A specially modified Barnes Net Radiometer (Model 12-550) has been used to obtain information concerning the radiative losses from the EPRI/Boeing 1 MWth Bench Model Solar Receiver (BMSR). This solar receiver was tested at the DOE/Sandia Laboratories Central Receiver Test Facility on Kirtland Air Force Base in Albuquerque, New Mexico.
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. The currently available instrumentation systems are either inadequate or too costly to obtain these data. Additionally, there is a critical need for standardized acquisition and calibration procedures to ensure the validity and comparability of data.
A means by which measurements of the optical properties of crops and soils can be knowledgeably compared from site to site and instrument to instrument is presented in detail. The definition of bidirectional reflectance factor is reviewed and discussed. Procedures for field implementation are illustrated and discussed. Spectral and goniometric properties of laboratory and field reference surfaces and typical environmental subjects serve as a basis for analysis of uncertainties introduced by differing illumination conditions. Results of a comparison of the performance of three spectrometer systems are presented and discussed. It is concluded that intelligent use of the bidirectional reflectance factor technique is an accurate and practical means to obtain the spectral, optical properties of crops and soils needed for advancements in agricultural remote sensing.
If a radiometer having a narrow field of view is used to measure the radiance of a source such as a quasi-isotropic atmosphere, a knowledge of the out-of-field responsivity is critical. For example, if a radiometer with a field of view of 5° (full-angle) has a relative responsivity of 10-4 for the out-of-field radiation, the contribution of the out-of-field radiation (assuming an isotropic source subtending 27 steradians) is 102% of the total signal. Either the stray light suppression of the radiometer must be extremely high or methods of determining the out-of-field response must be developed. A description of one method of determining the effect of out-of-field response and its application to a planetary atmospheric radiometer is presented.
Existing commercially available components have been utilized to construct a rapid-scanning spectroradiometer designed primarily for the measurement of underwater spectral irradiance. Irradiance levels are measured at eleven selected wavelengths and the data recorded on a printing electronic calculator. Electronic circuit operation and a method of integrating an inexpensive continuous memory programmable printing calculator as the data acquisition and reduction system will be outlined. The instrument is completely self-contained and may be operated by a diver or triggered by an internal timer. The instrument has been extensively used in marine environments, ranging from a tropical Caribbean coral reef to the Antarctic Ocean, and has proven to be a stable and reliable field instrument. The major advantage of this instrument lies in its small size and rapid easy operation which allow spectral irradiance measurements not feasible before due to the size and complexity of pre-existing spectroradiometers.
Design techniques are discussed for all-reflecting optics from first-order system considerations and applications currently utilized in the field of astronomical optics. The solution to the Dall-Karkham design problem is described, showing the advantage of inexpensive construction as compared with higher order surfaces. The design process reported here is a F/5 collecting system which quickly mates directly with the spectrometer; it is capable of achieving desired high resolution and sensitivity requirements. The theoretical limit of aberration tolerances is achieved with less than 1/8 of a wavelength at final focus (OPD). The design of spectrometer for ultra-violet (UV) radiation and its mechanism is included in this study.
Diode arrays fabricated by three companies have been evaluated for use in the HRS Digicon. The goal has been to optimize design and performance in the pulse counting mode. The arrays have been characterized using both photon and electron inputs. Responsivity, optical crosstalk, and a new phenomena "lead response" have been measured as a function of wavelength between 400 and 800 nm. Using pulse height analysis techniques, arrays were characterized with respect to noise and signal-to-noise ratio using low-level electron input. An attempt has been made to establish a correlation between non-intensified (photon input) and intensified (electron input) performance.
The burgeoning of the optoelectronics field, particularly fiber optics, has preceded the availability of accurate and low cost test and measurement instrumentation. With the integration of electro optics into the mainstream of electronics, it is necessary to provide the electrical engineer the same ease and accuracy of measurement that he is accustomed to with electrical parameters. Photodyne realizes this need with a broad line of field-portable but laboratory-quality instruments, whose accuracy and calibration is supported by a unique, state-of-the-art measurement system.
The physical mechanisms governing the behavior of silicon photovoltaic p-n junctions are reviewed from the point of view of using the internal quantum efficiency of such devices as absolute radiometric standards.
A project is described in which the synchrotron radiation output from the NBS storage ring known as SURF II, will be measured using a well characterized silicon based radiometer. The radiometer consists of a silicon photodiode coupled with two interference filters to restrict the spectral response to a finite and convenient spectral region for the measurement. Considerations required for the characterization of the radiometer will be discussed. The absolute radiant flux from the storage ring is also calculable from various machine parameters. A measurement of the number of circulating electrons will be derived from electron counting techniques at low levels. This will yield an important intercomparison between two entirely different determinations of the synchrotron radiant flux.
The preparation and radiometric properties of silicon detectors coated with fluorescent thin films are described. The films are deposited from solutions of clear plastics, such as acrylic resins, polyvinyl toluene or polystyrene, and of organic laser dyes in a common solvent. They are optically clear, mechanically and chemically stable, yet easily applied and removed. Multiple doped films of a few μm thickness exhibit broadband absorption from < 250 nm to ~ 450 nm and narrow band emissions with peaks ranging from 380 nm to 600 nm. Internal quantum efficiencies are close to 100 percent and fluorescence decay times are in the nanosecond range. When deposited on optically denser media, a large fraction of the fluorescent emission is trapped in the substrate. Silicon photodiodes coated with multiple doped films exhibit high external quantum efficiencies and virtually flat photon response in the near uv.
