The design of a State-of the-Art Infrared Sensor requires a number of diverse disciplines. Without proper programmatic controls, the attendant subsystem design studies can result in the imposition of incompatible requirements on the overall sensor design. One approach for assuring the orderly development of a sensor design is the use of a Sensor Specification which reduces the top level system requirements into a set of self-consistent subsystem requirements. A methodology for generating such a specification is described in this paper. Emphasis is placed on sensors designed for Ballistic Missile Defense (BMD) applications; however, a similar approach can be utilized for any infrared system.

There is substantial research evidence which indicates that data in the short wave infrared (SWIR) spectral region will greatly improve the information content of remotely sensed data. Bands are required in the 1.55-1.75 μm and 2.08-2.35μm spectral regions for a variety of agricultural and geological investigations. It is anticipated that future Landsat sensors will use pushbroom linear array technology in order to obtain high resolution, improved sensitivity and increased system reliability. To obtain early laboratory and field data, an airborne pushbroom image system has been designed for operation in the short wave infrared spectral region. The system uses a 64-element staggered PbS array and is operated at 195°K. The instrument has been designed to operate in an aircraft and will view an 19 degree swath width with a 5.8 mrad IFOV. The spectral bandwidth of each channel is .05 μm and a NE ▵p in the order of .2% is provided. The requirements for more advanced detector arrays for use in future NASA spacecraft remote sensing instruments are also discussed.

Thermography has been available for some time as an aid in the determination of temperature differentials. Burton, et al, have demonstrated that thermographic techniques may be used qualitatively to detect induced surface currents resulting from impinging Electromagnetic (EM) waves on particular shapes. The surface currents are detectable because of the energy deposited on the object in the form of I²R heating. A knowledge of the induced surface currents is invaluable to the study of radar cross section reduction and Electromagnetic Pulse (EMP) absorption. Therefore, a method is presented which provides a method of determining the temperature distribution on a complex shape subjected to microwave radiation. Thermographic detectors are either energy detectors (thermocouples) or photon detectors (semiconductors). A model is developed for each type which describes the infrared emission detection associated with a complex shape.

A. number of new optical ceramics have been synthesized and characterized for potential application to advanced missile sensor windows. The new materials have been selected to have dual mode capability with an optical cut-off beyond 5μm, and properties conducive to thermal shock and rain erosion resistance. Among the new materials which have significant potential are silicon mullite, its analogue germanium mullite, zinc alumino-germanate glass ceramic, aluminum nitride, toughened zirconia and calcium lanthanum sulfide for long wave IR applications. These materials are all in the developmental stages and advancements in the synthesis processes are needed before they meet all the requirements of advanced sensor windows. However, considerable optical, electrical, mechanical and thermo physical data has been accumulated and is presented in this paper, and the new materials are potentially capable of meeting the needs of the advanced missile systems. In addition, these advanced optical ceramics when fully developed, are expected to prove advantageous in a variety of land, sea, air and space applications.

Teledyne Brown Engineering has developed a low-cost infrared seeker (LCIRS) for manportable terminal homing rounds. In order to minimize production costs, the development emphasized design simplicity and inexpensive manufacturing processes. LCIRS engagement parameters represent a short-range round launched over a land combat vehicle. The seeker optical system has an aerodynamically spun dome that holds a roof mirror on the inside cylindrical axis. This provides a rotary field scan for a strapdown primary aspheric mirror and detector array. The two-color thermoelectrically cooled array uses lead sulfide and lead selenide detector elements. A coated germanium anti-solar spectral filter with a passband that cuts on at 2.3 μm is employed. Replicated optics were used to minimize costs. Considerable attention was devoted to the design of signal processing electronics for the LCIRS. Multichannel preamplifiers were employed. Complete signal processing electronics were developed, fabricated, and tested. Design requirements, design parameters, optical system characteristics, and system performance are presented.

Optimal use of a calibrated infrared imaging radiometer for target signature studies requires rapid analysis and reduction of the output imagery. A minicomputer based digital image processing system is described. Operations such as level slicing, integration of radiant intensities, and image addition are performed digitally in an interactive manner with the system user. An application of this system for the production of simulated infrared targets is presented. The simulated targets consist of transparencies or masks which are back illuminated by an infrared source. A technique somewhat similar to a halftone process is used to encode the pixel intensities onto the masks. The illumination system design and mask fabrication process are described.

It is frequently desired to measure the flux exiting from a small aperture, using a radiometer that must be positioned near to that source. Such conditions arise, for instance, in determining the absolute output of a spectrometer or in measuring the throughput of an optical device. Since most radiometers are designed to have the sensor located in the focal plane of the fore-optics, a portion of the radiation collected under these circumstances will not fall onto the detector. This situation is considered here to indicate the relationship of the flux discerned to the radiance of the object as a function of the object distance involved. Accurate measurements of the radiance of nearby objects is a far more complex procedure than is that of distant objects. Those conditions for attaining the more accurate measurements are described.

The angular measurement uncertainty of an infrared (IR) sensor has been determined for expected signal waveforms and associated data processing algorithms. The problem was formulated by using the visibility factor and calculating its interaction with the characteristics of the leading edge (LE) and peak detection (PD) processing algorithms. Functional forms of the measurement uncertainty for both the scan and cross-scan directions are presented using rectangular and Gaussian signal waveforms. The relative merits of the LE and PD algorithms are discussed, and the measurement variations between rectangular and Gaussian input signal waveforms are compared.

