John M. Meyer Raymond F. Kokaly Todd M. Hoefen Evan M. Cox Gregg A. Swayze 20240806 1 tabular digital data Denver, Colorado U.S. Geological Survey Meyer, J.M., Kokaly, R.F., Hoefen, T.M., Cox, E.M., and Swayze, G. A.. Reflectance spectra collected August 16, 2022, at Smith Creek Valley, Nevada, with an ASD FieldSpecⓇ 4 Hi-Res NG spectrometer for calibration/validation of imaging spectrometer data: U.S. Geological Survey data release, https://doi.org/10.5066/P9E2TSDF IPDS Product number IP-147529 Additional Information about Originators: Meyer, J. M., https://orcid.org/https://orcid.org/0000-0003-2810-9414; Kokaly, R. F., https://orcid.org/https://orcid.org/0000-0003-0276-7101; Hoefen, T. M., https://orcid.org/https://orcid.org/0000-0002-3083-5987; Cox, E. M., https://orcid.org/https://orcid.org/ 0000-0002-1434-7000; Swayze, G. A., https://orcid.org/https://orcid.org/ 0000-0002-1814-7823. https://doi.org/10.5066/P9E2TSDF John M. Meyer 2023 tabular digital data David R. Thompson, Robert O. Green, Christine Bradley, Philip G. Brodrick, Eyal Ben-Dor, and others. On-orbit Calibration and Performance of the EMIT Imaging Spectrometer. Remote Sensing of Environment. 2023. DOI: https://doi.org/10.22541/essoar.168988432.29040205/v1 A full description of all collection and processing steps is included in this data release as: ‘SmithCreekPlayaNV_16aug2022_ProcessingSteps.pdf’. 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 16, 2022, at a field site in Smith Creek Valley, Nevada, USA. The ASD spectrometers used have a spectral range of 0.35 to 2.5 micronswith 2151 channels of data reported (Malvern Panalytical, 2018). 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 because atmospheric gases, e.g., water vapor, oxygen, and carbon dioxide, have strong absorption in parts of the measured wavelength region and the ASD spectrometers have low signal-to-noise ratio in parts of that wavelength range. 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. Merged sunlight/artificial light spectrum in text file (.txt extension), 6. Average of the laboratory measurements in text file (.txt extension), 7. Bounding polygon of field site in Zip-compressed Keyhole Markup Language (KMZ) and shapefile vector formats (.kmz and .shp extensions), 8. Various photos of the field site, measurement techniques, and sky conditions in Joint Photographic Experts Group (JPEG) format (.jpg files). ASD spectrometer data were collected in the field 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. References Cited Clark, R.N., Swayze, G.A., Livo, K.E., Kokaly, R.F., King, T.V., Dalton, J.B., Vance, J.S., Rockwell, B.W., Hoefen, T., and McDougal, R.R., 2002, Surface reflectance calibration of terrestrial imaging spectroscopy data: a tutorial using AVIRIS, in Proceedings of the 10th Airborne Earth Science Workshop, Jet Propulsion Laboratory Pasadena, CA., p. 43-64. Green, R.O., Thompson, D.R., and Team, E., 2021, NASA's Earth Surface Mineral Dust Source Investigation: An Earth Venture Imaging Spectrometer Science Mission, in 2021 IEEE International Geoscience and Remote Sensing Symposium IGARSS, Brussels, Belgium, IEEE, p. 119-122. DOI: https://doi.org/10.1109/IGARSS47720.2021.9554217 Kokaly, R., (2011), PRISM: Processing routines in IDL for spectroscopic measurements (installation manual and user's guide, version 1.0), U.S.Geological Survey Open-File Report 2011–1155. DOI: https://doi.org/10.3133/ofr20111155. Kokaly, R.F., Clark, R.N., Swayze, G.A., Livo, K.E., Hoefen, T.M., Pearson, N.C., Wise, R.A., Benzel, W.M., Lowers, H.A., & Driscoll, R.L., (2017a), USGS Spectral Library Version 7, US Geological Survey Data Series 1035, 61. DOI: https://doi.org/10.3133/ds1035. Kokaly, R.F., and Skidmore, A.K., 2015, Plant phenolics and absorption features in vegetation reflectance spectra near 1.66 μm: International Journal of Applied Earth Observation and Geoinformation, v. 43, p. 55-83. DOI: https://doi.org/10.1016/j.jag.2015.01.010 Malvern Panalytical, 2018, ASD FieldSpec® 4 Hi-Res NG Spectroradiometer, v. 2022, https://www.malvernpanalytical.com/en/products/category/near-infra-red-spectrometers, Retrieved December, 2022. Storch, T., Honold, H. P., Chabrillat, S., Habermeyer, M., Tucker, P., Brell, M., ... & Fischer, S. (2023). The EnMAP imaging spectroscopy mission towards operations. Remote Sensing of Environment, 294, 113632. DOI: https://doi.org/10.1016/j.rse.2023.113632 Thompson, D. R., Green, R. O., Bradley, C., Brodrick, P.G., Ben Dor, E., and others. On-orbit Calibration and Performance of the EMIT Imaging Spectrometer. Remote Sensing of Environment. 