Het meten van lichtreflecties van gewassen

Abstract

Measurement of an object's reflectance spectrum can provide information on its nature and qualities. However, one should thoroughly take into account the fact that in general the reflectance spectrum does not only depend on the object itself, but also on the parameters defining the measurement conditions, like the spectral and spatial distribution of the incident light and the direction in which the reflectance is being measured. Therefore, when comparing reflectance spectra of different objects, it is necessary to keep the conditions of measurement as constant as possible. With the NIWARS-fieldspectrometer this has been realised by performing a comparative and simultaneous measurement on the object and a diffuse reflecting reference target which is exposed to the same illumination. The influence of variations in light intensity is suppressed in this way. By keeping the spatial distribution of the irradiation and the direction of observation constant, one can obtain a set of reflectance spectra among which variations can only be attributed to differences of the properties of the objects. However, it is possible that one is particularly interested in the influence of parameters like the solar position and the view angle on the reflectance spectrum of a certain object. With a spectrometer set-up, designed for this purpose, measurements have been executed. They provided insight into the magnitude of the systematic variations associated with multispectral scanning of crops.