29 | | Generally, all three components are independent. In particular, the filters are implemented in the core part of PDAF. To combine the model and observational information one has to define the relation of the observations to the models fields (For example, model fields might be directly observed or the observed quantities are more complex functions of the model fields? In addition, the observations might be a~~vailable on grid points. If not,~~ interpolation is required.) In addition one has to define the relation of the state vector that is considered in the filter algorithms to the model fields. These relations are defined in separate routines that are supplied to the assimilation system by the user. These routines are called through a well-defined standard interface. To ease the implementation complexity, these user-defined routines can be implemented like routines of the model code. Thus, if a user has experience with the model, it should be rather easy to extend it by the routines required for the assimilation system. |

| 29 | Generally, all three components are independent. In particular, the filters are implemented in the core part of PDAF. To combine the model and observational information one has to define the relation of the observations to the models fields (For example, model fields might be directly observed or the observed quantities are more complex functions of the model fields? In addition, the observations might be at different locations than the model grid points so that interpolation is required.) In addition one has to define the relation of the state vector that is considered in the filter algorithms to the model fields. These relations are defined in separate routines that are supplied to the assimilation system by the user. These routines are called through a well-defined standard interface. To ease the implementation complexity, these user-defined routines can be implemented like routines of the model code. Thus, if a user has experience with the model, it should be rather easy to extend it by the routines required for the assimilation system. |