Spectral measurement instrumentation for the study of absolute radiance and contrast in the 1.5 to 13 micrometer region has been fabricated. Measurement technology has been developed based on fifteen years of experience. Spectral measurement instrumentation and techniques are discussed, including calibration methods, data acquisition and data reduction. Examples of recent natural background spectra are presented in both absolute and contrast forms.
Transmission and meteorological measurements are taken at both ends of a double-ended overwater transmission path. Three radiometer heads are used in connection with visible and blackbody sources to cover the visible, near, mid-, and far infrared spectrum. Measurement of the meteorological parameters of wind speed and direction, temperature, dew point, pressure and precipitation is accomplished from instrumented towers located adjacent to the source and the receiver sites.
The effects of the atmosphere on electro optic (E0)system performance should be included in the development cycle. Experience with other systems and predicted variability in the atmosphere should be considered in design. Expected atmospheric effects should be included in the test requirements and validated. San Nicolas Island has been selected as the tri service marine test site for EO systems. Instrumentation for measuring meteorological parameters and multi-band transmission measurements during system test is now operational and available for EO system test.
The purpose of the Navy-Wide Optical Signatures Program is to provide target signature, clutter background, and atmospheric data to Navy electro-optical programs (excluding laser systems). While the visible and ultraviolet spectral regions areincluded within the scope of this task, primary emphasis has been upon providing data for the infrared spectral region. The purpose of this paper is to discuss measurements, analysis, and simulation tasks which are being performed to provide an understanding of target/background/infrared system inter-relationships. Measurement tasks include air-to-air, air-to-ground, and ground-to-air operations with a variety of targets and background scenes using the following equipment: a. Airborne multispectral scanner, b. Radiometric imaging FLIR, c. Airborne measurement pod in conjunction with an AIM-9L seeker, and d. A variety of interferometers and infrared search sets. Analysis tasks include: a. Statistical analysis and modelling of background scenes, b. Spectral extrapolation, and c. Evaluation of simulation methods. Simulation tasks include: a. Development of an AIM-9L optics and reticle simulation, b. Development of fast storage/recall techniques for the background/reticle ensemble, c. Signal processing simulation and hardware interface, d. Multi-detector system simulation, and e. Validation. Each of the elements above is discussed in some detail with emphasis on the manner in which each relates to the overall task.
Field tests of low IR-reflecting paints designed to reduce aircraft IR signatures are being conducted at the Naval Weapons Center. The relative effectiveness of these paints is determined by making ground-static solar reflectance measurements from large-scale models that have been painted with the candidate IR paints. A comparison is made between the low IR-reflecting paints and the standard paints to determine the amount of reduction in IR skin signature. A documentary film ( 8 min.) depicting the Scale Model Aircraft Reflectance Testing program (SMART) will be shown.
The intent of this paper is to provide a comprehensive overview of the optical factors which affect system choice in 1011 imaging applications. Illustrative design alternatives are developed and discussed. Single element designs, refractors, reflectors, and catadioptric designs are described and compared. Diffraction-limited performance is explained and predictions made of real-world performance. Production tolerances, and a method for predicting degradations experienced in mass production are presented. Radiometric aspects are left for subsequent papers.
This paper is an analytical study of the scan noise in image scanning systems and its effects upon the sensor. The specific source of scan noise to be considered is that generated by the detectors as they pass over the diffraction pattern of an off-axis source. The supports of a Cassegrain optical system are the diffracting apertures of concern in the present study. Two types of support structures will be compared for their applicability to system trade-offs. In addition, the three principal types of scan noise are classified according to their effects upon the signal processing. The relative importance of each noise type if analyzed, in detail, from the standpoint of frequency filtering, while incorporating several real world system complexities into the general analytical solution.
Several recent advances in optical pattern recognition are described as they apply to terminal missile guidance. Practical pattern recognition aspects are emphasized, specifically maintaining correlation in the presence of expected differences between the input and reference imagery.
Analysis techniques and trade-offs leading to the design of an LWIR exoatmospheric optical system are outlined. The use of the ACCOS V and Polypagos Optical & Analysis programs and the APART Baffle Design program are discussed. Studies are outlined which include lens design, material reflectivity, baffle scattering, baffle diffraction, thermal warm up and low temperature distortion.
An automated system for scanning missile domes under computer control at an arbitrary number of points and determining both forward scattering and transmittance from 0° to over 60° from the dome axis is now in operation. Measurements at 3.39 pm have been made on both unused and used domes, artificially eroded domes, and also on pieces of spinel, which is a possible replacement for the magnesium fluoride now used as an infrared dome material. A total of 18 new, 1 used, and 2 artificially eroded domes have been measured. Data indicate that (1) the scattering and transmission is nearly uniform as a function of angle away from the dome axis for the used dome as well as for new domes, (2) the scatter from the used dome was higher than that from 15 of the 18 new domes, but less than that for 3 of the new domes (26% more scatter than the average of all the new domes), and (3) the sample of press-forged, single-crystal spinel scattered 5 times less than the average of the new domes, while the fusion-cast polycrystalline spinel sample scattered 2.5 times more than the average.
