A non-linear software sensor to monitor the internal nitrogen quota of phytoplanktonic cells

New techniques - called software sensors - issued from the non-linear autom atic control field and initially developed for non-linear chemical systems have been applied to a continuous culture of phytoplankton. A software sens or (or 'observer') combines an analytical differential equation based model and partial measurements of the system in order to estimate the non-measur ed state variables. It filters data and estimates the actual state of livin g systems, models of which are often rough approximations. The efficiency o f this approach is illustrated with a nitrate-limited chemostat experiment with the chlorophyceae Dunaliella tertiolecta performed in a computer contr olled fluctuating environment. (C) 2001 Ifremer/CNRS/IRD/Editions scientifi ques et medicales Elsevier SAS.