Analysis of Tipping-Curve Acceptance Criteria for Ground-Based Radiometer Calibration

The tipping-curve method is widely used to provide the cold calibration point for calibration of ground-based radiometers. Statistical analysis of the opacity air mass pairs have been used as measures of the tip curve quality, but the choice of acceptance criteria has been subjective. An analysis of the tipping curve acceptance criteria was accomplished by simulation of a total power radiometer under non stratified conditions due to perturbations of water vapor content. Relationships between the root mean square error (RMSE) in zenith brightness temperature and regression coefficient were examined. While the RMSE decreased with increasing regression coefficient, a stringent acceptance criteria did not ensure accuracy likely due to the presence of net horizontal gradients. On the other hand, for radiometers with multiple channels the standard deviation of brightness temperature measurements of a reference black body, also known as spectral consistency, was found to be a robust indicator of calibration accuracy.