The Infrared Simulation System (IRSS) at the Army's Redstone Arsenal is used to test small air-to-air IR guided missile seekers. The IRSS optics provide a dynamic field of view containing dynamic targets and backgrounds and are designed to operate over the wave-length range from near UV to 5 µm. We have studied ways in which this system could be modified so that it can also be used for testing small air-to-ground missile seekers operating passively in the 8 to 14 µm window., The existing optical system is an Offner Concentric Mirror Annular Field Projector (l) in which the secondary mirror has been dimpled to expand the input beams and allow superposition of the fields of several relatively narrow input beams. In the thermal IR this dimpled mirror inserts copious ambient radiation into the system which must be allowed for. Further in the air-to-ground case the background closes with the target whereas in the existing simulator the background is assumed to remain distant. The limitations imposed by these factors will be discussed as will the practicability of less and more sophisticated methods of circumventing these limitations.
Hughes has developed many target simulators and special test instrumentation devices. These range from very complex total missile flight simulators to very simple point source or bar-target collimators. This paper will discuss Hughes' simulation approach which involves a compromise between model accuracy and fidelity, simultaneous control of many properties, and cost, both non-recurring and recurring. Simulators will be described that define our concept, which is based on dividing the functions of target simulation complexity into user oriented test and the electromagnetic band into the spectral content of targets. The test complexity levels were divided into three user activity functional needs: a) conceptual development using analog simulation: b) tracker development using real spectrally simulated targets for testing subassemblies, seeker general performance, and seeker terminal guidance; and c) semi-physical simulation utilizing the missile system's flight dynamics, from launch to impact. Each of these three user oriented, functional test levels was again divided into four spectral bands of target simulation: a) visible, b) laser designator, c) 3 to 5 micron, and d) 8 to 13 micron. Pictures and performance data of each of the above target simulation devices will be presented.
One of the basic concerns of Exoatmospneric R.diometry is the spatial rejection of naturally present background radiation while viewing a low intensity source. This paper presents the technique for assessing this sensor quality as well as the associated problems. The basic measurement technique utilizes a CO2 laser operating at 10.6 micro-meters. The beam is expanded and recollimated to a 13 inch diameter. The focal plane sampling system utilizes a mercury cadmium telluride detector cooled to 77 degrees kelvin. Detection data is sam led with a lock-in voltmeter synchronized to the chopped laser beam. Results from two sensors are presented and demonstrate a m easurement capability of 12 orders of magnitude dynamic range.
This paper reviews briefly the key elements required for closed-loop simulations used to evaluate infrared guided missiles in an infrared countermeasures (IRCM) environment. The general requirements for semiphysical simulation are reviewed, including special requirements which arise due to IRCM considerations. The US Army's Dynamic IRCM Simulator is used as an example. The paper describes infrared sources, reflective and refractive optics, associated servomechanisms, calibration instrumentation, and computation equipment. Note is made of the requirement for multispectral band, future generation semiphysical simulation.
ON-AXIS precise pointing and tracking systems were developed to provide high resolution optical imagery of missile and satellite targets. They consist of specially designed mounts for radar or laser active sensors with boresight optics to calibrate the mount to the celestial sphere at multiple points. With sources of error constrained to predetermined limits or modeled, the computerized system accepts observational data to generate highly accurate real time state vectors in digital adaptive control loops con-verging to the actual sta a of the vehicle in geocentric space. Large (48 inch aperture) remote electro-optical systems are driven by the state vector providing smooth tracking and high resolution (to a few feet) images of ballistic missiles and near earth satellites. Synchronous and other deep space objects are detected as point sources however major events such as thrusting are monitored by observing large scale phenomena associated with the rocket motor plume. Results of data obtained from tests will be presented.
A comprehensive hardware-in-the-loop simulation has been developed, operational in real-time, to perform guidance and control system design verification and autopilot and detector optimization for a laser semiactive terminal homing weapon system. Emphasis was placed on the development of time-critical aspects of the simulation including analog-digital computer partitioning, aerodynamic moment updating, and target-vehicle geometry modeling. Validity of the simulation was demonstrated by comparing results obtained from the all digital 6-DOF and hybrid analog-digital simulations. The simulation was proven an invaluable evaluation and optimization tool in efforts to enhance weapon system performance.