  In this paper a new observer is introduced to estimate the Crystal Size
Distribution (CSD) only from the measurements of the solute concentration,
temperature and a model of the growth rate. No model of the nucleation rate is
needed. This approach is based on the use of a Kazantzis-Kravaris/Luenberger
observer which exponentially estimates functionals of the CSD. Then, the full
state is estimated by means of a Tikhonov regularization procedure. Numerical
simulations are provided. Our approach relies on an infinite-dimensional
observer, contrarily to the usual moment based observers.