2023. DOI: (Not yet assigned). Vane, G., Green, R.O., Chrien, T.G., Enmark, H.T., Hansen, E.G., Porter, W.M., 1993. The airborne visible/infrared imaging spectrometer (AVIRIS). Remote Sens. Environ. 44, 127-143, doi.https://doi.org/10.1016/0034-4257(93)90012-M 20220821 ground condition Complete None planned -117.447785 -117.445952 39.326539 39.325250 ISO 19115 Topic Category environment USGS Thesaurus hyperspectral imaging geophysics camera calibration remote sensing GGGSC Geology, Geophysics, and Geochemistry Science Center MRP Mineral Resources Program USGS U.S. Geological Survey Earth Mapping Resources Initiative EarthMRI USGS Metadata Identifier USGS:64b59262d34e70357a2aee11 Common Geographic Areas United States of America Nevada Lander County Smith Creek Valley None. Please see 'Distribution Info' for details. None. Users are advised to read the dataset's metadata thoroughly to understand appropriate use and data limitations. John M. Meyer USGS Geophysicist mailing

Box 25046 MS 973

Denver Colorado 80255 USA 303-236-3531 jmmeyer@usgs.gov No formal attribute accuracy tests were conducted No formal logical accuracy tests were conducted Data set is considered complete for the information presented, as described in the abstract. Users are advised to read the rest of the metadata record carefully for additional details. No formal positional accuracy tests were conducted No formal positional accuracy tests were conducted Step 1 Selection of Field Site The field site, a playa located in Smith Creek Valley, is in central Nevada, approximately 40 km SSW of Austin, NV. It was selected based upon many factors, including, accessibility, expected temporal invariance, large area, low topographic relief, high albedo, absence of strong spectral features, and relative uniformity of spectral shape, following Clark and others (2002). Upon arrival at the field site on August 16, 2022, a rectangular polygon measuring 150 m east-west by 130 m north-south was established using handheld GPS units. This rectangle formed the perimeter of the field site and was delineated using small orange cones to provide a frame of reference for the field crews during the measurement process (see the included files; ‘SmithCreekValleyNV_16aug2022_BoundingPolygon_kmz.kmz’ ‘SmithCreekValleyNV_16aug2022_BoundingPolygon_shp.shp’, and ‘SmithCreekValleyNV__16aug2022_BoundingPolygon.csv’ ) for field site corner locations). The surface of the field site was very consistent, with areas of unbroken surfaces of variable size, separated by shallow (~5mm) and narrow (1-2mm) mud cracks. Images captured at the vertices of the polygon (‘SmithCreekValleyNV_16aug2022_SitePhotoNEcorner_1.jpg’, ‘SmithCreekValleyNV_16aug2022_SitePhotoSEcorner.jpg’, 'SmithCreekValleyNV_16aug2022_SitePhotoSWcorner.jpg’, ‘SmithCreekValleyNV_16aug2022_SitePhotoNWcorner.jpg’, ) showing surface conditions of the calibration site are included in this data release. An image captured near the center of the calibration site polygon (‘SmithCreekValleyNV_16aug2022_SitePhotoSiteCenter.jpg’) and overview images of the calibration site captured from the northeast corner of the bounding polygon (‘SmithCreekValleyNV_16aug2022_SitePhotoNEcorner_2.jpg’, ‘SmithCreekValleyNV_16aug2022_SitePhotoNEcorner_3.jpg’, ‘SmithCreekValleyNV_16aug2022_SitePhotoNEcorner_4.jpg’) showing the surface conditions of the calibration site are also included in this data release. 