“…Empirical [195] and conceptual models [13,179,181,[187][188][189]194] were the main focus at that stage. As it was not clear what type of data assimilation methods are most suitable for RS-SM assimilation during that period, various data assimilation approaches, including statistical correction [179,188,195], Newtonian nudging [179], variational data assimilation [194], the discrete Kalman filter (KF) [13] and the extended Kalman filter (EKF) [181,187,189,194], were examined. Pauwels et al [179,188] did some comparison and found that statistical correction resulted in reliable updating of the forecasting models and there was no need to use nudging.…”