Spectral reflectance data of rock and soil in southcentral Alaska

An ASD FieldSpec 4 Hi-Res NG Spectroradiometer was used to collect the reflectance properties of soil and rock in southcentral Alaska, USA (Figure 1) around the city of Anchorage (Figure 2) and the Prince William Sound (Figure 3). Reflectance is a property of the material being observed, being the ratio of the amount of light leaving a target to the amount of light striking the target. Reflectance is a unitless value from 0 to 1, where a value of 0 indicates that the material absorbs all energy and 1 indicates total reflectance. Additionally, samples were collected from the field and later measured using the spectrometer in the laboratory. Both field and laboratory data were collected in the summer and fall of 2022.
 
The ASD FieldSpec 4 Hi-Res NG is a point spectrometer that has a spectral range of 350 to 2500 nm, covering the visible and near-infrared (VNIR) and short-wave infrared (SWIR) portions of the electromagnetic spectrum. The spectral resolution is 3 nm at 700 nm and 6 nm at 1400 and 2100 nm, and the spectral sampling (bandwidth) is 1.4 nm at 700 nm and 1.1 nm at 1400 and 2100nm. The instrument collects 2151 channels of spectral data within a 25° field of view (Malvern Panalytical, 2023).
 
In sunny conditions, measurements were collected in the field on areas ranging between 1 – 3 m2 using the bare fiber optic cable with a 25° field of view and sunlight. When materials are measured using sunlight, reflectance values can be greater than 1 and less than 0 due to atmospheric artefacts (e.g., Kokaly et al., 2021). In cloudy conditions, measurements were collected in the field using a contact probe with a 10 mm spot size that uses artificial light provided by a halogen bulb. Lab measurements were all collected using the contact probe, and if the samples were rock, measurements were collected on both the external part of the sample and on a saw-cut face (sample interior) and reported as different entries. Ten measurements were collected for each entry, during which the probe or cable was moved to capture different surfaces of the sample to assure all representative features were measured. The ten spectra measurements were averaged, after which a splice correction was applied using the ASD ViewSpec Pro software that corrects steps in the data due to inherent variations in detector temperature sensitivity (Milton et al., 2009).  
 
The files provided in this data release are as follows:
 
Figure 1 (“overview map.jpg”) is an overview map of the field locations in Anchorage and the Prince William Sound, outlined with black rectangles.
 
Figure 2 (“Anchorage samples.jpg”) is a map of the Anchorage field area showing locations of field measurements (marked with a blue square) and where samples were collected from the field and later measured in the laboratory (marked with a purple circle). Numbers correspond to the numeric value in the SampleID column in “Alaska_SampleLocationsandDescriptions.txt”
 
Figure 3 (“PWS samples.jpg”) is a map of the Prince William Sound field area showing locations of field measurements (marked with a blue square) and where samples were collected from the field and later measured in the laboratory (marked with a purple circle). Numbers correspond to the numeric value in the SampleID column in “Alaska_SampleLocationsandDescriptions.txt”
 
“Metadata.xml” is the metadata for the data release.
 
“Alaska_DataDictionary.txt” is a tab delimited text file that contains descriptions of the names and definitions for each attribute.
 
“Alaska_SampleLocationsandDescriptions.txt” is a tab delimited text file that provides details of the samples and sample locations.
 
“Alaska_SpectraData.txt” is a tab delimited text file that contains the averaged and splice corrected spectral reflectance data (unitless) for each of the samples listed in “Alaska_SampleLocationsandDescriptions.txt”
 
Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
 
References Cited
Kokaly, R.F., Swayze, G.A., Livo, K.E., Hoefen, T.M., Hubbard, B.E., Meyer, J.M., Cox, E.M. and Gnesda, W.R., 2021, Imaging spectroscopy applied to mineral mapping over large areas: Impact of residual atmospheric artefacts in reflectance spectra on mineral identification and mapping. In: 2021 IEEE International Geoscience and Remote Sensing Symposium IGARSS (p. 1855-1858). IEEE.
 
Malvern Panalytical, 2023, ASD FieldSpec 4 Hi-Res NG Spectroradiometer, accessed 27 January 2023 at https://www.malvernpanalytical.com/en/support/product-support/asd-range…
 
Milton, E. J., Schaepman, M. E., Anderson, K., Kneubühler, M., & Fox, N. (2009). Progress in field spectroscopy. Remote Sensing of Environment, 113, S92-S109. https://doi.org/10.1016/j.rse.2007.08.001