2022 Step 2 Pre-collection Wavelength Check Field spectrometers may experience inadvertent rough handling and shocks during transport and field use. They also have moving parts that can wear over time. As a result, there is the potential that the wavelength positions of spectrometers channels may shift. In past monitoring of ASD spectrometers, these shifts have been observed as either a consistently positive shift across the full wavelength range (to longer wavelength), a consistently negative shifts across the full wavelength range (to shorter wavelength), or a roughly linear change in value (e.g., negative shift at the shorter wavelengths of a detector range to positive shift at longer wavelengths of a detector range, and vice versa). To ensure proper reporting of the wavelength of the collected field spectra, a laboratory wavelength check was performed before the deployment of a spectrometer for the field campaign. The procedure to wavelength check an ASD spectrometer is summarized as follows: A. Preventative maintenance or servicing by the manufacturer results in the generation of new calibration files by the manufacturer. The wavelength calibration file is customized for each ASD spectrometer. Therefore, after servicing or maintenance, we measure reflectance spectra of three internal standards and determine benchmark positions for 24 absorption features in their spectra. These internal standards are three Labsphere multi-component rare earth element doped spectralon pucks, each with a thin, clear Mylar plastic sheet on top (designated as a mcreemylar pucks). These absorption features are distributed through the wavelength ranges of the three ASD detectors, ten in the visible-near infrared (VNIR detector; covering 0.35 to 1.0 m), five in the first shortwave infrared detector (SWIR1; covering 1.001 to 1.8 m), and nine in the SWIR2 detector (covering 1.801 to 2.5 m). Functions of the US Geologic Survey’s Processing Routines in IDL for Spectroscopic Measurements (PRISM) software (Kokaly, 2011) are used to compute the benchmark wavelength positions of the 24 absorption features in the average spectra of mcreemylar pucks used in the lab (mcreemylar8782 and mcreemylar8784) and of a mcreemylar puck that is taken to the field (mcreemylar1332). B. Subsequent to the establishment of benchmark positions and prior to deployment to the field, a laboratory mcreemylar puck is measured and a PRISM function is used to check the wavelength positions of 24 selected absorption features in the average spectrum of the recorded measurements of the internal standard. The positions of the features were compared to the benchmark positions. The mean absolute error and average difference in the wavelength positions were computed for each of the three detectors in the spectrometer. If those differences were less than the threshold tolerance of 0.5 nm, the spectrometer is judged to be functioning within expected specifications. The lab wavelength check made before the field collection for ASD spectrometer serial number 18388, calibration number 8 (used to measure reflected sunlight; hereafter referred to as ASD18388-08) was done on August 10, 2022. A lab wavelength check was performed on ASD spectrometer serial number 18594, calibration number 7 (used to measure reflected artificial light; hereafter referred to as ASD18594-07) on August 10, 2022. Both spectrometers passed the lab wavelength check. A full description of procedures followed to wavelength check ASD spectrometers can be found in ‘MRP-SPECLAB-SOP-08.02 MEASURING REFERENCE STANDARDS.pdf’, included in this data release. 2022 Step 3 Measurement of Reflected Sunlight Reflected sunlight data were collected using ASD18388-08 equipped with the ASD spectrometer bare optical fiber (no fore optic) having an approximate angular field of view of 22 degrees. The ASD spectrometer was turned on 2 hours prior to the start of field measurements to warm up the system and improve thermal stability in the instrument at the start of and throughout the measurement period. During the measurement period, the ASD spectrometer settings (integration times and gain factors) were occasionally re-optimized to account for changing illumination levels and sky conditions. A 13.5 x 13.5 cm, square, National Institute of Standards and Technology traceable Labsphere Spectralon® 99% reflective reference panel (Spectralon panel), was used for optimization of the ASD spectrometer’s detectors. Measurement of the Spectralon reflectance standard (referred to hereafter as the ‘white reference procedure’) was repeated at least every 10 minutes, or more frequently, to account for changing illumination levels, or atmospheric variability. The controlling