A theoretical study of an electrostatic multipole to assess the horizontaland vertical distribution of the in situ water content of vegetationcanopies

摘要

A theoretical study of an electrostatic multipole is presented. This instrument allows the non-destructive and in situ estimation of the water content of vegetation canopy horizontal layers from a measurement of their dielectric permittivities. The multipole is composed of four electrodes, two electrodes injecting an alternating current, while the two others measure a potential difference. A prototype instrument showed that good estimations of the wheat spike water content could be achieved. A simulation based on the finite element method is performed to study the response of the instrument for various wheat crop dielectric properties. Results show that the potential difference depends on the dielectric properties of the spikes and the stems, and that the soil influence is not significant. An improved configuration of the instrument, using two pairs of reception electrodes, is also simulated in order to be able to retrieve the spike and the stem permittivities. The inversion of the potential differences is realized by using an artificial neural network. The spikes' and the stems' permittivities can then be retrieved with a good accuracy (variances on estimated permittivities less than 0.01).