Some kind of approximate Bayes method. Utility unclear. There are more fashionable alternatives with less abstruse literature and more active researcher communities.
Chen, Yan, and Dean S. Oliver. 2013. “Levenberg–Marquardt Forms of the Iterative Ensemble Smoother for Efficient History Matching and Uncertainty Quantification.” Computational Geosciences 17 (4): 689–703.
Goldstein, Michael, and David Wooff. 2007. Bayes Linear Statistics: Theory and Methods. Wiley Series in Probability and Statistics. Chichester, England ; Hoboken, NJ: John Wiley.
Oliver, Dean S. 2022. “Hybrid Iterative Ensemble Smoother for History Matching of Hierarchical Models.” Mathematical Geosciences 54 (8): 1289–1313.
White, Jeremy T., Randall J. Hunt, Michael N. Fienen, and John E. Doherty. 2020. “Approaches to Highly Parameterized Inversion: PEST++ Version 5, a Software Suite for Parameter Estimation, Uncertainty Analysis, Management Optimization and Sensitivity Analysis.” USGS Numbered Series 7-C26. Techniques and Methods. Reston, VA: U.S. Geological Survey.