software for the ASD spectrometer has separate functions to optimize the spectrometer and to collect a white reference. It is not required to optimize the ASD spectrometer settings every time the white reference procedure is performed. Optimization is required when any of the detectors in the ASD spectrometer become saturated, or when illumination levels have changed significantly. A description of the Spectralon panel used in this contribution can be found in the USGS’s Spectral library (Kokaly and others, 2017), which is available at https://pubs.er.usgs.gov/publication/ds1035. Metadata for the Spectralon panel used in this contribution may be found at https://crustal.usgs.gov/speclab/data/HTMLmetadata/Spectralon99WhiteRef_LSPHERE_ASDFRa_AREF.html, while a zip file containing ASCII data of the spectrum may be found at https://crustal.usgs.gov/speclab/QueryAll07a.php?quick_filter=spectralon. Procedures to calibrate the ASD spectrometer using a known white reference are described in Clark and others (2002). Recent modifications to these procedures by USGS Spectroscopy Lab (https://www.usgs.gov/labs/spectroscopy-lab) personal include the use of a custom made ‘spectral staff’ (see included spectral_staff_technique.jpg). The spectral staff holds the Spectralon panel and the ASD spectrometer bare optical fiber in a stable and repeatable position, eliminating variations in the optical fiber view port to Spectralon panel distance and viewing angle. The operator installs the optical fiber in the receiver at the top of the spectral staff. This holds the view port of the optical fiber perpendicular to and 10 cm from the Spectralon panel. The operator then holds the staff plumb, with the receiver arm perpendicular to the sun incident angle during the optimization and white referencing procedures. Extending the telescoping segments of the spectral staff allows the operator to position the Spectralon panel above their head. This reduces any reflections from the operator or their clothes onto the white reference panel. The controlling software for the ASD spectrometer allows the user to set the number of measurements to be averaged for each recorded file for the target and the number of white reference measurements averaged during the white reference procedure. An ASD spectrometer measurement takes 0.1 seconds to collect; thus, increasing the number of measurements that are co-averaged for each recording increases the integration time required between recorded spectra. The settings for target and white reference measurement are chosen depending upon a variety of factors, the most critical being the stability of the atmosphere and illumination during the collection period. If the atmosphere is stable and the solar elevation is not changing rapidly, the number of measurements in the recorded spectra and white reference can be increased. With partly cloudy conditions and changing solar elevation angles in the late morning and early afternoon, the number of measurements co-averaged should be decreased and the white reference procedure should be performed more frequently. To reduce noise in the final averaged spectrum, the number of white reference measurements collected during each white reference procedure should be a minimum of twice the number of spectra averaged for each target measurement, regards of the number of spectra to be averaged for each measurement. For the reflected sunlight data contained in this data release, 150 spectra were averaged for each recorded spectrum of the target surface of the site (i.e.,15 second integration period), with 300 white reference measurements taken during each white reference procedure (i.e., 30 second integration period). Doing this keeps the signal-to-noise ratio of the white reference measurement average much higher than in any individual target measurement, thus assuring that any noise imparted by correction to absolute reflectance using the white reference measurements is a small fraction of that associated with the target measurement. Ideally, reflected sunlight data were collected by holding the bare optic fiber in a nadir pointing direction approximately 1.1 meter off the surface of the field site. When held static at this height the ASD