FILTER 4DAn adjoint-free four-dimensional variational data

filter 4dA 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 anA 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