Measurements and Metrics of 'Fixed' Pattern Noise: A New Procedure for Thermal Camera Noise Measurement

In an ideal world, each camera pixel would exhibit the same behavior and response when stimulated with an incoming signal. In the real world however, variations between pixel's response (gain) and dark-current/extraneous-signal/etc. (offset) require a non-uniformity correction (NUC). The residual pixel to pixel variation following a NUC is the fixed pattern noise of the camera. For thermal cameras, the ability to NUC is critical, as the pixel's gain and offset typically change with temperature. Moreover, the offset typically drifts in time, even when the camera is at equilibrium. These additional dependencies of time and temperature make the "fixed" pattern noise not fixed, and make measurement agreement between laboratories much more difficult. In this work, we describe a modification of the standard thermal camera noise measurement procedure and analysis (at some specified equilibrium temperature) that removes the time dependencies of fixed pattern noise measurement. Additionally, we describe a temporal measurement to characterize the time dependent nature of "fixed" pattern noise. We show that this behavior is stationary, and independent on the direction of time since the NUC was defined. The temporal behavior is well described by a combination of power-law and liner time dependence. With this, new metric s can be considered to evaluation how frequent to conduct a NUC dependent on operational requirements.