This paper discusses the major design tools utilized at the Night Vision and Electro-Optics Laboratory (NVEOL) for analyzing electro-optical sensor systems. The Thermal Static Performance Model is described as an example of the methods used. The other systems models are based on the same concepts both in analysis and computer programming. The basic approach for all the laboratory and field models is tied to measurement techniques. The models provide a set of tools to write specifications, design systems and analyze requirements. The basic thermal model code, its use, and limitations will be explained. The current version utilized at NVEOL makes use of an interactive input data structure, and includes a graphics package for field performance. Similiar models exist for image intensifiers (II), television (TV), and aided/unaided eye. These models however are not as widely used and therefore have not received the same level of resources as the thermal models. All of these models enable one to predict performance against a variety of target configurations and atmospheric conditions including smoke. The use of the computer programs is illustra-ted.

SPIRE (Simulation of Passive Infrared Equipment) is a set of computer programs and subprograms for simulating infrared systems which consist of optics, detectors, and signal processing electronics. SPIRE represents in detail the image plane irradiance distribution, integration by the detector array, and subsequent sianal processing of the detector outputs. The simulation of a missile-borne infrared tracker will be described and some conclusions concerning the tracker design and performance will be presented.

This paper discusses a simulation tool and its application to the definition and development of several critical signal processing algorithms. These algorithms are used in conjunction with a sensor to provide for the detection and resolution of a target complex consisting of several thousand objects. This detection and resolution problem is complicated by the fact that many of these objects are contained in high density clusters that occupy less than a single square degree of the sensor's field of view. It was found that the detailed development of these signal processing algorithms, as well as downstream data processing algorithms, depended heavily upon the implementation and use of high-fidelity sensor and threat scenario models. These models provide the capability of generating accurate detector voltage trains representative of both simple and complex scenarios in support of algorithm concept evaluations. Significant sensor characteristics that are modeled include: (1) the focal plane geometry, (2) detector waveshape (responsivity effects), (3) signal conditioning electronics effects, and (4) sensor-associated anomalies. The threat model includes the significant metric and radiometric characteristics of the objects complex as viewed by the sensor. The partial evolution of one key signal processing algorithm--closely spaced object resolution--is traced as a means of illustrating the utility of the simulation as an algorithm development testbed.

Infrared electro-optic sensors for target detection, tracking, and imaging applications continue to play vital roles in many military and scientific programs. The sensor and its components must be optimized for each application. A critical part of the optimization is the end-to-end modeling and experimental evaluation of the integrated sensor functions. In nearly all cases, only computer simulations are performed using actual or assumed component data with no experimental verification of end-to-end sensor performance due, pri-marily, to a lack of facilities. In this paper we describe a brassboard test facility specifically designed to experimentally evaluate the end-to-end performance of both scanning and staring IR sensors. The facility has the capability of providing a wide variety of target and background signals and image scenes in several spectral regions to IR focal planes interfaced to a fully dedicated on-line minicomputer facility. The minicomputer provides the required data collection and signal processing capability to evaluate various sensor component and end-to-end sensor functions in real or near-real time. As an example, some test results for a brassboard IR passive tracker are shown.

This paper describes an image sensor performance model which can accommodate aperiodic and periodic image patterns of arbitrary size and shape and which is applicable to a variety of electro-optical sensor systems in any spectral region. Performance predictions have been validated experimentally. It is especially effective for IR FPA systems used to acquire low contrast thermal imagery because of the accuracy of describing the multiplicity of noise components produced by the arrays. Use of this model is illustrated for typical ground and airborne applications.

The methodology for calculating aircraft infrared radiation is developed by expressing the signature in its component parts and then modeling each in terms of a few parameters. The basic signature components are: exhaust plume molecular emissions, airframe thermal emissions, various exposed engine hot parts, and scattered ambient radiation (e.g., earth-shine, sunshine and skyshine). When calculating sensor irradiances for systems studies, the close relationship between the aircraft signature and environmental conditions must be considered. This is illustrated with scene contrast signature calculations for several different observer viewing angles and background types.

Using an updated modification of the computer program CORPS (Comprehensive Radiance Profile Synthesizer), horizon Profiles can be computed for the specific spectral response of a typical Horizon Sensor System (HSS) for a range of latitudes for every month of the year. These Profiles can be used to model the earth's atmosphere, primarily at the horizon. Using the earth model developed in this way, the operation of a particular HSS can be simulated and error due to radiance variation computed. Block diagrams of the computer programs are discussed and performances of two different HSS instruments are evaluated to demonstrate the flexibility and general usefulness of this approach.

Using a computer program to model the earth's horizon and to duplicate the signal processing procedure employed by the ESA (Earth Sensor Assembly), errors due to radiance variation have been computed for a particular time of the year. Errors actually occurring in flight at the same time of year are inferred from integrated rate gyro data for a satellite of the TIROS series of NASA weather satellites (NOAA-7). The k)recLicted performance is compared with actual flight history.

The concept of optical image quality is extended to include the total electro-optical system performance. A complex software package called the End-to-End simulation has been developed with the total system performance as its merit function. The example discussed has as its merit function time delay errors. Subsystems modeled include the object, the "real" optical system, the detector and its associated circuitry, and the electronics used in signal processing. Validation of the modules comprising the total package is discussed.

It is often advantageous, when faced with the necessity of characterizing or recognizing a distant source, to measure the spectral distribution. This is normally done with a scanning Michelson interferometer fed by a large collecting telescope. The effect of errors in the Michelson interferometer has been analyzed by several sources,1,2 but little work appears to have been done on the effect of aberrations introduced by the collecting telescope.

