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

Abstract

Forest damage induced by bark beetle 
\nattacks can cause major economic losses in forest- 
\nry. Hyperspectral remote sensing data and state of 
\nthe art very high spatial resolution satellite data of- 
\nfer a great potential for assessing tree vitality. How- 
\never, a better understanding of the effects of vitality 
\ndecrease and its impact on the spectral behaviour of 
\nneedles is needed. Filling this knowledge gap can 
\nmake a significant contribution to improve the in- 
\nterpretation of remote sensing data. However, it is 
\nstill unclear which method for needle spectra col- 
\nlection is most suitable. In this work, two methods 
\nfor spectral reflectance measurements of Norway 
\nspruce needles using portable spectroradiometers 
\nwere tested and analysed: using a classical fore op- 
\ntic and a so-called contact probe. The spectral re- 
\nflectance data were evaluated with different statis- 
\ntical similarity measure techniques. Besides ana- 
\nlysing the measurements themselves, the methods 
\nwere compared in terms of their practicality. Fur- 
\nthermore, the impact of storage on the reflection 
\nbehaviour was investigated. The spectral measure- 
\nments were performed in the field as well as in a 
\nlaboratory and repeated three times during the 
\n2013 growing season. Based on the obtained results 
\nwe recommend measuring needle samples with the 
\ncontact probe of portable spectroradiometers.