Calibration is critical for useful long-term data records, as well as independent data quality control. However, in the context of Earth observation sensors, post-launch calibration and the associated quality assurance perspective are far from operational. This paper explores the possibility of establishing a global instrumented and automated network of test sites (GIANTS) for post-launch radiometric calibration of Earth observation sensors. It is proposed that a small number of well-instrumented benchmark test sites and data sets for calibration be supported. A core set of sensors, measurements, and protocols would be standardized across all participating test sites and the measurement data sets would undergo identical processing at a central secretariat. The network would provide calibration information to supplement or substitute for on-board calibration, would reduce the effort required by individual agencies, and would provide consistency for cross-platform studies. Central to the GIANTS concept is the use of automation, communication, coordination, visibility, and education, all of which can be facilitated by greater use of advanced in-situ sensor and telecommunication technologies. The goal is to help ensure that the resources devoted to remote sensing calibration benefit the intended user community and facilitate the development of new calibration methodologies (research and development) and future specialists (education and training).