Measuring the MTF of undersampled staring IRFPA sensors using 2D discrete Fourier transform

Mark A. Chambliss; James A. Dawson; Eric J. Borg

doi:10.1117/12.210058

22 May 1995 Measuring the MTF of undersampled staring IRFPA sensors using 2D discrete Fourier transform

Mark A. Chambliss, James A. Dawson, Eric J. Borg

Proceedings Volume 2470, Infrared Imaging Systems: Design, Analysis, Modeling, and Testing VI; (1995) https://doi.org/10.1117/12.210058
Event: SPIE's 1995 Symposium on OE/Aerospace Sensing and Dual Use Photonics, 1995, Orlando, FL, United States

Abstract

Accurate measurement of the modulation transfer function (MTF) for imaging systems can be obtained by viewing a known target that is broad-band in the Fourier domain. A slit target is frequently used; however, undersampled staring systems cannot properly reproduce this type of target since frequencies above Nyquist are folded into those below Nyquist, resulting in the well known aliasing effect. Proper accounting of aliasing is needed to determine the true system response to frequencies below Nyquist. To alleviate the aliasing problem, existing methods use various techniques that effectively increase the sampling rate across the slit. These methods usually require some type of positioning device in order to accurately control the relation of the location of the slit with respect to the sensor array. This paper provides an alterative method in which a marginally resolved slit is canted with respect to the sensor array. MTF values can be determined at any slit cant angle greatly simplifying the laboratory procedures and requirements. The two-dimensional (2-D) discrete fast Fourier transform (FFT) of the canted-slit image enables separation of the aliased and non-aliased signal components. This allows the accurate determination of MTF for frequencies both above and below system Nyquist. Temporal averaging and reference image substraction are used to reduce the effects of system noise on the measurements. MTF values determined using this method are compared to calculated, idealized predictions for three undersampled medium- wave infrared (IR) systems. This comparison provides the validation of this procedure and demonstrates its general utility. The general improvement offered in measuring MTF for aliased systems is presented in terms of limiting accuracy.

Citation Download Citation

Mark A. Chambliss, James A. Dawson, and Eric J. Borg "Measuring the MTF of undersampled staring IRFPA sensors using 2D discrete Fourier transform", Proc. SPIE 2470, Infrared Imaging Systems: Design, Analysis, Modeling, and Testing VI, (22 May 1995); https://doi.org/10.1117/12.210058

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