Earth Planets Space, Vol. 60 (No. 4), pp. 365-373, 2008
M. Toyoshima1, H. Shibuya1, M. Matsushima2, H. Shimizu3, and H. Tsunakawa2
1Department of Earth Sciences, Kumamoto University, Kumamoto, Japan
2Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo, Japan
3Earthquake Research Institute, University of Tokyo, Tokyo, Japan
(Received March 1, 2007; Revised October 10, 2007; Accepted November 10, 2007; Online published April 9, 2008)
An objective scheme is presented for estimating the lunar crustal magnetic field from the LMAG (Lunar MAGnetometer) data of the SELENE ("KAGUYA") spacecraft. Our scheme improves the equivalent source method in three respects. The first improvement is that the source calculation is performed simultaneously with detrending. The second is that a great number of magnetic charges (magnetic monopoles) are used as the equivalent sources. The third is that the distribution of the magnetic charges is detremined by the damped least squares method, and the optimum smoothness is determined objectively by minimizing Akaike's Bayesian Information Criterion (ABIC). For testing the scheme, we apply it to the Lunar Prospector magnetometer data in the region centered at the Reiner Gamma magnetic anomaly. The magnetic field map at an altitude of 20 km is stably drawn from datasets for different altitudes (18 km and 34 km). The ABIC minimizing criterion successfully controls the smoothness due to the numerical damping and extracts as much information as possible from the given data. This scheme will help produce a coherent lunar magnetic anomaly map by integrating the observations from various altitudes of the SELENE and previous missions.
Key words: Equivalent source, ABIC, lunar crustal magnetic field, Reiner Gamma.