Application of model reduced 4D-Var to a 1D ecosystem model

The model reduced 4D-Var (Vermeulen and Heemink, 2006) is investigated to test its feasibility in ecosystem application. Ecological models are known for their high nonlinearity and issues with non-differentiability. However, since the method is performed in the reduced space, the implementation of the adjoint of the tangent linear approximation of the original model is not required. xperiments are conducted in a 1D ecological model. Surface phytoplankton data are used, with 30% log-normally distributed measurement error. Three parameters are chosen for calibration. The method performs very well in the setup where a perfect initial condition is used, as well as for the combined parameter and initial condition estimation. A relatively well calibrated initial condition contributes to accurate parameter estimations. Not accounting for the wrongly assigned initial condition leads to incorrectly calibrated parameters.