“…The model calibration methods typically involve a challenging minimization problem as this problem is usually ill-posed and the number of unknown model parameters can be very large. The ill-posedness of model calibration can be mitigated by reducing the number of parameters through an appropriate parameterization such as TSVD (Shirangi, 2011(Shirangi, , 2014Shirangi and Emerick, 2016;Bjarkason et al, 2017;Dickstein et al, 2017), ensemble-based methods (Rafiee and Reynolds, 2017;Rafiee, 2017;Rafiee and Reynolds, 2018), and PCA (Vo and Durlofsky, 2016). Durlofsky (2015, 2014) presented a differentiable PCA-based parameterization (O-PCA) that enables application of efficient gradient-based approaches for model calibration of complex channelized systems.…”