## 3 Materials and Methods  
Figure 1 shows the study area for this analysis in northern and central California, USA. This region was chosen because of the confluence of data availability from the recently opened AVIRIS hyperspectral image archive ([[https://aviris.jpl.nasa.gov/alt_locator/](https://aviris.jpl.nasa.gov/alt_locator/)]([https://aviris.jpl.nasa.gov/alt_locator/](https://aviris.jpl.nasa.gov/alt_locator/))) and high-quality soil maps maintained by the UC Davis California Soil Resource Lab ([[https://casoilresource.lawr.ucdavis.edu/](https://casoilresource.lawr.ucdavis.edu/)]([https://casoilresource.lawr.ucdavis.edu/](https://casoilresource.lawr.ucdavis.edu/))). The study area spans an unusually wide range of soil orders, textures, and chemical properties. A diversity of soil provenances is also present as a result of the geologic diversity of the region. Six of the nine soil orders in California are sampled in this study. Five AVIRIS flight lines were selected for use in this analysis on the basis of pedologic and spectral diversity (Figure 2). Critically, all five flight lines were acquired on the same day as coincident Landsat 8 acquisitions, allowing for a direct comparison of the effect of spectral resolution on dimensionality, as well as the opportunity for a direct comparison of AVIRIS and Landsat standard surface reflectance products. A diversity of agricultural and natural vegetation, settlements, bare soils, and water is present in the dataset. Some geological diversity is present in crystalline basement and sedimentary rock outcrops within the Sierra and Coast Range flight lines. Wetlands are present in the San Francisco Bay-Delta, as well as the San Joaquin River National Wildlife Refuge. All AVIRIS images were downloaded as Level 2 Atmospherically Corrected Reflectance from the AVIRIS Data Portal at [[https://aviris.jpl.nasa.gov/alt_locator](https://aviris.jpl.nasa.gov/alt_locator)]([https://aviris.jpl.nasa.gov/alt_locator](https://aviris.jpl.nasa.gov/alt_locator)). Coincident Landsat 8 LaSRC modeled surface reflectance products were downloaded from the USGS at [[https://earthexplorer.usgs.gov](https://earthexplorer.usgs.gov)]([https://earthexplorer.usgs.gov](https://earthexplorer.usgs.gov)). Figure 1: Northern California AVIRIS flight lines used in this analysis. Five lines were selected from the AVIRIS classic data archive on the basis of pedologic and agricultural diversity. Landsat 8 acquisitions were collected on the same day as each of the five flight lines. Simplified maps showing soil orders (right), as well as lithologic provenance (inset, upper right), and cation exchange capacity (inset, lower left) illustrates the complexity of soil properties in the study area. Six of the nine soil orders are represented in these flight lines. Soil maps from the UC Davis California Soil Resource Lab ([[https://casoilresource.lawr.ucdavis.edu/](https://casoilresource.lawr.ucdavis.edu/)]([https://casoilresource.lawr.ucdavis.edu/](https://casoilresource.lawr.ucdavis.edu/))). Map data © 2017 Google INEGI. Figure 3 shows a comparison of sensor resolutions for Landsat 8 OLI and AVIRIS, as well as the older Landsat 7 ETM+ and newer Sentinel 2 MSI sensors. The AVIRIS sensor images the Earth in 224 channels over the full VSWIR 365 to 2500 nm spectral range at a 10 nm spectral resolution. In comparison, multispectral sensors such as Landsat and Sentinel 2 collect a much smaller number of spectral bands with much wider bandpasses. As of the date of publication of [1], the signal-to-noise ratio (SNR) of AVIRIS was approximately 1000 for the VNIR, 700 for SWIR1, and 250 for SWIR2. In contrast, the Landsat 8 OLI SNR ranges between 201 and 367 for the bands used in this study [42]. AVIRIS oversamples most features in the reflectance spectrum and is therefore also able to resolve physical parameters about spectral slope and narrow band absorptions which are averaged together by OLI. Figure 3: Spectral band comparison for Landsat 7/8, Sentinel 2, and AVIRIS.