Reflectance spectra collected August 21, 2022, at Black Rock Desert, Nevada, with an ASD FieldSpecⓇ 4 Hi-Res NG spectroradiometer for calibration/validation of imaging spectrometer data

Reflectance data were collected using Malvern Panalytical ASD FieldSpec® 4 Hi-Res NG Spectroradiometers with custom VNIR gratings (hereafter referred to as ASD spectrometers) on August 21, 2022, at a field site on Black Rock Desert, Nevada, USA. A full description of all collection and processing steps is included in this data release as ‘BlackRockDesertNV_21aug2022_ProcessingSteps.pdf’. These data are useful for comparison with imaging spectrometer data collected from aircraft, e.g., AVIRIS-Classic (Vane and others, 1993), and from space, e.g., EMIT (Thompson and others, 2023; Green and others, 2021) and EnMAP (Storch and others, 2023). Because the field data have fine spectral resolution and were collected over a large area, they are applicable to calibration or validation of these and other airborne and spaceborne imaging spectrometers and multispectral sensors. Reflected sunlight was measured with the bare fiber (no fore optic), having a field of view of ~22 degrees, while traversing the area of the field site. Additional measurements of reflected artificial light were made at discrete sample points within the field site using an ASD Hi-Brite Contact Probe. Averages of relative reflectance spectra for the field site were computed separately from the sunlight and artificial light measurements. These averages were converted from relative reflectance to absolute reflectance by compensating for the absorption properties of the reference panel, a National Institute of Standards and Technology traceable Labsphere Spectralon® 99% reflective panel. Parts of the averaged artificial light spectrum were merged with the averaged sunlight spectrum in wavelength regions where atmospheric gases, e.g., water vapor, oxygen, and carbon dioxide, have strong absorption and the ASD spectrometers have low signal-to-noise ratio. To form the merged average absolute reflectance spectrum, segments of the averaged absolute reflectance from the artificial light measurements were scaled multiplicatively and merged with the averaged absolute reflectance from sunlight measurements. The merged spectrum is suitable for comparison with imaging spectrometer data across the full ASD wavelength range. At the field site, representative hand samples were collected. These samples were measured at the U.S. Geological Survey (USGS) laboratories in Denver, Colorado using an ASD spectrometer. In this data release we provide the following data files in the specified formats: 1. Raw ASD spectrometer binary files recorded on the spectrometer in ASD Indico format (.asd files; Malvern Panalytical, 2018), 2. Latitude, longitude coordinates, date and UTC times of acquisition, and other metadata for all recorded field spectra in comma separated value (CSV) format (.csv extension) 3. Average of the reflected sunlight measurements in text file (.txt extension), 4. Average of the artificial light measurements in text file (.txt extension), 5. Average of the laboratory measurements in text file (.txt extension), 6. Merged sunlight/artificial light spectrum in text file (.txt extension), 7. ASD spectrometer wavelength and bandpass (FWHM) parameters in text file, included with ASD measurements (.txt extension), 8. Bounding polygon of field site in Zip-compressed Keyhole Markup Language (KMZ) and shapefile vector formats (.kmz and .shp extensions), 9. Various photos of the field site, measurement techniques, and sky conditions in Joint Photographic Experts Group (JPEG) format (.jpg files).