The recently developed, simple and highly accurate technique for self-calibration of the absolute response of a silicon photodiode is described. The silicon photodiode self-calibration (SPSC) technique is independent of both electrical substitition radiometers (ESR's) and blackbodies - the traditional standards of absolute radiometry. Using the SPSC technique one can obtain high accuracy over a limited wavelength range with a very small investment of time and money. This means that the SPSC technique can be conveniently used to calibrate an ESR, thus avoiding the long and tedious characterization measurements required to evaluate the radiant to electrical power calibration factor of an ESR. The wavelength dependence of the ESR calibration factor arises from variations in the reflectance of the coating used as a radiation absorber. By measuring the spectral variations of reflectance one can use the SPSC calibrated ESR to measure the absolute response of other detectors over a broad spectral range.

The Aerospace Guidance and Metrology Center at Newark Air Force Station has the highest echelon of traceable calibration standards for the U S Air Force, including the laser and infrared measurement areas. The number of sophisticated electro-optical systems in the Air Force is growing rapidly, requiring a standards lab with both traceable standards and versatile measurement apparatus. The laboratory calibration facilities and typical measurements are described, with emphasis on the infrared. Of special interest are unique constraints imposed by the system under calibration.

Over the past several years, the U.S. Navy has generated a requirement for the calibration of Forward Looking Infrared Systems (FLIR). This paper describes the calibration of a radiometer used to transfer the change in radiance per degree Celsius of a National Bureau of Standards (NBS) calibrated blackbody to a blackbody located in an infrared test bench. The test bench is then used to calibrate FLIR systems.

In the past, blackbody simulator cavity shapes have been chosen by intuition and experience, combined with selective comparisons among candidate cavity shapes using one or more blackbody simulator cavity theories. Popular candidates have included cones, cylinders, spheres, reentrant cones, and lidded cones and cylinders; the usual choices have been cones. This paper describes a new family of blackbody simulator cavity shapes with improved uniformity of cavity emissivity and a tendency toward uniform cavity temperature.

The new broadband spectral radiance standard consists of a specially modified tungsten ribbon-filament lamp with an optical grade, sapphire window. The lamp is calibrated for spectral radiance over the 0.25 to 6.0 μm wavelength region. The standard serves as an accurate, convenient alternative to the much more costly high-temperature blackbody standard currently available.

Radiometric testing of low background, long wavelength, infrared (LWIR) sensors using laser sources is a viable alternative to testing in cryogenically cooled space simulation chambers. However, in testing with lasers, care must be taken to prevent errors introduced by coherence effects.

A review is presented of some of the more common pitfalls encountered in measuring and using thin-film interference filters. Measurement difficulties, including angle-of-incidence effects and the influence of instrument polarization and cone-angle, are described as well as problems such as the "Stierwalt Effect" which create difficulties in usage. The presence of imaginary "leaks" which appear in measurements and true "leaks" which do not show up in spectrophotometer scans (but do appear in your application) is discussed. The authors suggest measurement procedures and application techniques intended to circumvent these problems where possible.

It is desirable to use thermal detectors in spaceborne electro-optical (EO) systems where the required system performance allows their use. Thermal detectors require no cooling, are stable and rugged, have good uniformity, can be made with large active areas and are broad band, spectrally. The Earth Radiation Budget Experiment (ERBE) is a system in which the properties of thermal detectors, in this case thermistor bolometers, are not only acceptable but are also desirable. The application demands sensing of wide band IR radiation and since the measurements are radiometric ones in which small changes in a large background are to be measured, extremely stable, well characterized detectors are required. This Paper discusses the criteria which characterize good detectors and also describes some of the in-process and final tests that were performed to ensure the delivery of detectors meeting system level requirements.

A new airborne multispectral scanner system was assembled and installed in a De Havilland DHC4A (Caribou) aircraft. This system was used to collect two sets of imagery; one set for strategic target areas near Sunnyvale, California, and another set for target areas near Rome, New York, during the time period July-November 1978. The imagery was processed and distributed to various researchers for use in studies of advanced scene-matching techniques as part of a program to provide precise autonomous guidance for strategic delivery vehicles. The sensor system produces seven data channels, all in spatial registration-visible, near infrared, thermal infrared, 1.06 μm laser reflectance, 10.6 μm laser reflectance, 95 GHZ radar reflectance and 1.06 μm laser range. All optical channels had a 1.25 mrad field of view and the radar has a 7 mrad two-way antenna beamwidth. The data were digitized and re-corded on a high-density digital magnetic tape recorder along with aircraft altitude from a radar altimeter and aircraft attitude and acceleration data derived from an inertial navigation sensor. A nine-inch format metric camera was boresighted with the sensors and provides additional information on aircraft position through use of inscene surveyed benchmarks. A key feature of the system was the dual-frequency modulated 1.06 μm laser ranging unit that provides absolute range from the aircraft to each pixel in the scene. The range data, the camera photos, and the inertial navigation data all provide inputs for geometrical reformatting of the imagery to remove distortions caused by aircraft motion and reconstruction of imagery either in the original line scan format or a single point-of-view format. The topic of the paper is the calibration aspects of this data base with the major emphasis being placed upon the geometrical reconstruction of the data.*

Optical stimulus applied to radiation receiver Units Under Test (UUTs) and transduced measurements of emitted radiation from electro-optical UUTs are just as subject to control and calibration as are their electronic counterparts in the ATE equipment complement. The unique character of the instruments performing these calibrations, alone with some militarized versions of these devices, are presented in this paper. Present and future calibration requirements, with reference to a currently active program, will also be discussed.

