Optical systems engineering is just beginning to come of age. The combination of new metrology, new manufacturing techniques, computer based analytical tools, and the stimulus of several premier optical programs are leading toward a fuller and more complete exploitation of the systems engineering approach to the design, development, fabrication, and operation of high performance optical systems. Systems engineering which involves an integrated interdisciplinary approach to the development of systems is most appropriate for optics. The very high precision character of optics leads to very complex and subtle effects on optical system performance, resulting from structural, thermal dynamical, control system, and even manufacturing and assembly considerations. The systems engineering approach is thus more important to optical system development than most other types of systems. Optical systems are sufficiently unique that communication problems often occur among users, optical engineers, and the rest of the systems team. It is essential that the optics community provide leadership to resolve communication problems and fully formalize the field of optical systems engineering.
The US Army Laser Measurement Assurance Program (ALMAP) involves the on-site experimental evaluation and assessment of selected US Army, DOD, and Contractor laser measurement capabilities so that close measurement agreement can be achieved. In this paper we describe what a Measurement Assurance Program (MAP) involves, the specific goals of ALMAP, and our present status in achieving these goals. Finally, we analyze some ALMAP results which demonstrate the benefits of MAP's in general and ALMAP in particular.
The evaluation of the interactive nonlinear performance of an electro-optical system is often best achieved by exercising the system in the context of a simulated environment which provides more complex and realistic stimuli than bench tests at less cost than field testing. The systemic behavior of an electro-optical device, test goals, and simulator resources jointly constrain an appropriate simulation environment. It is the responsibility of the simulation specialist to recognize the peculiar qualities of the object system and to provide for it an environment which, in its relevant characteristics, is practically indistinguishable from the real world,and which is sufficient to exercise the system over its entire stimulus domain. To illustrate this thesis, the location of a hypothetical missile seeker/tracker in the context of a hardware-in-the-loop (HWIL) simulation will be established and the manipulable features of its environment illustrated. Some aspects of such a device's response to its environment which have required special attention will be discussed.
Special systems problems encountered in the development of hardware/man-in-the-loop simulations of missile systems are discussed. The contents of the paper are based on a US Army Missile Research and Development Command (MIRADCOM) simulation development program that resulted in a new end game simulation capability for systems employing imaging sensors and a variety of optical trackers. Emphasis is placed on the integration of optical systems which are designed to operate in the real world into a laboratory environment. The requirement to simulate the entire missile flight profile from launch to intercept posed unique problems to the optical system, especially in the end game where depth-of-field becomes critical with the small closure distances necessary to represent reasonably small missile/target separations. The solution to this problem involved the development of special optical and mechanical equipment that was integrated with the sensor and tracker elements.
To evaluate an optical sensor's performance capabilities for specific system applications, it is often cost-effective to simulate the optical component's response to the intended environment and the subsequent effect on the system's performance. High-fidelity computer simulations have been developed which provide valuable assistance to hardware development programs. The elements and techniques of optical system simulations are described, accompanied by samples of results. Existing high-fidelity simulations are described and computational resources discussed.
During the last few years manufacturing test engineers have been exposed to a new set of terminologies that include lasers, laser safety, isolated test areas, clean rooms, precision fixtures, assembly procedures, and alignment procedures. In addition to the changes in terminologies, both research and development engineers and manufacturing test engineers have found themselves responsible for test procedures and assembly procedures due to the requirement of alignment and alignment checks during and after assembly of electro-optical systems and subsystems. Due to the changes in engineering responsibility, management has made several small but general changes to ensure an earlier interface during the research and development phase between the manufacturing and research and development organizations. Because this early interface has been missing with some of the earlier electro-optical systems, the process control efforts in manufacturing have not kept pace with the research and development areas. Examples of areas in process control in which there are great and immediate needs for advancement include bonding of optical components, optical coatings, and mechanical mounts. It is the intent of the author to present both problems and solutions encountered during past projects and to point out anticipated problems on future systems and how this new knowledge is being used to head off future problems.
This is the topic of our presentation today and I would like to share with you the system through which MCI has been able to develop efficient and economical optic systems. We have been able to establish this type of program through our experience of working with our customer and his needs.
Missile test sets require a standard against which they can be calibrated and compared. A transfer radiometer has been developed for this purpose. This radiometer is calibrated against a primary standard and becomes a secondary calibration standard which is used by replacing the missile in the test stand. The transfer radiometer is fully compatible with the test set from the aspects of mechanical, radiometric, optical, electronic and total system adaptation and can be considered as a black box which engineering and technician specialists can use with ease without comprehending its internal operation. The paper describes the concepts and operation of the transfer radiometer and its method of use.