measures a circular area with approximately 21.4 cm radius (42.8 cm diameter). The operator positioned the optical fiber as far as possible from their body with their arm straight out to the side of their body, with their body oriented so that arm was towards the sun. This technique is demonstrated in the left portion of the included ‘probe_fiber_optic_collection_techniques.jpg’ image. The operator then traversed the field site at a walking pace, continuously recording spectra which were written as ASD binary .asd files. In practice, the fiber optic is held at shoulder height to waist height of the spectrometer operator, approximately 1 to 1.5 m, depending on the height of the operator, resulting in a swath width of ~20 to 30 cm. Real-time visual monitoring of the collected spectra allowed the operator to monitor the magnitude of atmospheric residuals in spectra being recorded. The white reference procedure was repeated every ten minutes or more frequently when the magnitude of the residuals were judged to be large on the displayed plot of the most recently collected spectrum. Solar noon on the day of the collection was 12:54 PM local time (19:54 Coordinated Universal Time, UTC), the solar azimuth was 180.34° and the solar elevation was 64.22° at solar noon. Reflected sunlight data were collected from 11:18 AM local time (18:18 UTC) to 12:22 PM local time (19:22 UTC). The solar azimuth was 134.18° and the solar elevation was 56.77° at the beginning of the measurement period. The solar azimuth was 162.50° and the solar elevation was 63.28° at the end of the measurement period. The sky condition at the start of the measurement period was mostly clear, with broken cumulus approximately 1000 m above ground level occupying approximately 10% of sky (see ‘SmithCreekValleyNV_16aug2022_SitePhotoCloudConditions.jpg’ included in this data release). Cloud cover increased during the measurement period, to the point that measurements were halted prior to solar noon. A total of 169 reflected sunlight measurements were recorded. After review of the recorded spectra and elimination of recorded white reference panel measurements, spectra with large atmospheric residuals, and spectra with abnormal reflectance levels, 126 spectra were used to compute the average reflected sunlight spectrum (see Step 8). Locations of the recorded reflected sunlight measurements were not recorded due to an equipment malfunction. A directory ‘SSmithCreekValleyNV_16aug2022_ASDsun_RAWbinary’, containing the raw, binary ASD reflected sunlight spectra in ASD Indico file format is included in this data release. 2022 Step 4 Measurement of Reflected Artificial Light Reflected artificial light data were collected using ASD18594-07 equipped with an ASD Hi-Brite Contact Probe (hereafter referred to as the ‘contact probe’). The ASD spectrometer was turned on for at least 2 hours prior to the start of field measurements to warm up the system and improve thermal stability in the instrument at the start of and throughout the measurement period. The lamp in the contact probe was turned on at least one hour prior to the collection of spectra. The spectrometer was optimized, and a white reference measurement was taken prior to the collection of spectra. A Polytetrafluoroethylene (PTFE) puck supplied by Malvern Panalytical with the contact probe was used as the white reference. Reflected artificial light data were collected by holding the contact probe on the surface of the target and within the operator’s shadow thus reducing the introduction of stray sunlight into the contact probe measurement. This technique is demonstrated in the right portion of the included probe_fiber_optic_collection_techniques.jpg image. The operator traversed the field site stopping to record two measurements of the same spot at approximately 15-meter intervals. The operator cleaned the lens of the contact probe after collection of the two measurements and prior to collecting measurements at a new location. For the reflected artificial light data contained in this data release, 20 spectra (2 second integration) were averaged for each measurement, with 40 white reference spectra (4 second integration) taken during each white reference procedure. Traverses