FILTER 4DAn adjoint-free four-dimensional variational data

filter 4d A four-dimension (4D) bidirectional dital filter, having a minimum number of delay elements, is presented. This filter, besides having a minimum number of delay elements, also has an. A four-dimension (4D) bidirectional dital filter, having a minimum number of delay elements, is presented. This filter, besides having a minimum number of delay elements, also has an

filter 4d togel, We present a four-dimensional ensemble Kalman filter (4D-LETKF) that approximately and efficiently solves a variational problem similar to that solved by 4D-VAR,.