Determining stabilization accuracies of vibrationally excited FPA cameras by frame-to-frame measurements of MTF-values

摘要

A new method for obtaining the geometric resolution of infrared cameras with focal plane array (FPA) detectors is introduced. Selected values of the modulation transfer function (MTF) are measured in real time on a frame-to-frame basis. For this purpose a test bar pattern is imaged onto the FPA plane so that the bar image has a spatial frequency which is detuned with respect to the FPA Nyquist frequency. This generates a beat signal whose amplitude corresponds to the contrast of the bar image to be measured, without the sampling MTF. If the test bar pattern covers a range of at least half a beat period the modulation amplitude can be determined independent of the actual phase position. This method can be adapted to real-time MTF measurements. Examples are presented for shaker excitations of an IR camera on a platform with means for active and passive stabilization. Sweeping the frequency in sinusoidal excitation mode exhibits resonance structures deteriorating the camera resolution thus giving valuable information for optimizing the design of camera and suspension system. Residual stabilization errors are measured under random vibration excitations for each individual frame, their distribution being conveniantly visualized by bar histograms.