Scientists and engineers from the U.S. Geological Survey (USGS) Earth Resources Observation and Science Center (EROS) Cal/Val Center of Excellence (ECCOE) collected in situ measurements using field spectrometers to support the validation of surface reflectance products derived from Earth observing remote sensing imagery. Data provided in this data release were collected during selected Earth observing satellite overpasses and tests during the months of May through November 2021. These data were collected at six field sites during 2021. These field sites included South Dakota State University (SDSU) Research Park in Brookings, SD, near the Brookings Airport in Brookings, SD, a private land holding in Sanborn County, SD, Edwards Air Force Base in CA, Bureau of Land Management (BLM) managed land near Moneta, WY, State of Oklahoma Commissioners of the Land Office managed land near Guymon, OK, and Coconino National Forest near Flagstaff, AZ. Each field collection file includes the calculated surface reflectance of each wavelength collected by the spectroradiometer. Initial data collection methodology relied upon a single field spectrometer. Field collections conducted after 25 August 2021 contain data from two spectrometers. The addition of the second spectrometer reduced uncertainty in the field measurements by accounting for changes in solar irradiance. The differing methodologies are denoted as "Single Spectrometer" and "Dual Spectrometer". Field spectrometer data are provided as Comma Separated Values (CSV) files and GeoPackage files. Lastly, data were collected during the Big Multi-Agency Collection round robin and are provided for all targets observed during the campaign.