Abstract

We use L1‐norm model regularization of |Br | component at the surface on magnetic monopoles bases and along‐track magnetic field differences alone (without vector observations) to derive high quality global magnetic field models at the surface of the Moon. The practical advantages to this strategy are the following: monopoles are more stable at closer spacing in comparison to dipoles, improving spatial resolution; L1‐norm model regularization leads to sparse models which may be appropriate for the Moon which has regions of localized magnetic field features; and along‐track differences reduce the need for ad‐hoc external field noise reduction strategies. We examine also the use of Lunar Prospector and SELENE/Kaguya magnetometer data, combined and separately, and find that the Lunar Prospector along‐track vector field differences lead to surface field models that require weaker regularization and, hence, result in higher spatial resolution. Significantly higher spatial resolution (wavelengths of roughly 25–30 km) and higher amplitude surface magnetic fields can be derived over localized regions of high amplitude anomalies (due to their higher signal‐to‐noise ratio). These high‐resolution field models are also compared with the results of Surface Vector Mapping approach of Tsunakawa et al. (2015, https://doi.org/10.1002/2014JE004785). Finally, the monopoles‐ as well as dipoles‐based patterns of the Serenitatis high amplitude magnetic feature have characteristic textbook patterns of Br and Bθ component fields from a nearly vertically downwardly magnetized source region and it implies that the principal source of the anomaly was formed when the region was much closer to the north magnetic pole of the Moon.

Document Type

Article

Publication Date

2020

Notes/Citation Information

©2020. American Geophysical Union. All Rights Reserved.

Digital Object Identifier (DOI)

https://doi.org/10.1029/2019JE006187

Funding Information 

We appreciate the great efforts of Lunar Prospector and SELENE/Kaguya teams for collecting valuable data analyzed in this study. We thank Ian Garrick‐ Bethell, an anonymous reviewer, and editors for their meticulous reviews. We are grateful to Sander Goossens and Erwan Mazarico of Goddard Space Flight Center for making available orbit positioning improved magnetic data from the SELENE/Kaguya extended mission. An undergraduate research student working with DR, Lillie Cole, generously allowed us to include her key result of modeling the Serenitatis magnetic feature prior to publication. We thank Kimberly Moore for discussions related to elastic net based sparse models. We also thank comments and suggestions on the manuscript made by Aspen Davis, Brooks Rosandich, and Ratheesh Kumar R. T. DR is grateful for the support from the NASA research grant NNX16AN51G which made this work possible. All of our preferred global and local models of magnetic field at the lunar surface are available in Ravat et al. (2020) provided in references.

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