The Remote Sensing Group (RSG) at the University of Arizona performs the vicarious calibration of airborne and spaceborne sensors using ground-based measurements. Vicarious calibration is important because it is independent of the sensor and any onboard calibration system, but it requires that RSG personnel be present at a test site during the aircraft or satellite overpass. The ground-based data collection can be limited by poor weather, and also by the large travel distances from RSG's laboratory to the test sites.This dissertation presents an automated methodology that is used in support of vicarious calibration. The most important parameter measured during a vicarious calibration field campaign is the surface reflectance, and this work describes the method and instrumentation to obtain surface reflectance in the absence of RSG personnel. The instrumentation required to measure the surface and atmospheric parameters is discussed. The design and laboratory characterization of a nadir-viewing, multispectral radiometer is presented. Finally, results using this methodology are compared to those obtained using vicarious calibration, and also with the top-of-atmosphere radiance for one Terra MODIS, and two Aqua MODIS overpasses.