MONITORING AND MODELING CANOPY WATER STORAGE AMOUNTS IN SUPPORT OF ATMOSPHERIC DEPOSITION STUDIES

Canopy water storage amounts were measured with a newly developed meas uring system based on the attenuation of a 10.26 GHz microwave signal. Every 5 min, vertical scans were made, over a period of 9 months. A p hysically based multi-layer interception model with empirical paramete rs was calibrated using a non-linear optimization technique. The calib rated model appeared to be capable of explaining up to 92% of the meas ured variance of water storage amounts for an independent validation p eriod when using on-site measurements of meteorological variables. The performance decreased only slightly to 89% when other input sets were used for this period. These were necessary to extrapolate the results to longer time series required for evaluating canopy resistances in t he study of deposition of airborne pollutants (Vermetten et al., Proc. 5th IPSASEP Conf., Vol. 3, 1992). The resemblance between measured th roughfall amounts and simulated results and the plausibility of the mo del parameters, although they were optimized without setting any limit s, enhances confidence in the model results.