were made while walking in a roughly ‘X’ pattern from the NE corner to the SW corner and then from the NW corner to the SE corner. During the measurement period, the spectrometer was occasionally re-optimized using the PTFE puck. The white reference procedure was repeated at least every 10 minutes using the PTFE puck as the white reference. A total of 124 contact probe spectra were recorded. After eliminating any recorded white reference measurements, spectra with abnormal spectral shapes, and spectra with abnormal reflectance levels, 116 spectra were used to compute the average reflected artificial light spectrum (see Step 8). Locations of all recorded reflected artificial light measurements are logged in ‘SmithCreekValleyNV_16aug2022_ASDprobe_LatLonEtc.csv’ included in this data release. A directory ‘SmithCreekValleyNV_16aug2022_ASDprobe_RAWbinary’, containing the raw, binary ASD reflected artificial light spectra in ASD Indico file format is included in this data release. 2022 Step 5 Collection of Hand Samples A representative, composite sample of the surface material of the field site was collected for further analysis in USGS laboratories using spectrometers. The approximately 1 kg sample was collected while traversing the field site in an hour-glass pattern, with a small subsample taken approximately every 15 meters during the traverse. The composite sample was collected in a heavy-duty plastic zip-lock bag, which was labeled with the sample number, site name, latitude and longitude of the center of the field site, and the date of the collection. 2022 Step 6 Field-Based Wavelength Check During field campaigns, periodic checks are performed on the ASD spectrometers to confirm accurate wavelength values for the collected data. The procedure to wavelength check an ASD spectrometer in the field is summarized as follows: A. A mcreemylar field puck is measured using either reflected sunlight or a contact probe (artificial light). Subsequently, a PRISM function is used to compute the wavelength positions of 15 selected absorption features in the average spectrum of the recorded measurements of the mcreemylar field puck. Seven of these features are in the VNIR range, three in the SWIR1 range, and five in the SWIR2 range. Compared to the lab check of 24 absorption positions (see Step 2-A), the field check of spectrometer wavelength excludes nine absorption features that are weak, in the lower signal-to-noise ratio parts of ASD range, or within or near atmospheric absorption features. B. The feature positions computed for the averaged field data of the mcreemylar puck are compared to the benchmark positions established after receipt of the spectrometer following preventative maintenance or servicing by the manufacturer (as described in Step 2-A). The mean absolute error and average difference in the wavelength positions were computed for each of the three detectors in the spectrometer. If those differences were less than the threshold tolerance of 0.5 nm, the spectrometer is judged to be functioning within expected specifications. If time and conditions allow, best practice is to measure the mcreemylar field puck on-site each day an ASD spectrometer is used in field, immediately before or after the collection of the site spectra. In practice, such checks are performed periodically during the course of the field session. For the ASD18388-08, a field check was made and passed on August 18, 2022, two days after measurement of the field site. The ASD18594-07 also passed its field wavelength check on August 18, 2022. 2022 Step 7 Post-Field Wavelength Check After returning from a field campaign, a laboratory wavelength check is again performed. The check follows the procedure described in Steps 2-A and 2-B. The post-field wavelength check for ASD18388-08 (used to measure reflected sunlight) was done on August 31, 2022. The check of ASD18594-07 (used to measure reflected artificial light) was done on September 2, 2022. Both spectrometers passed their post-field work wavelength check. 