Calibration of night vision goggles: an SI-units-based gain measurement technique.

A gain measurement technique for the calibration of night vision goggles (NVG) is proposed and evaluated. This technique is based on the radiance measurements at the input and output of the NVG. In contrast to the old definition, which uses a non-International System of Units (SI) traceable luminance, the "equivalent luminance unit," the suggested technique utilizes the radiance quantities that are traceable to the SI units through National Institute of Standards and Technology (NIST) standards. Due to the implementation of the scaling coefficients originating from the NVG spectral responsivities, the same NVG gain is expected within both techniques. The suggested method was evaluated at the NIST night vision calibration facility and the experimental data were compared to the results obtained with a commercial NVG test set. The comparison of the radiometric quantities obtained using the two different methods indicated differences up to 15% due to different calibration conditions. However, at proper calibration, equal NVG gains within both the suggested and old gain definitions were measured for the goggles equipped with a filmless image tube. The NVG gain uncertainty analysis, including the effect of no-moon night sky radiation, was performed for goggle types A, B, and C.