Engineering perspectives related to specification, design, manufacture and evaluation of collimator lenses are discussed using the example of a recently manufactured collimator for use in thermal imager evaluations. Collimator optics are important test facility components used for the evaluation of thermal imager systems. The thermal imager test facility at NVESD needed new collimator lenses in order to use targets small enough to work within the limitations of blackbody uniformity while testing thermal imager systems for the Driver's Viewer Enhancer program. These systems require very low spatial frequency targets to completely characterize minimum resolvable temperature difference. Three perspectives on the design, manufacture and testing of a collimator lens assembly are presented in this paper: (1) the perspective of the user, who is the optics specifier; (2) that of the optics designer/manufacturer; and (3) that of the optical testing engineers who validated the optics design using CODE V and tested the optics at NVESD's optical test facility. Different perspective result in the customary use of different parameters to define specifications. Therefore, optics specifiers must consider various perspectives to ensure the lens design meets desired requirements.
Proc. SPIE. 2470, Infrared Imaging Systems: Design, Analysis, Modeling, and Testing VI
KEYWORDS: Staring arrays, Nonuniformity corrections, Thermography, Imaging systems, Sensors, Calibration, Control systems, Black bodies, Minimum resolvable temperature difference, Temperature metrology
Blackbody thermal reference sources are critical test facility components used for the evaluation of thermal imager systems. Extended source blackbodies are used at the Night Vision and Electronic Sensors Directorate (NVESD) for testing and evaluation of new generations of thermal imagers. Wider field of view and more sensitive systems especially require knowledge of the accuracy, stability, and uniformity of the thermal reference sources used for their evaluation. This paper demonstrates measurement techniques used to evaluate extended source blackbodies and their controllers using a sensitive, stable, and uniform thermal imager, the Amber Radiance 1.
The noise equivalent temperature difference (NETD) of forward looking infrared (FLIR) systems is a widely used performance parameter that characterizes the sensitivity of thermal imaging sensors. Although this parameter has been used for many years, there has always been some confusion and misunderstanding about how to measure it. Differences in opinion on how this measurement should be made can cause substantial variations in reported values of NETD measurements. It is the intent of this paper to clearly describe the measurement technique used at Night Vision and Electronic Sensors Directorate (NVESD).
Measurement of the Optical Transfer Function (OTF) of discretely sampled thermal imaging systems, e.g. parallel scanned FLIR systems, on which analysis is done in the cross scan direction, and staring focal plane arrays, it increasingly important as digital image acquisition device technology for the 3 - 5 and 8 - 12 micron (infrared) spectral regions is maturing. The traditional measurement methods used for continuous scan systems may not be valid for discretely sampled systems. This paper presents results of measurements of the OTF using a translating slit to obtain the Line Spread Function (LSF) for discretely sampled systems. Multiple frame acquisition is used for removal of temporal and fixed pattern noise. It is the intent of this laboratory effort to develop a measurement technique to be used when collecting OTF data for discretely sampled systems. The new measurement technique is potentially suitable for all systems, and if successful, will permit characterization of vertical system MTF. If this measurement method is found to be useful, it will be used to generate the OTF data used in the NVEOD FLIR92 model for further development and verification of the model.