2022 Step 8 Removal of Detector Offsets, Conversion to Absolute Reflectance, and Averaging of ASD Spectrometer Data Following procedures described in Kokaly and Skidmore (2015), averaging of spectral measurements was performed using functions in PRISM. Averaging of ASD spectrometer measurements consist of the following steps: 1. Plotting of spectra and visual inspection and intercomparison to identify spectra with anomalous reflectance levels, strong atmospheric residuals, and/or spectral artifacts. Check field notebook for any comments on spectral measurements that may indicate which spectra should be excluded from the average. Excluded spectra are not processed in the following steps. 2. Averaging of remaining relative reflectance measurements. 3. Removal of ASD spectrometer detector offsets. 4. Conversion of ASD spectrometer relative reflectance average to absolute reflectance. This step involves multiplying the averaged, offset-corrected, relative reflectance for the site by the reflectance of the reference panel. For these data a 99% reflective Spectralon panel was used. Note; the Spectralon panel is described in Step 3, with links to the reflectance spectrum of the panel. Included in this data release are the results from applying these steps to generate an average of the absolute reflectance of the field site measured using sunlight (‘SmithCreekValleyNV_16aug2022_ASDsun_AVGspectrum.txt’) and an average of the absolute reflectance of the site measured using an artificial light source (‘SmithCreekValleyNV_16aug2022_ASDprobe_AVGspectrum.txt’). 2022 Step 9 Laboratory ASD Spectrometer Measurements The collected sample was measured in the USGS Spectroscopy Lab using ASD18594-07. The ASD spectrometer and artificial illumination source were turned on 2 hours prior to the start of laboratory measurements to warm up the system and improve thermal stability in the instrument at the start of and throughout the measurement period. The fiber optic cable of the ASD was placed in a holder approximately 10 cm above the sample and pointing 30 degrees off-nadir. The representative sample of the calibration site was centered within the ASD field of view on a rotation stage, which turned slowly during the measurement process. The viewing plane of the fiber optic cable was oriented orthogonal to the illumination plane of the artificial illumination source, to reduce specular reflection. The light source was three tungsten halogen bulbs (two without protective UV coating) oriented approximately 20 degrees off-nadir. The spectrometer was optimized, the white reference procedure was performed, and 20 spectra were recorded. This procedure was repeated 4 times using different representative samples, resulting in a total of 80 recorded spectra. Each recorded file was a co-average of 300 spectra (30 second integrations). During the spectrometer optimization procedure, the dark current setting was 100 for this shutterless ASD spectrometer. During the white reference procedure, 1200 white reference spectra were averaged (120 second integration). A description of procedures followed to measure samples in a laboratory using an ASD spectrometer can be found in ‘MRP-SPECLAB-SOP-02.02 MEASURMENTS WITH THE ASD SPECTROMETERS.pdf’, included in this data release. A directory ‘SmithCreekValleyNV_16aug2022_ASDlaboratory_RAWbinary’, containing the raw, binary ASD lab spectra in ASD Indico file format is included in this data release. The directory contains 80 measurements having a file name convention of ‘SmithCreekPlayaAug2022*.asd’. Conversion of native ASD spectrometer binary data to absolute reflectance, removal of detector offsets, and averaging of spectral measurements were performed as described in Step 8. The average of the absolute reflectance of the laboratory measurements (‘SmithCreekValleyNV_16aug2022_ASDlaboratory_AVGspectrum.txt’) is included in this data release in ASCII text file format. 