A system has been developed for measuring 1.064 µm laser pulses of about 10-15 J. The overall uncertainty of the system has been evaluated and is less than ± 15%. The details of the measurement system, its documentation relative to the NBS absolute reference calorimeters, and the associated uncertainties of measurements are discussed. Several silicon avalanche and PIN photodiodes have been evaluated. Measurements have been performed utilizing cw lasers, and laser pulses of about 30 and 200 ns. These measurements have demonstrated the feasibility of characterizing transfer standards for these low level energies by means of cw laser measurements and acousto-optic modulators. Such a system is discussed. The results of these evaluations and work towards realizing well documented transfer standards are also discussed.
This paper describes a direct measuring technique for determining the image auality of raster-scanned cathode-ray tube (CRT) displays. This technique is based on the Modulation Transfer Function (MTF) theory and human visual psychophysical data. The rationale for the technique is discussed from a theoretical as well as functional viewpoint. The instrumentation necessary to obtain these measures in manual and automatic modes is discussed. Data obtained using this measurement technique are analyzed and compared with the theoretical performance of the displays. The image quality of new CRT displays procured for the U.S. Army's Advanced Attack Helicopter is being specified and tested using this direct measuring technique.
A new method for measuring the resolution and contrast of calligraphic projection displays has been developed at NOSC (Naval Ocean Systems Center). The technique involves the use of a computer controlled photometer and a X-Y plotter. The plotter is normally used to give hard copy records of the photometric data obtained from spectral or spatial scans and subsequently stored in the memory of the controlling computer. In this application the photometric sensor, a miniature integrating sphere with a slit aperature, is mounted on the X-Y plotter pen holder which is in turn moved according to programmed instructions from the computer. With the X-Y plotter positioned vertically in front of a projection display, the projected brightness is measured and stored in the computer memory as a function of sensor position. The spatial displacement between measurements is under operator control and can be in increments as small as one thousandth of an inch. After the data is stored in the computer memory, it is then made into hard copy with the X-Y plotter in one of several plotting modes. From this hard copy the display performance parameters of resolution and contrast can be extracted. The different plotting modes are used to enhance various differences when more than one scan is recorded on the same chart.
There are many thousands of luminance photometers in the field - both telephotometers and microphotometers; however very few of these have scanning microphotometric capability. This paper describes a unique optical system that can be field-interchanged with the standard objective lens, without requiring any modification of the photometer's internal optical system, to convert an existing photometer into a high-resolution scanning microphotometer. One embodiment, called the "MicroScannerTM Spatial Scanner", will be described in detail. Used with any standard Pritchard Photometer, this scanner provides variable-speed scanning of a half-inch (12 mm) of object space with field coverage as fine as 0.0001-inches (0.0025 mm) or as broad as 0.39-inches (10 mm). The system features photometric uniformity within ± 0 5% over the entire scan distance, freedom from polarization error, and a half-inch scan distance independent of choice objective lens.
A device is described which measures the spatial profile of a laser in either the near field or far field. The laser pattern is imaged onto a pyroelectric vidicon (PEV) camera. A single frame is extracted from the camera and the image is processed using a PDP 11/20 to correct for PEV imperfections. The device will measure lasers having wavelengths of 2 µm to 10.6 µm. Detailed characteristics of the device are given.
This paper describes the relation between measurement instrumentation characteristics and the accuracy of photometric measurements of typical retroreflective materials in a photometric range. A review of the fundamental geometric and photometric terms used in the photometry of retroreflectors is presented to form a basis for discussion. The measurement method described is the method which involves determining a ratio of retroreflected light to incident light. Test instrumentation used in this measure-ment is described in terms of photometric linearity, spectral response and geometry. The instrumentation characteristics are then related to the geometric and spectral characteristics of the retroreflected light patterns from typical retroreflectors. Highly resolved observation angle curves are used to analyze errors relating to source/receptor aperture size. Entrance angle curves of various retroreflectors are used to determine goniometer accuracy requirements. The effects of rotation angle and presentation angle are illustrated by measurements on typical retroreflectors. Retroreflected spectral data is used to determine spectral fit of the photoreceptor. Effects of variability in source color temperature are presented. Instrument requirements for varying degrees of accuracy are then stated in terms of the spectral and geometric characteristics of the retroreflector to be tested.
The quality control of high efficiency antireflection coatings on contrast enhancement face plates for cathode ray tube (CRT) displays is best done spectroradiometrically. A computer controlled spectroradiometric system for measuring the reflectance of antireflection coated face plates is described and examples are given.
The evolution of absorbing surfaces for electrically calibrated radiometers, and techniques for measuring their absorptance (reflectance) are described. A new reflectometer for cavity reflectance measurements, which is based on a ring-shaped silicon photodiode, is described. The results of reflectance measurements on a series of cavities which represent the evolution of cavity technology are presented, and the significance of the results for future research are discussed.
Long path atmospheric laser transmission measurements require the precise measurement of the radiant energy of laser beams after they have been turbled by the atmosphere. This requires a detector/integrator package with very uniform response and low speckle noise. A two scatter plate device has been fabricated for use with a lmm square cryogenic infrared detector. CO2 laser measurements have been made which verify the uniformity of response and low speckle noise. Absolute accuracies of better than 1% RMS are achieved with this device. The device is augmented with a Si Diode and allows atmospheric transmission measurements to be carried out for lasers in the wavelength range of 0.6 to 11.2 microns.
The problems incurred in attempting to measure the characteristics of unique laser pulses in the nanosecond regime prior to and post - transiting an underwater propagation path are presented and discussed. The technique and equipment used to accomplish this task with emphasis on determining and recording the temporal stretching of each pulse are described and illustrated. Examples of representative measurements and records are shown.
A simple and very compact apparatus is described for obtaining the absolute efficiencies of a wide assortment of grating types and sizes. The device allows a grating to be measured in the configuration it will actually be used in, which can be particularly valuable in cases where the grating efficiency may vary significantly with the method in which it is used. Some results are given for a number of gratings.