The radiometric quality of the measurement data is key to the Homing Overlay Experiment (HOE) system functional performance and the tactical system performance implications. The terminology adopted by the HOE program to specify sensor requirements that will insure the adequacy of the radiometric measurement data is presented in this paper.

Applicable concepts in sampling statistics are introduced and applied to establish calibration measurement requirements based on sensor performance requirements and sensor measurement characteristics. The sampling statistics included allow the determination of the number of conditions and samples at each condition necessary to meet a specified uncertainty with a given confidence interval. The effect of correlation between parameters in sampling requirement reduction is treated. These analyses are then used to determine data processing loads, data storage requirements and facility operation time required to meet specified levels of system performance.

A Honeywell Level-6 minicomputer has been adapted to the task of conducting the test and calibration of the HOE Homing Sensor at the Honeywell Electro-Optics Center's Low Background Calibration Facility, (LBCF). Special circuitry has been added to the standard Level-6 General Purpose Interface units to enable the computer to communicate with the sensor and the LBCF. Communication is accomplished by a handshake technique controlled by assembly language interrupt programs. These programs are subroutines in larger FORTRAN programs which implement specific test procedures. One group of FORTRAN test programs verify the proper functioning of the sensor and run relatively autonomously. A second group, on the other hand, for the more complete LBCF tests, are designed to be highly interactive, providing the test conductor the means to readily select test parameters as desired.

Two new methods of bandwidth normalization using root mean square (RMS) techniques are described. Comparison is made with conventional techniques using several typical sources and detectors. Methods of placement of the passband are also discussed. A simple RMS technique yields results with approximately 30% less error than conventional peak normalization, while a more complex iterative process yields results with even lower errors. Implementation of these methods is indicated when the spectral radiance of either the source or the detector is unknown.

Extrinsic LWIR detectors exhibit departures from a "normal" linear response (irregularities). In the early 1970's, observations of these phenomena were inconsistent and unrepeatable, and the phenomena were not explainable by existing physical theory, so many observers labeled the phenomena "anomalous." Recent investigations into detector theory, processing, and application have shown repeatability and revealed apparent connections between various irregular aspects of detector response, and have indicated means of mitigating the irregularities' effects. Herein, extrinsic silicon detector irregularities generally recognized by the LWIR detector community are described with illustrations drawn from the literature. Pertinent discussions from the recent Extrinsic Detector Behavior Conference are summarized. The Army/Air Force program for mitigating the irregularity problem is outlined.

Wideband longwave infrared (LWIR) attenuators used in calibration sources can introduce subtle changes in the spectrum of the test beam. As a result, there are probably no sensor calibration sources that have unimpeachable spectral purity at all levels. This paper reviews several of the mechanisms that can alter the spectrum of the test beam, discusses measures that can reduce spectral coloration and describes spectroradiometer configurations that can be used for in situ characterization of the test beam.

The Advanced Sensor Evaluation and Test (ASET) Facility is a system for the calibration and exercise of infrared sensors under conditions simulating those of outer space. Sensors typically consist of a telescope, detector focal plane array, electronics, and data processing equipment. They normally detect radiation from distant, unresolved objects in the 4 μm to 30 μm wavelength region. Accordingly, the ASET facility comprises two radiant sources, collimating optics to place the sources at infinity, scanning mirrors to permit two-axis control of the test beam, a radiation monitor, and associated control and computer interface equipment. The radiant incidance range over which the sensors normally operate precludes the use of an unattenuated blackbody source. The ASET sources use blackbody emitters in conjunction with various attenuators which are difficult to characterize theoretically. Therefore, an experimental calibration of the facility was performed to determine the spectral radiant incidance in the test beams. The techniques employed for and the results of this calibration are reported here.

Since the initial 1970 operation of the ASET Facility, the internal calibration monitor bolometer responsivity has been determined by three optical and one electronic means yielding differing results ranging from 6.51 x 10⁴ V/W to 22.8 x 10⁴ V/W. During the HOST sensor calibrations in the ASET and POST facilities it was found that one of the optical methods yielded HOST NEFD's compatible with the POST results. This same responsivity is currently being employed in the DOT/ASET sensor calibrations and resulted in reasonable agreement between DOT sensor Flight lA and ground based stellar measurements. It is shown here that by recalculation with ASET bolometer test data it is possible to bring the results of the electronic and two of the optical methods into agreement with the respon-sivity used for HOST and DOT, and that this value also eliminates the longstanding factor of 2.8 discrepancy between the ASET and ARC-7V measurements of the SRS sensor NEFD. It is pointed out that while this bolometer responsivity determination does not clear up the discrepancy of the ASET and BONT calibrations of the FAIR II TAB sensor, it does signifi-cantly increase consistency of the ASET facility internal calibrations as well as bring the ASET, POST and ARC-7V facilities into accord.

The general design features of a new low-background infrared sensor test facility which is being installed at Lockheed Missiles & Space Company, Inc. are described. A brief description of the following is given: the facility layout, clean room facility, vacuum chamber, cryo shroud, cryo/vacuum system, optical system, optical control system, infrared sources, and sensors, overall system control and instrumentation.