Method Analysis for Collecting and Processing in-situ Hyperspectral Needle Reflectance Data for Monitoring Norway Spruce

Forest damage induced by bark beetle attacks can cause major economic losses in forest- ry. Hyperspectral remote sensing data and state of the art very high spatial resolution satellite data of- fer a great potential for assessing tree vitality. How- ever, a better understanding of the effects of vitality decrease and its impact on the spectral behaviour of needles is needed. Filling this knowledge gap can make a significant contribution to improve the in- terpretation of remote sensing data. However, it is still unclear which method for needle spectra col- lection is most suitable. In this work, two methods for spectral reflectance measurements of Norway spruce needles using portable spectroradiometers were tested and analysed: using a classical fore op- tic and a so-called contact probe. The spectral re- flectance data were evaluated with different statis- tical similarity measure techniques. Besides ana- lysing the measurements themselves, the methods were compared in terms of their practicality. Fur- thermore, the impact of storage on the reflection behaviour was investigated. The spectral measure- ments were performed in the field as well as in a laboratory and repeated three times during the 2013 growing season. Based on the obtained results we recommend measuring needle samples with the contact probe of portable spectroradiometers.