The practice of cooling an IR detector by mounting it on the cold finger of a small mechanical cryogenic cooler can cause some degradation of system MTF and other problems due to vibrations produced by the cooler. A balancing method has been devised, involving simple internal design changes and no external configuration changes, which reduces these vibrations by more than an order of magnitude. The principal vibrations are caused by the reciprocating masses of the piston and regenerator and by the unbalanced rotating masses on the eccentric shaft. The vector sum of vibratory forces caused by two equal reciprocating masses in the same plane, driven in simple harmonic motion with 90° phase difference by the same eccentric shaft, is equivalent to the force produced by a single mass equal to one of them mounted on the eccentric shaft. To balance the cooler, the regenerator assembly is modified to make its mass equal to the piston assembly mass and balance weights are added to the eccentric shaft at 180° from the eccentric center to balance both the rotating and reciprocating masses. Coolers have been built incorporating these changes.
Although the performance of self scanned arrays would be increased if they were cooled, there are applications where this increased performance may not be required. However, there are applications where self scanned arrays must be cooled to provide the required performance. Typical applications that require low temperature cooling are low light level, long time stare applications; and cameras where dark spots must be held to a minimum. Low temperatures in the range of -40°C to -50°C are ideal for thermoelectrically cooled self scanned arrays. A thermoelectric heat pump is a small, solid state, efficient method of cooling self scanned arrays. A typical system consisting of an enclosure and thermo-electric heat pump is described.
The design of airborne electro-optical systems requires the knowledge of angular vibration as well as the conventional linear vibration of aircraft structures. Rather than predicting the angular vibration subject to aerodynamic and acoustic excitations, an attempt is made here to relate the angular vibration directly to the linear vibration response. With the Bernoulli-Euler beam used as a theoretical model, a relationship has been derived between the linear and angular vibration power spectral density functions. From this relationship together with the angular vibration energy already predicted by Lee and Whaley (AFFDL-TR-76-55, Wright-Patterson AFB, Ohio, 1976), we can now predict the angular power spectral density at an arbitrary aircraft location. Tested on the typical flight test data of RF-4C and F-15 fighters, CH-3E helicopter, and B-52 bomber, the predicted angular power spectral density lies within ±10 db of the measurement over the whole frequency range. Though crude, such a prediction is useful in the preliminary design stage, whereby one can quickly and simply obtain a first-order estimate of angular vibration from the prescribed linear vibration environment.
The SUPER RADOT videometric tracking system is currently being installed at the U. S. Army Kwajalein Missile Range (KMR) in the Kwajalein atoll of the Marshall Islands. A companion piece of equipment, the Video-metric Analysis and Reduction System (VMARS) has been installed at the KMR Honolulu Data Reduction Facility, Honolulu, Hawaii. Sufficient metric data have been obtained and processed through this new equipment to describe the field operations and data processing experience which have been gained, discuss changes in original concepts which have been required, document results obtained and to discuss planned systems improvement.
Presently Army systems are under development to perform long-range engagement of tank type targets with Antitank Guided Missiles (ATGM) from heliborne platforms. This gives rise to the requirement for systems to perform long-range target acquisition. In order to recognize a tank target from low altitudes (nap-of-the-earth), at long standoff ranges, and under realistic battlefield conditions, a number of complex system design problems must be solved. High acuity electro-optical sensors which are needed to achieve recognition criteria require precision inertial stabilization of the line-of-sight (LOS). This problem is particularly difficult when the mission is performed under the dynamic environment of an attack helicopter. Various LOS stabilization concepts have been investigated to determine their relative merits with respect to meeting the precision stabilization performance requirement.
The Tracking Instrument Mount (TIM), originally developed for NASA by the Naval Ordnance Test Station, China Lake, California, and consisting of a 36 inch Cassegrain telescope and hydraulic driven, cable wrap mount, has been adapted to meet SAMTEC requirements and installed at the Anderson Peak Site in Big Sur, California. The location provides excellent coverage for westerly missile launches from Vandenberg Air Force Base, California. System design considerations during performance of this task include: site selection and prepartation, mount drive system refurbishment and modifications; telescope optical component replacement and modifications; and sensor interface development. The foundation is the result of a soil study and is designed to provide vibration isolation and stability. The Ritchey-Chretien Cassegrain configuration was selected for minimum field of view errors to optimize data from low light level television for detection and measurement of reentry vehicle deployment. Other features include a remote controlled 288 through 1440 inch reimaging system, primary mirror pneumatic-mercury belt support system, remote controlled neutral density filter turret, and piggyback telescopes. Predicted optical performance values are presented.
