Abstract
Abstract. This paper presents a preliminary result of crossover analysis and adjustment of Chang'E-1(CE-1) Laser Altimeter (LAM) data of the Moon for global and regional mapping applications. During the operation of Chang'E-1 from November 28, 2007 to December 4, 2008, the laser altimeter acquired 1400 orbital profiles with about 9.12 million altimetric points. In our experiment, we derived more than 1.38 million crossovers from 1395 ground tracks covering the entire lunar surface after eliminating outliers of orbits and altimetric points. A method of least-squares crossover adjustment with a series of basis functions of time (trigonometric functions and polynomials) is developed to reconcile the LAM data by minimizing the crossover residuals globally. The normal equations are very large but sparse; therefore they are stored and solved using sparse matrix technique. In a test area (0°N~60°N, 50°W~0°W), the crossover residuals are reduced from 62.1m to 32.8m, and the quality of the DEM generated from the adjusted LAM data is improved accordingly. We will optimize the method for the global adjustment to generate a high precision consistent global DEM, which can be used as absolute control for lunar mapping with orbital images.
Highlights
Chang’E-1 (CE-1) is the first lunar exploration mission of China, and one of its main tasks is to obtain the 3D images of the lunar surface
The root-meansquare (RMS) of the original crossover residual is 62.1m, and it is reduced to 36.8m after adjustment with a 2-order polynomial for each profile
Considering that trigonometric functions have been used in crossover adjustment, we developed the following four adjustment models for comparison purposes, among which the third models is the one used above
Summary
Chang’E-1 (CE-1) is the first lunar exploration mission of China, and one of its main tasks is to obtain the 3D images of the lunar surface. The Digital Elevation Model (DEM) of the lunar surface can be derived. Crossover differences (radial distances or heights) reflect the uncertainties in orbit determination (i.e., precision of spacecraft position and orientation) and the precision of laser ranging. Crossover analysis, which aims to adjust the crossover differences and force the planetary radii or height obtained at crossover locations to be consistent, is known as a powerful approach to improve orbit determination and derive more precise DEM. Crossover analysis has been widely used in satellite altimetry for earth observation, especially for the measurement of sea surface height. To the best of our knowledge, there is no crossover analysis and corresponding ground track correction for CE-1 LAM data so far
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