Measurement method of the modulation transfer function of focal plane arrays

Focal plane arrays (FPA) of HgCdTe detectors with responses in the 3-5micrometers or 8-14micrometers bands have been successfully incorporated into infrared imagers. Using a variety of digital signal processing techniques, good imagery has been obtained but the image quality is limited by sampling effects at the focal plane that cause non-isoplanantism and aliasing. The verification of the operation of these detectors is an important step in the design and development process. Modulation transfer function (MTF) is a measurement of how well the system will faithfully reproduce the scene. As the MTF decreases, scene detail associated with those specific spatial frequencies will be reproduced with lower contrast. The development of focal plane arrays with considerable on-chip processing, notably time-delay integration, imposes new and severe requirements on the instrumentation to establish the MTF of the integrated focal plane arrays.1 This paper details a method for measuring the MTF for such arrays. Several methods to derive the MTF from the experimental data were investigated; the preferred approach is presented.