The Rotating Spin Mount/Data Acquisition System provides visible and IR imaging coverage of wide area terrain as seen from a helicopter or high tower. Data from both sensors is TV compatible and can be stored on video tape together with position and timing information. The visible and IR cameras are mounted on a rotating mount which spins at precisely controllable rates up to 15 r.p.s. The look angle is adjustable from straight down to horizontal. A single vertical array of detectors is used in each camera, with horizontal scanning provided for by the spin mount motion. The visible camera uses a 256 element CCD array while the IR camera, operating in the 3 - 5 micron region, makes use of a 64 element T.E. cooled Lead Selenide detector array. One application of the system is a test bed for the evaluation of various air to ground armament sensors. The cameras are used as confirming sensors for both daytime and night-time tests. The target detect signal from the sensor under evaluation is recorded on the imaging data as a cross hair. Design techniques and criteria are presented for both cameras and the spin mount along with a discussion of the particular problems and special requirements encountered for this application. Auxiliary equipment which will greatly extend the usefulness of the device is also presented along with future uses which include wide area target and background data collection, surveillance and target search and location.
Previous design approaches for precision tracking systems concentrated on the sensor and the signal processor as independent subsystems at the expense of the overall system design. This previous approach resulted in excellent sensors and processors, but quite often the combination was not optimum. Under Air Force contract, the Aeronutronics Division of Ford Aerospace and Communications Corperation developed a precision tracking system consisting of a high resolution FLIR and a computer based signal processor. While each component was an advance in itself, the biggest advance resulted from the successful integrated design of the system. For example, the tracking algorithm compensates in real-time for scanning inaccuracies in the sensor. This algorithm overcame previous tracking accuracy limitations and also relaxed tolerances on the scanner. This paper discusses the design of the tracking system and presents test results demonstrating the improved performance. It also describes a procedure by which the sensor of a tracking system can be optimized for a given processing algorithm. This procedure allows system designers to specify performance of components based on an analysis of the total system's desired performance.
A large variety and number of electro-optic (EO) systems have been developed for radar, communications, platform guidance, sensor functions, etc. In considering these applications many technical questions regarding undesirable electromagnetic (EM) effects which may degrade the operation of an EO system are apparent. Information and data related to these effects is presented. These effects include atmospheric scattering, dust and chemical films on apertures, and edge scattering effects which are expected to modify the theoretical diffraction pattern. Emission spectrum characteristics in terms of sideband, spurious, and harmonic energy as well as RF emissions are discussed. Out-of-band response of EO detectors and filters, spurious responses due to non-linearities, detector desensitization, and RF frequency degradation effects on EO receivers are considered. The analogy of EO systems to RF system problems is stressed to illustrate the potential loss in performance due to these undesirable effects.
A new and optically very simple Michelson Fourier Transform Spectrometer has been developed. The development includes full consideration of the data processing problems and their solutions. The raw data are recorded on analog tape at the telescope, but digitization and all succeeding reductions are performed by digital computers. All the necessary data reduction software is complete, and we demonstrate that they produce spectra whose resolution compares favorably to the 5- and 16-A/mm Coude spectra in the Hiltner and Williams Stellar Spectral Atlas. The first results from this spectrometer have been published as "An Atlas of Stellar Spectra," Volumes I and II, whose wavelength coverage is between 0.4 and 1.0 pm. The atlas is available in digital tape format from the National Space Science Data Center, NASA-Goddard Space Flight Center, Greenbelt, Maryland 20771.
An optical path error suppression system was developed for a helicopter-mounted pointing and tracking system. Tests show the system can measure both static (thermal) and dynamic (vibration) angular changes of less than 5 microradians (1 arc second) between the folding mirror surfaces in the optical path line of sight. Collimated rays from a pulsed laser diode are projected along the optical path. A dichroic mirror returns the diode wavelength to a detector. The detector signals are processed into elevation and azimuth angular error components. A feedback controller converts the error signals into corrective commands to the servo-driven stabilized mirror. Tests of the system which simulated the helicopter vibration environment showed RMS line-of-sight errors were reduced from 56 µR to 7 µR, an improvement of 800%.
