Abstract
In this study, a new data-adaptive network design methodology called k-SRBF is presented for the spherical radial basis functions (SRBFs) in regional gravity field modeling. In this methodology, the cluster centers (centroids) obtained by the k-means clustering algorithm are post-processed to construct a network of SRBFs by replacing the centroids with the SRBFs. The post-processing procedure is inspired by the heuristic method, Iterative Self-Organizing Data Analysis Technique (ISODATA), which splits clusters within the user-defined criteria to avoid over- and under-parameterization. These criteria are the minimum spherical distance between the centroids and the minimum number of samples for each cluster. The bandwidth (depth) of each SRBF is determined using the generalized cross-validation (GCV) technique in which only the observations within the radius of impact area (RIA) are used. The numerical tests are carried out with real and simulated data sets to investigate the effect of the user-defined criteria on the network design. Different bandwidth limits are also examined, and the appropriate lower and upper bandwidth limits are chosen based on the empirical signal covariance function and user-defined criteria. Also, additional tests are performed to verify the performance of the proposed methodology in combining different types of observations, such as terrestrial and airborne data available in Colorado. The results reveal that k-SRBF is an effective methodology to establish a data-adaptive network for SRBFs. Moreover, the proposed methodology improves the condition number of normal equation matrix so that the least-squares procedure can be applied without regularization considering the user-defined criteria and bandwidth limits.
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Data availability
The data sets used in this study are open-source data. The data sets generated during the current study are available from the corresponding author on reasonable request.
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Acknowledgements
The authors would like to thank the National Geodetic Survey for providing terrestrial, airborne and GPS\leveling data sets in the Colorado area and Prof. H. Duquenne for the availability of terrestrial and GPS\leveling data sets in the Auvergne area. The map figures were generated using the Generic Mapping Tools (GMT) (Wessel et al. 2019). The authors also would like to thank the editors and anonymous reviewers for their comments which improved the quality of the manuscript.
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RU designed and analyzed the algorithm, performed the calculations, compiled the figures and wrote the original manuscript. MOK supervised the entire work including the design and analysis of the algorithm. All authors read and approved the final manuscript.
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Ulug, R., Karslıoglu, M.O. A new data-adaptive network design methodology based on the k-means clustering and modified ISODATA algorithm for regional gravity field modeling via spherical radial basis functions. J Geod 96, 91 (2022). https://doi.org/10.1007/s00190-022-01681-2
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DOI: https://doi.org/10.1007/s00190-022-01681-2