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. Twin experiments 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. (c) 2012 Elsevier Ltd. All rights reserved.