2.2.2. Spectral Library

Five different endmember classes were used to unmix the Rim Fire images: green vegetation (GV); non-photosynthetic vegetation (NPV), which includes dead needles, forest litter, bark senesced grass and other non-photosynthetically active plant material; soil, which includes bare soil and rock; char, which includes charred plant material and ash; and shade. Typical sources for endmembers include either spectra derived from the field, laboratory, or spectra derived from the imagery itself using pure pixels [49].

In this study, a combination of sources were used (Table 1). Field samples of charcoal, non-photosynthetic vegetation and substrate were collected and analyzed at the JPL spectroscopy lab [50]. Measurements in the 400–2500 nm spectral domain were obtained with an Analytic Spectral Devices (ASD) Full Range Spectrometer under artificial lighting conditions with an ASD Pro lamp. Reflectance was calibrated using a white Spectralon panel. We also used spectra collected from AVIRIS imagery, acquired on 26 June 2013 and 17 November 2013. To extract these spectra, polygons of areas composed solely of one of the four endmember classes (not including shade) were identified in the images. The spectra of all pixels within each polygon were extracted and labeled by endmember class. The spectral profile of each pixel was then manually reviewed to assure that it was consistent with the endmember class it was labeled as. To capture spatial scales that were not otherwise available in our analysis, an existing spectral library created from Wind River Research Forest (in Southern Washington state) was used [51]. This library included collections of leaves (branches) and tree bark, measured with an ASD in the field. Tree crowns measured in situ via a canopy crane were also included in this library. Although the spectra in the Wind River library were acquired in a different geographic location, many of the species and genera are common for both locations. Although Roberts et al. [51] also included stand level spectra measured with AVIRIS, these spectra were not included in our study.

**Table 1.** The number and origin of endmember used for the source spectral library. Analytic Spectral Devices is abbreviated as (ASD) and denotes field collected samples spectrally analyzed at a lab. Images acquired through Airborne Visible/Infrared Imaging Spectrometer are abbreviated as (AVIRIS). Spectra developed during a study in Wind River Research Forest [51] are denoted as Wind River. Green vegetation is abbreviated as (GV) and non-photosynthetic vegetation as (NPV).