This paper describes how system acceptance testing can be performed utilizing an inter-ferometer both for subsystem and final system performance requirements. The performance of optical systems can usually be translated into wavefront specifications. Specific instrumentation described using these types of tests include scanning mirror assemblies, zoom lenses, alignment telescopes, spotting scopes, and various types of other image forming instruments.
Heretofore, there are many literature concerning the measurements of transfer function for a control system, (1) (2) but very few on the topics for an E-0 system especially for the part containing both the sensor and its signal processing. The purpose of this paper is to give a simple new approach to characterize the E-0 transfer function in frequency domain. The main contributions of this approach are namely: (1) A moving target generation, which is made by the light source array is designed to simulate a moving target. The advantages of this set up will give simplicity and high frequency capability. (2) A programmed numerical optimization process, which makes use of the least-squared-error method is established to locate the pole-zero configuration of over all system. (3) An experiment for the TV tracking-centroid system is developed to illustrate the details of this approach. The results reveal the 15 db band width of which at 0.639/um wavelength in low light level condition is 8 Hz. It is suggested that this technique can also be applied for many other E-0 systems such ass infrared, laser and so on extensively.
Contemporary long wavelength infrared (LWIR) technology offers potential improvements in Ballistic Missile Defense (BMD) systems. The Designating Optical Tracker (DOT) program being developed for the BMD Advanced Technology Center (BMDATC) is the latest sensor in a series of development and flight test programs. A DOT flight consists of an exoatmospheric probe launched from Kwajalein Missile Range (KMR) engaging a reentry vehicle train in the downrange portion of its flight from the Western Test Range (WTR). An essential step in preparing for each flight is calibration of the LWIR sensor sub-system. Basic performance and functional tests are performed by the supplier, Hughes Air-craft Company, and by Boeing during integration and vehicle-level tests. Detailed radio-metric calibration was performed at the McDonnell Douglas Advanced Sensor Evaluation and Test (ASET) facility. Tests were performed to determine the DOT sensor subsystem performance parameters, typical of those required by other LWIR sensors, to investigate sensor/ detector phenomenology, and to evaluate the proposed sensor timeline to be used during the mission. This paper describes the specific sensor parameter under investigation/calibration during each ASET test, the type of data collected, and the results of the data analysis.
Equations are derived for the design of BLIP infrared sensors starting from system functional performance requirements, including source intensity and range, field of view, frame time, closely spaced objects that are to be resolved, background radiance, and minimum signal-to-noise ratio. The sensor design parameters that are of primary importance because of weight, volume, and cost considerations are the sensor aperture diameter and the total number of detectors. The design equations are written in terms of these parameters, and a graphical technique is presented that defines the limitations on tradeoffs between them. The performance capabilities of scanning and staring sensors are compared. It is shown that the sensitivity of a scanning infrared sensor, whose performance is background-limited and whose scanned field of view and frame time are fixed by system requirements, is independent of detector size and inversely proportional to the square root of the number of detectors.
Possible optical processing techniques which could be applied to infrared (IR) guidance systems are discussed and a program plan for developing the necessary hardware is proposed. During this program, optical techniques which can be used to manipulate or analyze the incoming IR energy prior to detection by a focal plane array will be investigated. Present IR seeker systems use little of the available information contained in the target radiation due to limitations in electronic detection techniques and processing capability. The next logical step beyond focal plane arrays is to develop systems which use spectrum analyzers, tapered fiber bundles, Fourier transforms, and optical switches to increase target detection range and reduce electronic complexities.
A few mosaic focal plane sensors (to permit high data throughput) appear to be cost effective for space surveillance relative to larger numbers of low throughput sensors. Energetic space radiations generate noise which can be reduced by data processing. Throughput requirements dictate digital processes, which creates interest in digital noise reduction algorithms. Algorithms that reduce the noise due to Poisson distributed bursts of conduction (such as those which result from ionizing radiation and "spiking") in LWIR detectors were synthesized and evaluated using Monte Carlo techniques. These algorithms were chosen to provide improved performance at high event rates and for compatability with low background LWIR sensor systems using large numbers of detectors. The results show that quite useful sensor perfoTance 4s attainable for credible ranges of sensor parameters and for event rates in the range of 10 to 10 per second per detector. Also, signal amplitude and tracking accuracies are preserved at the expense of data throughput, whereas most current algorithms have exhibited large degradations in amplitude and track accuracy. While the data processing burden has not been assessed in detail, it is believed to be similar in magnitude to that for other algorithms which are being considered.