On the variational data assimilation by a marine ecosystem model of NPZ type

Sur l'assimilation variationnelle de données par un modèle d'écosystème marin de type NPZ

Yann Leredde (1, 2) , Christine Lauer-Leredde (1) , Frederic Diaz (2)

1 LDL - Laboratoire Dynamique de la Lithosphère
2 LOB - Laboratoire d'océanographie et de biogéochimie

A variational data assimilation method is applied to a simplified marine ecosystem model of NPZ (Nutrient Phytoplankton Zooplankton) type, which implies five parameters. The method allows us to optimise these parameters by an iterative process of minimisation of a cost function which quantifies the quadratic discrepancy between observations and simulation results. The first part of this note describes how to obtain the adjoint model of the NPZ model allowing us to compute the gradient of the cost function relative to the parameters. Two experiments of artificial data assimilation then show the efficiency of this method, but also its limitations because of non-linearities and sensitivity problems of the model relative to the parameters.

Mots clés: Adjoint model; Identification of parameters; Marine ecosystem; Optimal control; NPZ model

Domaines: Biodiversité et Ecologie; Océan, Atmosphère; Océanographie

Yann Leredde, Christine Lauer-Leredde, Frederic Diaz. On the variational data assimilation by a marine ecosystem model of NPZ type. Comptes Rendus Géoscience, 2005, 337 (12), pp.1055-1064. ⟨10.1016/j.crte.2005.05.003⟩. ⟨hal-02061963⟩