On-line Estimation of the Rate of Sap Flow in Plant Stems Using Stationary Thermal Response Data

The heat pulse method for the measurement of the rate of sapflow in plants suffers from two drawbacks, viz. the discontinuousnature of the measurements and the lack of a precise mathematicalformulation of the heat fluxes. To overcome these drawbacksa random noise heat signal has been used as an input and twosensor pairs have been used for the measurement. A model isgiven that employs the signal from one sensor pair as inputand the signal from the second pair as output of a heat transportsystem. Thus the adverse effects of radial heat conduction havebeen eliminated. Simulation models with the rate of sap flowas one of the parameters have been fitted to the stationaryresponse data with an on-line parameter optimization algorithm.The method has been validated in applications to artificialdata and to real data obtained from a plastic tube and fromtomato plants. Key words: Sap flow, Heat pulse method, Continuous measurement