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At least 1,207 records · Page 67

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NASA NTRS1972

Earth resources sensing technology - 24-channel multispectral sensor system development.

Description of the technology applied to a 24-channel multispectral scanner developed as a tool to investigate the portion of the electromagnetic spectrum between 0.34 and 13.0 microns. Energy reflected or emitted from the terrain and system calibration sources is collected by the scan mirror, reflected into the collecting optics, and brought to focus in a plane containing a square aperture. A dichroic optical element splits the energy which passes through the aperture into two wavelength bands in which wavelengths are greater than and less than 2.0 microns, respectively. These two wavelength bands are dispersed spectrally by two grating spectrometers. The energy from 24 distinct spectral intervals is transformed into electrical signals by 24 detector/preamplifier combinations. These signals then become the inputs to a video processor in an airborne electronics console.

Kessel, J. E.↗

NASA NTRS1972

Optical design of an imaging spectral radiometer for earth resources applications.

Description of the optics, thermal compensation measures, and calibration procedures for a scanning imaging spectroradiometer to be used in earth resources sensing applications. The spectral range covered extends from 4000 to 8500 A. Two possible modes of operation include (1) a high-spatial-resolution terrestrial survey mode with moderate spectral resolution, and (2) a high-spectral-resolution ocean survey mode with decreased spatial resolution. Two high-aperture f/1.4 objective lenses (providing fields of view of 10 and 25 deg) are interchangeable to give added flexibility in planning experiments with this instrument. A diffraction grating disperses the spectrum which is then scanned by the image sensor.

Harris, T. I.↗

NASA NTRS1972

Solar flares in the EUV observed from OSO-5.

Solar flares in three broad EUV spectral bands have been observed from OSO-5 with a grating spectrophotometer. Results are given for three large flares of Mar. 12, Mar. 21 and Apr. 21, 1969. In general, the time dependence of the flare intensity in each band is characterized by a slowly varying component with impulsive bursts superimposed. Bands 2 (465 to 630 A) and 3 (760 to 1030 A) are quite similar in their time variations, but band 1 (280 to 370 A) shows less impulsive structure, and declines more slowly. Absolute EUV intensities for the flares are estimated, and a comparison is made with the 2800 mc/sec radio emission. A flare model is proposed to account for the EUV time variations during a large flare.

Kelly, P. T.↗

NASA NTRS1972

Fluorescence spectroscopy.

Some practical aspects of the use of spectrophotofluorometers as applied to the organic analyses of returned lunar samples and other geological materials have been discussed. Because of the single beam nature of spectrophotofluorometers many instrumental artifacts such as grating anomalies, irregular spectral output of light sources and response characteristics of photodetectors are apparent in sample spectra. In order to avoid some of these instrumental artifacts from influencing sample spectra, the performance characteristics of each optical component have been described and the necessity of instrumental calibration has been emphasized.

Rho, J. H.↗

NASA NTRS1972

Electronographic cameras for space astronomy.

Magnetically-focused electronographic cameras have been under development at the Naval Research Laboratory for use in far-ultraviolet imagery and spectrography, primarily in astronomical and optical-geophysical observations from sounding rockets and space vehicles. Most of this work has been with cameras incorporating internal optics of the Schmidt or wide-field all-reflecting types. More recently, we have begun development of electronographic spectrographs incorporating an internal concave grating, operating at normal or grazing incidence. We also are developing electronographic image tubes of the conventional end-window-photo-cathode type, for far-ultraviolet imagery at the focus of a large space telescope, with image formats up to 120 mm in diameter.

Carruthers, G. R.↗

NASA NTRS1973

Removal of hydrocarbon contaminant film from spacecraft optical surfaces using a radiofrequency-excited oxygen plasma.

Results of a study on the feasibility of removing contaminant films from optical surfaces in vacuum, using an oxygen plasma, are discussed. Contaminant films were deposited onto optical surfaces from butadiene and methane gases at a pressure of about 4 torr in the presence of ultraviolet radiation. Optical surfaces evaluated included ultraviolet-reflecting mirrors, gratings, quartz disks, and spacecraft thermal control surfaces. In general, it was found that contaminants could be removed successfully from surfaces using an oxygen plasma. Exceptions were the white-paint thermal control surfaces, which, when contaminated, degraded further during exposure to the oxygen plasma.