2022 Step 10 Merging of Sunlight and Contact Probe/Lab Spectra A function in PRISM is used to merge the reflected sunlight and probe data. In wavelength regions of atmospheric absorption, segments of the averaged absolute reflectance from the artificial light measurements are scaled multiplicatively and merged with the averaged absolute reflectance from sunlight measurements, to form a continuous, merged average absolute reflectance spectrum. If the field site has a rough surface, the contact probe may not be useable in the field and the sunlight measurement should be merged with the laboratory reflectance measurement of the field sample. For this field site, the reflected sunlight spectrum was merged with the contact probe measurement. Overall reflectance of the merged average was high (>60% from 0.75 to 1.8 m). The merged spectrum has a moderate strength absorption feature centered near 2.209 µm with a weaker shoulder absorption centered near 2.248 µm, and a weak absorption feature centered near 2.300 µm, likely caused by the clay minerals in the playa surface. An ASCII text file (‘SmithCreekValleyNV_16aug2022_ASDmergedSpectrum.txt’) containing this merged average is provided in this data release. The sunlight spectrum has a reflectance level approximately 5% higher than the average of the laboratory measurements. The reflectance level of the sunlight spectrum is considered more representative of a measurement made from an airborne or satellite-based sensor. For that reason, the segments of the artificial light spectrum are scaled to the reflectance level of the sunlight spectrum. A slight dip in the merged spectrum is present at 1.807 µm which is not present in the laboratory measurement of the sample. This small dip is likely an artifact from the contact probe measurement. Upturns in the artificial light spectra (contact probe and laboratory) are present shortward of approximately 0.38 µm. This is a stray light artifact caused by the spectrometer and the artificial illumination, which is relatively weak in the ultraviolet region. The long wavelength light leaks inherent in diffraction grating spectrometers such as the ASD spectrometer impart a signal at shorter wavelengths, which is evidenced by the upturn in the spectrum shortward of approximately 0.38 µm. Solar illumination is strong at short wavelengths and the upturn due to stray light is not evident in the averaged sunlight spectrum nor in the merged spectrum. 2022 Point Entity point 298 0.00001 0.00001 Decimal degrees World Geodetic System 1984 (WGS 84) WGS_1984 6378137.0 298.257223563 SmithCreekValleyNV_16aug2022_ASDprobe_LatLonEtc.csv Comma Separated Value (CSV) file containing data. Producer Defined SPECFILE File Name Producer Defined spd0715 Name Producer defined SPEC_REC Record Number Producer Defined 27 765 SPECTITLE Record Name Producer Defined smith creek playa aug 2022 probe Name Producer defined MEAS_DATE Measurement Date Producer Defined 8/16/2022 Date Producer defined MEAS_TIME Measurement Time Producer Defined Time of Measurement GPS_LAT Measurement Latitude Producer Defined 39.32525 39.32648 Degrees GPS_LON Measurement Longitude Producer Defined -117.44778000000001 -117.44596000000001 Degrees GPS_DATUM Datum Used Producer Defined WGS-84 Name Producer defined INSTRUMENT Spectrometer ID Producer Defined 18594-7 ID Producer defined ASD_FILE ASD File name Producer Defined ASD File name The files 'SmithCreekValleyNV_16aug2022_ASDsun_AVGspectrum.txt',and 'SmithCreekValleyNV_16aug2022_ASDprobe_AVGspectrum.txt', contain in-situ spectral measurements of the Smith Creek Valley field site. The file 'SmithCreekValleyNV_16aug2022_ASDsmergedspectrum.txt', contains a merged spectrum of the 'SmithCreekValleyNV_16aug2022_ASDsun_AVGspectrum.txt',and 'SmithCreekValleyNV_16aug2022_ASDprobe_AVGspectrum.txt', measurements. The 'SmithCreekValleyNV_16aug2022_ASDlabortory_AVGspectrum.txt' contains laboratory spectral measurements made in USGS laboratory of the Smith Creek Field site sample. The ASD FieldSpec NG collects 2150 channels of data in the region from 0.350 to 2.499 microns. Absolute reflectance data for each channel is reported on a scale of 0 to1. Raw ASD data are binary ASD files and consist of sunlight and probe data. File format: ASD Indico. GS ScienceBase U.S. Geological Survey mailing address

Denver Federal Center, Building 810, Mail Stop 302

Denver CO 80225 United States 1-888-275-8747 sciencebase@usgs.gov Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. Digital Data https://doi.org/10.5066/P9E2TSDF None 20240806 John M. Meyer U.S. Geological Survey Geophysicist mailing

Box 25046 MS 973

Denver Colorado 80225 USA 303-236-3531 jmmeyer@usgs.gov FGDC Content Standard for Digital Geospatial Metadata FGDC-STD-001-1998