An NDVI-inspired reflectance index for detecting and characterizing tree resin with hyperspectral imaging

This study focuses on analyzing the reflectance characteristics of natural tree resin to develop a spectral index inspired by the normalized difference vegetation index (NDVI) method. The goal is to enable fast and straightforward detection of resin deposits on and around resin-secreting trees, such as spruces, as a method to detect parasitic infestations. To achieve this, we introduce the normalized resin difference index (NDRI), which combines reflectance values at 1688 nm with 1093 nm. This pairing has proven effective in distinguishing resin from common background materials such as bark and moss. Initial experiments also propose that the index could be a potential indicator of age. These capabilities, however, could not be clearly validated in a laboratory environment over a period of 50 days. While certain wavelengths corresponding to those in naturally aged resin samples showed consistent variability here, further investigation is needed to fully establish a connection between the observed spectral variations and the aging process of resin using a larger dataset under natural environmental conditions.