Beverly, W. D.↗

NASA NTRS1973

High resolution rocket EUV solar spectrograph.

The design and performance of an Aerobee 150 rocket-borne solar spectrograph covering a wavelength range of 10 to 385 A are discussed. The spectrograph uses a gold-coated replica concave grating of 3-m radius with 1200 grooves/mm at an angle of incidence of 88 deg. The spectra are recorded on glass photographic plates making possible wavelength determination to 0.003 A if known standard wavelengths occur frequently enough. Special attention to scattered light made possible the photographing of the solar spectrum from 60 to 385 A without using filters to absorb the strong visible and UV sunlight, although the solar spectrum was also recorded through metal foil filters. In the laboratory the spectrograph has been used to record spectra of highly ionized metals with a resolution of 0.03 A or better.

Behring, W. E.↗

NASA NTRS1973

The EUV spectrophotometer on Atmosphere Explorer.

An extreme ultraviolet (EUV) spectrophotometer for measurements of solar radiation at wavelengths ranging from 140 to 1850 A will be included in the payload of each of the three Atmosphere-Explorer (AE) missions, AE-C, -D, and -E. The instrument consists of 24 grating monochromators, 12 of which can be telecommanded either to execute 128-step scans each covering a relatively small section of the total spectrophotometer wavelength range or to maintain fixed (command-selected) wavelength positions. The remaining 12 nonscan monochromators operate at permanently fixed wavelengths and view only a small fraction of the solar disk except for one viewing the whole sun in H Lyman alpha. Ten of the 12 scan-capable monochromators also view the entire solar disk since their primary function is to measure the total fluxes independent of the distribution of sources across the solar disk.

Hinteregger, H. E.↗

NASA NTRS1973

Remote sensing technology - The 24-channel multispectral scanner.

The multispectral scanner system installed in the NASA C-130 aircraft for use in the Earth Observations Aircraft Program constitutes a 24-channel imaging spectrometer that senses electromagnetic energy in the spectral interval from .34 to 13 microns. Energy reflected or emitted from the terrain and system calibration sources is collected by a scan mirror, reflected into collecting optics, and brought to a focus in a plane containing a 0.09 inch square aperture. A dichroic optical element splits the energy which passes through the aperture into two wavelength bands (wavelengths above and below 2 microns). These wavelength bands are then dispersed spectrally into 24 distinct spectral bands by two grating spectrometers. The spectral intervals are transformed into electrical signals by separate detector-preamplifier combinations, and the signals are used as inputs to a video processor in an airborne electronics console. System operation and performance are described.

Hayre, H. S.↗

NASA NTRS1973

Optical Signal Processing: Poisson Image Restoration and Shearing Interferometry

Optical signal processing can be performed in either digital or analog systems. Digital computers and coherent optical systems are discussed as they are used in optical signal processing. Topics include: image restoration; phase-object visualization; image contrast reversal; optical computation; image multiplexing; and fabrication of spatial filters. Digital optical data processing deals with restoration of images degraded by signal-dependent noise. When the input data of an image restoration system are the numbers of photoelectrons received from various areas of a photosensitive surface, the data are Poisson distributed with mean values proportional to the illuminance of the incoherently radiating object and background light. Optical signal processing using coherent optical systems is also discussed. Following a brief review of the pertinent details of Ronchi's diffraction grating interferometer, moire effect, carrier-frequency photography, and achromatic holography, two new shearing interferometers based on them are presented. Both interferometers can produce variable shear.

Hong, Yie-Ming↗

NASA NTRS1974

Holography utilizing surface plasmon resonances

A holographic recording medium with a substrate which has a diffraction grating composed of a number of spaced line ridges on the surface is discussed. The first layer consists of a metal with a plasma wavelength shorter than that of the selected light source. A second layer, or coating, on top of the first layer consists of a thin film of photosensitive emulsion. A diagram of the device is provided. The principles of operation are explained.

