered globally with horizontal control.
Archinal Brent A.
Kirk Randolph L.
Rosiek Mark R.
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