The thermal design requirements of infrared sensors are discussed as they relate to nodal network modeling for thermal performance predictions. The use of the CINDA thermal analyzer program for the solution of the network problems is described, thereby demonstrating the program features which need to be invoked to handle the varying thermophysical properties associated with cryogenic temperatures. An example of steady-state and transient analysis utilizing CINDA is given.

Various optical design techniques and examples are Presented for users of programmable pocket calculators. Third-order analysis and real ray tracing of up to tenth-order aspheric surfaces is performed with available calculator programs. Design examples include the computation of optical path difference (OPD), ray tracing decentered systems, root-mean scuare best focus for spot diagrams, image tilt in an off-axis parabola, a comparison of third-order aberrations relationships, ray tracing with a third-order ray-trace polynomial, third-order spot diagrams, some selected first- and third-order design principles, a comparison of surface profile equations and how to convert between them, and a holographic optical element design example. In addition, the computation of the diffraction point spread function for annular aperture and rectangular aperture systems is described.

A macro that facilitates analysis of thermal effects on optical systems has been written for the ACCOS V optical design program. Details of the macro operation are described and specific examples<are provided. A computer listing of the macro is also included.

Hybrid focal plane devices with photovoltaic detectors mated to charge-coupled device (CCD) multiplexers are finding applications in an increasing variety of staring and scanning sensor systems. This paper presents analytical models for the modulation transfer runction (MTF) and the noise in a sensor system which uses hybrid focal plane devices. The MTF model treats principal sources of MTF degradation within the detector chip, the CCD, and signal processing. The noise model treats fifteen noise sources within the detector and CCD, and also accounts for noise generated in the signal processing chain. Both models are applicable for either staring or scanning sensor systems. Limitations of the models are discussed.

A methodology is examined to develop a computer-based life cycle cost model for optical systems. This methodology consists of six major steps or tasks for the investigator. These tasks involve the identification of the major program and cost elements, the structure and programming of the model, the acquisition of data, and initial cost sensitivity analyses using the computerized model. Lessons learned from past computer life cycle cost modeling efforts demonstrate the many difficulties in obtaining accurate, absolute cost estimates. The most effective models are those which accomodate the quality and quantity of the data base and are structured for cost sensitivity and cost comparison analyses.

Unit production cost and life cycle cost tradestudy considerations are basic to the affordability of a new product. A major portion of the life cycle cost of a product, including production cost, are found to result from decisions made early in the planning phases of a program. Computerized parametric cost modeling generates cost estimates using the information that is available before the developing of engineering detail. The RCA PRICE program, available to all potential users, is used to illustrate the input requirements and steps necessary for parametric estimating of costs for development, production and support in the life cycle of a product. A laser rangefinder equipment is used as a product example to show the utility of this analysis.

The successful development of various electro-optical systems is highly dependent on precise electronic circuit design which must account for possible parameter drift in the various piece-parts. The utilization of a comprehensive computer analysis program (SYSCAP II) provides the electro-optical system designer and electro-optical management with a well-structured tool for a comprehensive circuit analysis. An overview of the SYSCAP II program is being presented with examples applicable to electro-optical design problems. In particular, the program has been used for extensive radiation effects predictions of semi-conductor response to various transient and permanent radiation effects. Worst-case, Monte Carlo, and component failure simulation (CFS) are discussed with respect to the electro-optical design challenges for the 1980s, including "design for producibility". The SYSCAP II program is provided through Control Data Corporation (CDC) with Rockwell International providing the technology under a licensing arrangement with Control Data Corporation. As a result, the techniques described in this paper can be readily used by the electro-optical design community.

Optical sensors have received wide acceptance to military and space applications. Their survivability in the natural space environment, nuclear weapon environment, and weapon enhanced space radiation has become a major concern. Nuclear radiation has two basic effects which interact to compound the degradation in detection systems. First, the nuclear radiation degrades the performance of the sensors by reducing minority carrier lifetime and increasing leakage currents. Second, the nuclear radiation acts as a noise source per se, thus decreasing the signal-to-noise ratio of the detector system. Still another complicating factor adds to the system problem. The output signal from the sensor is very low level and must be amplified by semiconductor electronics. The semiconductor electronics are also significantly degraded by the nuclear environment. This paper will attempt to summarize the problems and describe the radiation hardening techniques which are used to improve the operation of sensor systems in the nuclear and space environments.

Experience gained in computer-aided design of an arsenic doped silicon detector-JFET preamplifier having switched feedback resistors operated at 12°K is reported. In order to reduce the time involved in the designer-computer iterative loop it was found advantageous to utilize more than one computer-aided approach. Both a large general-purpose simulator (SPICE) for assessing the effects of adding parasitic elements and smaller dedicated computers with software restricted to special cases were found to be useful.

The types of computer software required to support computer aided design (CAD), end-to-end computer aided analysis, computer aided manufacture (CAM), and computer aided test (CAT) of electro-optical sensor systems are described. This discussion includes the role each software area plays in the total systems package, and how they interrelate with each other. The problems involved in implementing this software in computer hardware and software are also discussed.

The panel discussion was designed to cover the following topics: issues in selection of hardware, size and concentration of computer power, scheduling and access; the interface between the engineers who use an engineering facility and its operating procedures, type of software, and methods of user training; what can be expected of the engineers and what should be done for them by the installers and operators of the facility; portability of software; considerations in use of standard vs. installation-special software; time and cost required to set up facilities of various capabilities; characteristics of future facilities.