ETKF
ETKF stands for Ensemble Transform Kalman Filter, a deterministic variant of the Ensemble Kalman Filter (EnKF) designed for data assimilation in high-dimensional geophysical systems. It belongs to the family of ensemble square-root filters, and it updates the forecast ensemble by applying a linear transform to the ensemble perturbations, rather than perturbing observations. The ETKF was developed in the early 2000s as part of the ensemble square-root filter family.
In operation, a forecast ensemble is used to form ensemble anomalies around the mean. The method computes
ETKF has several variants, including local forms such as the Local Ensemble Transform Kalman Filter (LETKF),