Cowan, J. J.↗

NASA NTRS1974

Ultraviolet observations of Venus from Mariner 10 - Preliminary results

An objective grating spectrometer on Mariner 10 has measured airglow in the wavelength range 200 to 1700 angstroms. The data reveal the presence of significant concentrations of hydrogen, helium, carbon, and oxygen atoms in the upper atmosphere of Venus. A preliminary analysis of the hydrogen data indicates an exospheric temperature of 400 K. There is evidence for intense airglow emission at wavelengths longward of 1350 angstroms; the nature of this emission is unclear, but the radiation is spatially extensive and detectable on both day and night sides of the planet.

Broadfoot, A. L.↗

NASA NTRS1974

Water vapor in Venus determined by airborne observations of the 8200 A band

The region of the 8200 A Band of H2O was studied in spectra of Venus obtained with an echelle grating spectrograph operated at an altitude of 14.6 km in the NASA Learjet research aircraft. Taking advantage of low foreground absorption, observing at a time of velocity quadrature, differential spectroscopy with respect to lunar spectra, and spectrum averaging, we establish a value of H2O of 3 plus or minus 20 microns for the total path over the entire disk. This value differs from earlier studies of the integrated disk but supports the low values recently derived from infrared bands and by very high spectral resolution groundbased studies.

Gull, T. R.↗

NASA NTRS1974

Four years of meteor spectra patrol

The development of the NASA-Langley Research Center meteor spectra patrol is described in general terms. The recording of very faint meteors was made possible by three great strides in optical and photographic technology in the 1960's: (1) the availability of optical-grade fused silica at modest cost, (2) the development of large transmission gratings with high blaze efficiency, and (3) the development of a method for avoiding plate fogging due to background skylight, which consisted of using a photoelectric meteor detector which actuates the spectrograph shutter when a meteor occurs in the field. The classification scheme for meteor spectra developed by Peter M. Millman is described.

Harvey, G. A.↗

NASA NTRS1974

The GSFC EUV and X-ray spectroheliograph on OSO-7

The Goddard Space Flight Center instrument carried on the pointed section of the OSO-7 satellite is described. This instrument contains: an extreme-ultraviolet spectroheliograph using glancing incidence optics of Wolter's Type II to focus the sun's light on the entrance slit of a concave grating spectrometer; an auxiliary H-alpha system; two X-ray spectroheliographs using mechanical collimators for spatial resolution and Ross filters to isolate spectral bands of interest; and a flare polarimeter operating in the 15-40 keV X-ray region. The subsystems may be operated in a number of modes which, when combined with the spacecraft modes, give the instrument great flexibility for making solar observations. Representative results from each of the subsystems are presented.

Underwood, J. H.↗

NASA NTRS1974

Mathematical operations by optical processing

Some recent developments in coherent optical processing are described in this paper. Specifically, the use of one or more elementary gratings to perform useful processing operations and computer-generated spatial filters to obtain generalized transforms are discussed. Applications incorporating nonlinear optical elements and optical feedback into the processing system are also presented.

Lee, S. H.↗

NASA NTRS1974

Solar-flare emission lines in the range from 66 to 171 A; 2sr 2pk - 2s/r-1/ 2p/k+1/ transitions in highly ionized iron

New emission lines found in several flare spectra obtained with the Goddard grating spectrometer on the OSO-5 satellite, in 1969, have been listed by wavelength and relative intensity. These new lines, including several as strong as normal quiet-sun lines, are extremely variable in intensity and have been assigned mainly to transitions of the type 2sr 2pk - 2s(r-1) 2p(k+1) in iron ions up to Fe XXIII.

Kastner, S. O.↗

NASA NTRS1974

LST and supporting technology

In order to realize the LST objectives of high angular resolution, extended wavelength coverage and faint object detection, the performance of the instruments must be matched to that of the telescope. To insure that adequate technology is available by 1976, an intensive SR & T program has been initiated which builds on previous work and is coordinated with work in other agencies. The primary areas of concern are detectors, on-board computers, and ultraviolet optical components. In the last area grating work is being emphasized. The on-board computer will be necessary to allow pre-processing of raw data and enable detector operation in a pulse counting mode. For detectors, the SEC Vidicon development will be continued but the use of solid-state arrays in the electron bombarded mode and channel plate detectors are being seriously considered. One challenging problem is to provide 2 K cooling to permit ultra-sensitive IR observations to be made.

Sobieski, S.↗