Analytical Spectral Device Fieldspec3 foliar and soil reflectance survey, East River, CO 2023

Description

Abstract (En)

Fresh foliar and soil visible to shortwave infrared (VSWIR) spectra were measured in the field during a 2023 survey in Gunnison County, CO. This survey included the results reported here as well as physical sample collection and chemical analysis, results of which are reported separately. Sampling locations were selected based on metal hotspots identified using remote sensing data and foliar elemental data from the 2018 National Ecological Observatory Network (NEON) Airborne Observation Platform (AOP) imaging spectroscopy and lidar surveys in Gunnison County, CO. The samples collected in the 2023 survey from across the East River, Washington Gulch, Slate River, and Coal Creek watersheds include a mixture of vegetation predominantly shrub and trees, as well as meadow samples. Spectral measurements reported here were collected using an ASD Fieldspec3. Foliar and soil spectral measurements were cleaned and corrected for known jumps in reflectance across the three spectrometers for the FieldSpec3 instrument. This data package contains the corrected foliar and soil spectra in addition to the raw foliar, soil, and white reference data for this survey.

Methods

In 2023, we collected VSWIR field spectra at the leaf- and mineral-levels using an Analytical Spectral Devices (ASD) FieldSpec 3 spectroradiometer. Leaf spectra were collected on fresh samples. The instrument and lamp in the contact probe were turned on 30 minutes prior to collection to allow for the system to warm up and promote thermal stability. Then, the spectrometer was optimized, and a reflectance standard was measured using a Polytetrafluoroethylene (PTFE) reference disk supplied by Malvern Panalytical before collection at each sampling site. This procedure allowed for the sensor to be calibrated in radiance space and data to be subsequently collected in reflectance space using a leaf clip and contact probe for fresh foliar and soil samples, respectively. Three fresh foliar measurements were collected for each individual plant, and three soil measurements were collected at the base of each individual when possible. Spectra were taken before physical sample collection. Physical sample collection targeted fresh foliar and soil samples where spectra had been taken. For leaves, samples were collected from the top of the tree canopy and in foliar regions where associated 2018 National Ecological Observatory Network’s Airborne Observation Platform (NEON AOP) remotely sensed imagery designated sunlit portions of the individual. At the start, middle, and end of spectral collection at any given sampling area, a reference standard was taken. Notably, the 2023 atmospheric conditions did not allow for collection of spectra with a monopod and wand attachment. All ASD spectral measurements were taken at the individual leaf-level or mineral-level using a direct contact method with an independent light source. Foliar and soil spectral measurements were cleaned and corrected for the known jumps in reflectance across the three spectrometers in the FieldSpec3 instrument. 

Although field samples were taken on June 23rd-25th, no spectral sampling occurred on those days because the ASD computer malfunctioned. As a consequence, no soil spectra were taken for samples collected on those days even though physical samples were collected. Foliar samples collected on those days were stored in a refrigerator and foliar spectra were taken in the lab after the ASD computer was fixed on the evening of June 25th. The related files are labeled by physical sample collection date rather than spectral collection date. 

Raw spectra are in .asd file format and organized in subfolders with a labeling convention that details: (1) the sampling area and year, i.e., East River 2023 (ER23), (2) sample type, i.e., foliar (FO) or soil (SO), and finally, (3) sampling date (MMDDYY). The raw spectra files contain white reference data. Corrected spectra are in .csv file format with the same labeling convention; however, there is a letter (e.g. ‘a’, ‘b’, ‘c’) at the end of each file name that indicates different sampling locations for that day. For example, if there’s an ‘a’ and ‘b’ for a certain date, spectral collection occurred at two sampling locations that day, with ‘a’ collection preceding the ‘b’ collection time. Within the .csv files, the header columns contain the sample ID, cover type, latitude, longitude, location description. Wavelength values (nm) are provided in the header columns beginning in column six.