Detection of initial damage in Norway spruce canopies using hyperspectral airborne data

Abstract

Current broadband sensors are not capable of separating the initial stages of forest damage. The current investigation evaluates the potential of hyperspectral data for detecting the initial stages of forest damage at the canopy level in the Norway spruce (Picea abies (L.) Karst) forests of Czech Republic. Hyperspectral canopy reflectance imagery and foliar samples were acquired contemporaneously for 23 study sites in August 1998. The sites were selected along an air pollution gradient to represent the full range of damage conditions in even-aged spruce forests. The changes in canopy and foliar reflectance, chemistry and pigments associated with forest damage were established. The potential of a large number of spectral indices to identify initial forest damage was determined. Canopy hyperspectral data were able to separate healthy from initially damaged canopies, and therefore provided an improved capability for assessment of forest physiology as compared to broadband systems. The 673-724 nm region exhibited maximum sensitivity to initial damage. The nine spectral indices having the highest potential as indicators of the initial damage included: three simple band ratios, two derivative indices, two modelled red-edge parameters and two normalized bands. The sensitivity of these indices to damage was explained primarily by their relationship to foliar structural chemical compounds, which differed significantly by damage class.

Does the azimuth orientation of Norway spruce (Picea abies/L./Karst.) branches within sunlit crown part influence the heterogeneity of biochemical, structural and spectral characteristics of needles?

“…A shift of the REIP position towards shorter wavelengths, due to in chlorophyll concentration and changes in inner leaf structure, indicates early vegetation stress (Rock et al, 1988;Entcheva Campbell et al, 2004). Traditionally, the wavelength position of the REIP can be determined as a maximum value of the first derivative reflectance curve (Horler et al, 1983;Lamb et al, 2002).…”

“…Therefore, biochemical, structural and spectral foliar parameters are often used as ground truth for remote sensing vegetation monitoring analyses (e.g. Rock et al, 1988;Albrechtová et al, 2001;Entcheva Campbell et al, 2004). For proper interpretation and verification of remote sensing data and results regarding the physiological status of foliage, it is crucial to know if there is any kind of heterogeneity in such ground truth within the sunlit portion of a single crown.…”

Detection of Spatio-Temporal Changes of Norway Spruce Forest Stands in Ore Mountains Using Airborne Hyperspectral Imagery

“…Two temporal hyperspectral and ground-truth datasets were analyzed to study temporal changes of selected forest stands. First dataset represents ASAS (Airborne Solid-state Array Spectrometer) imagery and extensive in-situ data on forest biochemistry and biophysics acquired at the end of Norway spruce forest dieback phase [4][5]. A new hyperspectral image (Airborne Prism Experiment -APEX) as well as in-situ data were acquired in 2013 to assess forest physiological status after 15 years of regeneration.…”

“…In total, 38 even aged mature Norway spruce stands (21 at Přebuz and 17 at Kovářská sites) were selected for evaluation of tree physiological status using five-grade damage class scale as described in Table 1. The classification scheme is based on defoliation degree and presence of chlorosis rising from the practice used in the Czech Republic on that time [4]. In addition, five trees were selected at each stand for needle sampling to determine content of photosynthetic pigments (chlorophylls and carotenoids).…”

“…Significant advances have been made with the use of the first generation of airborne hyperspectral sensors enabling identification of not only significant forest damage, but also the very initial phases of vegetation stress. [3][4].…”