Bidirectional and Spectral Reflectance Properties of the Cladina stellaris and Flavocetraria nivalis lichens and the Racomitrium lanuginosum moss

In this thesis we present a scientific investigation of the spectral and bidirectional reflectance properties of two lichen species, Flavocetraria nivalis and Cladina stellaris, and one moss, Racomitrium lanuginosum. The spectral and bidirectional characterizations were based on high-quality laboratory measurements made in the European Goniometer facility, at the Joint Research Center, Ispra, Italy. We found that the estimated reflectance factors were within 2% of their mean value, after corrections for an intensity drift in the illumination source, and non-Lambertian properties of the reference panel. We found that the spectral profile of the Racomitrium lanuginosum was similar to that of dry or stressed green vegetation. Moistened lichen canopies exhibited a higher reflectance factor than dry lichens in the visible and near-infrared spectral bands. Moistened moss however, had a lower reflectance than dry moss. We compared our laboratory measurements with in situ spectral field measurements, and found an excellent agreement. Our goniometric measurements showed that the lichens are strongly backscattering canopies in both the visible and near-infrared parts of the spectrum. The moss however, scattered isotropically in the visible part of the spectrum, whereas it was strongly backscattering in the near-infrared part of the spectrum. We characterized our experimental bidirectional reflectance factors of the targets by means of a parametric and a physical model. By means of a statistical analysis, we showed that the parametric model was superior in terms of numerical convergence and flexibility. We applied cross-validation and bootstrap techniques to assess the accuracy of reflectance factor estimates. Lastly we demonstrated the possibility of simulating the top-of-the-atmosphere lichen reflectance factors based on laboratory measurements, and we explained how these results can be used to identify areas with a lichen cover of av Landsat-5 TM scene