Solar induced fluorescence measurements using a field spectroradiometer Available to Purchase

This work analyses the capability of estimating solarinduced vegetation fluorescence with general purpose field spectroradiometers. The most common approach to measure vegetation fluorescence under field conditions is by means of the Fraunhoffer LineDepth (FLD) method. The objective of this work is to check the applicability of this method at the two oxygen absorption bands when using an ASD FieldSpec PRO spectrometer. To accomplish this goal, two types of measurements are acquired. The first one is the spectral curve of the leaf radiance, which is used by the FLD method and consists on the solar reflected light plus the induced vegetation fluorescence emission. The second measurement is the actual spectral curve of the solar induced fluorescence emission from plant leaves when filtering the incident solar radiation with a cyan filter. Based on these measurements some improvements in the FLD method are proposed to increase the accuracy of the retrieved values, which include more realistic hypotheses on the behaviour of both the reflectance and fluorescence curves over the O2 absorption bands. In addition, in order to assure that the fluorescence signal is in fact measurable with this instrumentation and method, the measurement of the Kautsky effect is used as an indicator of the suitability and accuracy of the setup.The obtained results show that fluorescence estimates using the 760 nm band are acceptable, reducing the dispersion in the estimated errors with respect to the standard FLD method, despite that the spectral resolution is not optimum. On the other hand, the 687 nm band has been found to provide unreliable values because the hypothesis about the baseline reflectance curve is not appropriate, resulting in a large bias in the absolute value of fluorescence, even when using the standard FLD method. However, this band is still sensitive to fluorescence changes. Therefore, it can be concluded that the improved FLD method can be used with a field spectroradiometer in the 760 nm with good radiometric sensitivity.