Vicarious calibration approaches using in-situ measurements is a key technique applied to on-orbit remote sensors. The in-situ measurements have advantages in terms of traceability and quantifiable accuracy making them ideal for interconsistency studies of on-orbit sensors. The Committee on Earth Observation Satellites (CEOS) Working Group on Calibration and Validation (WGCV) Infrared Visible Optical Sensors (IVOS) initiated the Radiometric Calibration Network (RadCalNet) to provide automated surface and top-of atmosphere reflectance data from multiple participating ground sites to the world-wide user community. RadCalNet standardizes protocols for collecting data, processing to top-of- atmosphere reflectance, and provides SI-traceable uncertainty budgets for the 4 currently operating sites. RadCalNet data from the Railroad Valley Playa, Nevada site was used to provide an SI-traceable, absolute radiometric calibration of the Enhanced MODIS Airborne Simulator (eMAS) as part of an overflight of opportunity during the FIREX-AQ campaign. The results shown here demonstrate the utility of RadCalNet data for absolute radiometric calibration of airborne imagers making flights of opportunity without the need for coordination with a field validation team.