Measurement of the nonuniformity of first responder thermal imaging cameras

Police, firefighters, and emergency medical personnel are examples of first responders that are utilizing thermal imaging cameras in a very practical way every day. However, few performance metrics have been developed to assist first responders in evaluating the performance of thermal imaging technology. This paper describes one possible metric for evaluating the nonuniformity of thermal imaging cameras. Several commercially available uncooled focal plane array cameras were examined. Because of proprietary property issues, each camera was considered a 'black box'. In these experiments, an extended area black body (18 cm square) was placed very close to the objective lens of the thermal imaging camera. The resultant video output from the camera was digitized at a resolution of 640x480 pixels and a grayscale depth of 10 bits. The nonuniformity was calculated using the standard deviation of the digitized image pixel intensities divided by the mean of those pixel intensities. This procedure was repeated for each camera at several blackbody temperatures in the range from 30° C to 260° C. It has observed that the nonuniformity initially increases with temperature, then asymptotically approaches a maximum value. Nonuniformity is also applied to the calculation of Spatial Frequency Response as well providing a noise floor. The testing procedures described herein are being developed as part of a suite of tests to be incorporated into a performance standard covering thermal imaging cameras for first responders.