The new generation PC-based array control electronics (PACE) system for emissive infrared projector real-time scene data processing has opened the potential for the development of more complex real-time nonuniformity correction (RNUC) algorithms than were formerly possible. In this paper, emitter array response data are analyzed in order to identify the underlying physical processes and to identify the form of the RNUC algorithm they suggest. It is shown that although the PACE system is capable of processing the algorithm, the development of a practical RNUC processor would seem to be limited by the complexities that underlie the observed variability in emitter response.
One proven technique for nonuniformity correction (NUC) of a resistor array infrared scene projector requires careful measurement of the output-versus-input response for every emitter in a large array. In previous papers, we have discussed methods and results for accomplishing the projector NUC. Two difficulties that may limit the NUC results are residual nonuniformity in the calibration sensor, and nonlinearity in the calibration sensor's response to scene radiance. These effects introduce errors in the measurement of the projector elements' output, which lead to residual nonuniformity. In this paper we describe a recent effort to mitigate both of these problems using a procedure that combines sensor nonuniformity correction and sensor calibration, detector by detector, so that these problems do not contaminate the projector NUC. By measuring a set of blackbody flood-field images at a dozen or so different temperatures, the individual detector output-versus-input radiance responses can be measured. Similar to the projector NUC, we use a curve-fitting routine to model the response of each detector. Using this set of response curves, a post-processing algorithm is used to correct and calibrate the images measured by the sensor. We have used this approach to reduce several sensor error sources by a factor of 10 to 100. The resulting processing is used to correct and calibrate all of the sensor images used to perform the projector NUC, as one step in the projector NUC. The procedure appears to be useful for any application where sensor nonuniformity or response nonlinearities are significant.
For many types of infrared scene projectors, differences in the outputs of individual elements are one source of error in projecting a desired radiance scene. This is particularly true of resistor-array based infrared projectors. Depending on the sensor and application, the desired response uniformity may prove difficult to achieve. The properties of the sensor used to measure the projector outputs critically affect the procedures that can be used for nonuniformity correction (NUC) of the projector, as well as the final accuracy achievable by the NUC. In this paper we present a description of recent efforts to perform NUC of an infrared projector under “adverse” circumstances. For example, the NUC sensor may have some undesirable properties, including: significant random noise, large residual response nonuniformity, temporal drift in bias or gain response, vibration, and bad pixels. We present a procedure for reliably determining the output versus input response of each individual emitter of a resistor array projector. This NUC procedure has been demonstrated in several projection systems at the Kinetic Kill Vehicle Hardware-In-the-Loop Simulator (KHILS) including those within the KHILS cryogenic chamber. The NUC procedure has proven to be generally robust to various sensor artifacts.
KEYWORDS: Nonuniformity corrections, Signal processing, Cameras, Infrared radiation, Projection systems, Thermography, Black bodies, Field effect transistors, Signal attenuation, Spatial frequencies
A new infrared projector emitter response curve-fitting procedure suitable for generating nonuniformity coefficients capable of being applied in existing real-time processing architectures is introduced. The procedure has been developed through detailed analysis of a Honeywell Multi-Spectral Scene Projector (MSSP) sparse array data set, combined with an appreciation of the underlying physical processes that lead to the generation of infrared radiance.
The concept for a new high spatial resolution, high-temperature, Dynamic Infrared Scene Projector (DISP) for generating high-speed (microsecond range) broadband (3-16 microns) IR scenery through visible pumping of DISP semiconductor scene (visible-to-infrared conversion) was developed, fabricated and tested. The principle of this new device operation and the results of our initial experimental study are reported for the first time. Key potential operating parameters of the new device prototype (based on a Germanium screen) are compared to that of modern conventional DISP engine (SBIR Emitter Array Projector).
In some of its infrared projection systems, the Kinetic Kill Vehicle Hardware-In-the-Loop Simulator (KHILS) facility uses two 512 x 512 Wideband Infrared Scene Projector (WISP) resistor arrays to stimulate two different camera wavebands at the same time. The images from the two arrays are combined with a dichroic beam combiner, allowing the two camera bands to be independently stimulated. In early tests it was observed that the projector bands were not completely independent. When one array was projecting, the projected pattern could be seen in the opposite camera band. This effect is caused by spectral “crosstalk” in the camera/projector system. The purpose of this study was to build a mathematical model of the crosstalk, validate the model with measurements of a 2-color projection system, and then use the model as a tool to determine the spectral characteristics of filters that would reduce the crosstalk. Measurements of the crosstalk were made in the KHILS 2-color projector with two different 2-color cameras. The KHILS Quantum Well Infrared Photodetector (QWIP) Mid-Wave (MW)/Long-Wave (LW) camera and the Army Research Laboratory HgCdTe (HCT) MW/LW camera were used in the tests. The model was used to analyze the measurements, thus validating the model at the same time. The model was then used to describe conceptual designs of new 2-color projection configurations, enabling a prediction of crosstalk in the system, and selection of filters that would eliminate the crosstalk.
The concept for a new high spatial resolution, high-temperature, Dynamic Infrared Scene Projector (DISP) for generating high-speed (microsecond range) broadband (3-16 microns) IR scenery through visible pumping of DISP semiconductor scene (visible-to-infrared conversion) was developed, fabricated and tested. The principle of this new device operation and the results of our initial experimental study are reported for the first time. Key potential operating parameters of the new device prototype (based on a Germanium screen) are compared to that of modern conventional DISP engine (SBIR Emitter Array Projector).
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