Calibration of Microwave Reference Blackbodies and Targets for Use in Satellite Observations: An Analysis of Errors in Theoretical Outlooks and Testing Procedures

Microwave reference blackbodies and targets play a key role in astrophysical and geophysical studies. The emissivity of these devices is usually inferred from return-loss experiments which may introduce at least 10 separate types of calibration errors. The origin of these inaccuracies depends on test conditions and on the nature of each target. The most overlooked errors are related to the geometry adapted in constructing reference loads and to the effects of conduction or convection. Target shape and design can create an imbalance in the probabilities of absorption and emission. This leads to loss of radiative equilibrium, despite the presence of a thermodynamic steady state. Heat losses or gains, through conduction and convection, compensate for this unexpected physical condition. The improper calibration of blackbodies and targets has implications, not only in global climate monitoring, but also relative to evaluating the microwave background.