Hughes Aircraft Company builds thermal imaging systems which require simulators to verify their performance. The differential temperatures of these simulators need to be calibrated to close limits and to be traceable to the National Bureau of Standards (NBS). In this paper, some of the commonly overlooked calibration problems and solutions are discussed. These include specifications, emissivities, apparent emissivity resulting from ambient irradiance, spectral bandpass of optical devices, and equipment limitations. Also discussed is the calibration philosophy and equipment used by Missile Development Division in Tucson, Arizona.

This paper reviews present calibration techniques for Infrared (IR) Test facilities. The calibration techniques recommended for an automated test facility now being designed and built are also reviewed. The general conclusion is that calibration efforts at different facilities lack common techniques and are not coordinated on a national level. The procedures recommended for the new automated tester would make possible comparisons between test facilities.

The AN/AAM-60 Common FLIR Test Bench includes an infrared target source to provide a test pattern for forward looking infrared (FLIR) systems used on Navy aircraft. To ensure that the Common FLIR Test Bench properly tests the FLIR system, it was necessary to establish radiometric calibration support for the infrared target source. Accordingly, a calibration hierarchy has been established that links the contrast of the infrared target source test patterns to radiometric standards at the National Bureau of Standards. A transportable calibration system has been developed for use by on-site teams in mapping the test pattern with a radiometer. Horizontal lines are scanned by means of a special purpose test fixture utilizing a motor drive on the radiometer mount at selected elevations. The radiometer output is displayed as a function of position on a strip chart recorder corresponding to the scan across the target. The radiometer is calibrated in terms of the temperature of special purpose ambient range blackbody standards at Navy calibration, laboratories. The blackbodies are calibrated by the Navy Primary Standards Department against a master blackbody directly traceable to the National Bureau of Standards.

A method for evaluating out-of-field response of wide-field, earth-viewing satellite radiometers is described. The equipment which simulates the earth and space consists of a central blackbody surrounded by a cooled ring. The radiometric and orbital considerations are discussed. Some test results for prototype ERBE cavity sensors are included. This presentation is restricted to longwave radiative transfer.

This paper describes the equipment used to radiometrically calibrate the Earth Radiation Budget Experiment (ERBE) space-borne instrument complement in a thermal vacuum chamber. The ERBE instruments will monitor on a global, continuous, basis the incoming solar irradiance of the earth albedo, the earth's thermal emission, and the spatial and directional characteristics of the earth's thermal emission and albedo. The calibration equipment described in this paper consists of a master reference black-body source, a short wavelength calibration integrating sphere, an albedo simulator plate, and a space reference source. The design and performance characteristics of each of these sources, as well as the techniques used to provide a radiometric environment for the ERBE instruments equivalent to that of the orbit, are also discussed. Analytical and measured performance parameters of these sources are also described.

The requirements for accurate long-path atmospheric transmission data have increased during recent years. These data are required to further the development of computer models now being widely used for the prediction of visible and infrared electro-optical systems' performance. Some recent examples of long-path transmission data collected with conventional broadband and monochromatic laser transmissometer systems will be presented and compared to current model predictions. The use of large aperture optical systems in long-path laser transmission measurements and the subsequent use of these data for transmission calibration of high-resolution Fourier transform spectra will be examined and examples of recent results will be presented. The advantages and limitations of using laser transmissometer measurements for calibration of both broadband and high resolution transmission measurements will be discussed, making use of these examples.

To develop the full potential of multispectral data acquired from satellites, increased knowledge and understanding of the spectral characteristics of Specific earth features is required. Knowledge of the relationships between the spectral characteristics and important parameters of earth surface features can best be obtained by carefully controlled studies over areas, fields, or plots where complete data describing the condition of targets is attainable and where frequent, timely spectral measurements can be obtained. To meet the need for a standard instrument to acquire these spectral measurements, a multiband radiometer suitable for operation from helicopter, small plane, truck or tripod platforms has been developed. The standard unit is eouinped with the seven Thematic Mapper spectral bands with an added band from 1.15 to 1.30 μm however, up to eight user specified spectral bands from 0.4 to 15 μm may be installed under clean field conditions. The radiometer, with available data acquisition systems, can be utilized by remote sensing field researchers to acquire the large numbers of accurate, calibrated spectral measurements needed. The prototype of this instrument has been tested in the laboratory and field. Results of tests of the spectral responsivity of the detectors, the transmittance of the optical filters as a function of wavelength, the fields of view, and the system linearity, temperature stability, noise performance and dynamic range were evaluated. Minor modifications were made to the instrument and the results of final laboratory testing are reported. All channels were stable in response to input flux changes; linear; adequately stable in response to ambient temperature changes; and all channels met or exceeded signal to noise ratio requirements. The optical coalignment and field of view definition as well as the spectral characteristics of the filters met or exceeded requirements.

Manufacturers of airborne multispectral scanners suggest procedures for calibration and alignment that are usually awkward and even questionable. For example, the procedures may require: separating the scanner from calibration and alignment sources by 100 feet or more, employing folding mirrors, tampering with the detectors after the procedures are finished, etc. Under the best of conditions such procedures require about three hours yielding questionable confidence in the results; under many conditions, however, procedures commonly take six to eight hours, yielding no satisfactory results. EG&G, Inc. has designed and built a calibration and alignment system for airborne scanners which solves those problems, permitting the procedures to be carried out in about two to three hours. This equipment can be quickly disassembled, transported with the scanner in all but the smallest single enaine aircraft, and reassembled in a few hours. The subsystems of this equipment are commonly available from manufacturers of optical and electronic equipment. The other components are easily purchased, or fabricated.