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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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In this correspondence maximum-likelihood binary detection theory is applied to an incoherent optical system model employing photodetectors governed by Laguerre counting statistics. It is shown that a maximum-likelihood Laguerre detector corresponds to a count comparison over each signaling interval. Laguerre error probabilities are presented and compared with those for Poisson counting.
The design, development and operation are described of the laser communications system developed for potential space shuttle application. A brief study was conducted to identify the need, if any, for narrow bandwidth space-to-space communication on the shuttle vehicles. None have been specifically identified that could not be accommodated with existing equipments. The key technical features developed in this hardware are the conically scanned tracker for optimized track while communicating with a single detector, and the utilization of a common optical carrier frequency for both transmission and detection. This latter feature permits a multiple access capability so that several transceivers can communicate with one another. The conically scanned tracker technique allows the received signal energy to be efficiently divided between the tracking and communications functions within a common detector.
A study was made to evaluate the potential for remote ground-based measurement of upper atmospheric ozone by determining the absorption ratio of selected narrow bands of sunlight as reflected by satellites while passing into eclipse, using the NASA Mobile Satellite Photometric Observatory (MOSPO). Equipment modifications to provide optimum performance were analyzed and recommendations were made for improvements to the system to accomplish this. These included new sensor tubes, pulse counting detection circuitry, filters, beam splitters and associated optical revision, along with an automatic tracking capability plus corresponding operational techniques which should extend the overall measurement capability to include use of satellites down to 5th magnitude.
Sco X-1 was monitored at optical and X-ray wavelengths from 1970 April 26 to 1970 May 21. The optical observations were made at six observatories around the world and the X-ray observations were made by the Vela satellites. There was a tendency for the object to show greater variability in X-ray when the object is optically bright. A discussion of the intensity histograms is presented for both the optical and X-ray observations. No evidence for optical or X-ray periodicity was detected.
Optically-selective, acoustically-resonant, gas-detecting device is used to measure intensity of radiation-induced pressure variations. Use of diaphragm improves sensitivity and immunity to background noise.
Visual photometric function data for Saturn's rings were analyzed in terms of elementary anisotropic scattering radiative transfer models which involve the Henyey-Greenstein function. Limits were placed on the combinations of single scattering albedo, and backscattering directivity, which are permitted by observation. Particles with lunar-like scattering properties were excluded by the analysis. Results are consistent with the ring particles being more-or-less pure, and spherical, conglomerates of H2O frost. Multicolor (5500 A-7600 A), narrow band (100 A), area scanning photometry was used to study the wavelength variation in the optical appearance of Uranus. Limb brightening was detected in two CH4 bands, i.e. 6190A and 7300A. Spectrophotometric observations and analysis of the asteroids and Raman spectroscopy of the atmosphere of Uranus are also briefly discussed.
Sensitive, relatively inexpensive instrument uses phase-detection techniques to sense presence of objects. Phase-sensitive detectors, LED, photodiode with response matched to LED output, and filtering lens allow detector to operate over narrow radiation band, giving selectivity over stray light.
An active optical technique (differential absorption lidar (DIAL)) for detecting, ranging, and quantifying the concentration of anhydrous HCl contained in the ground cloud emitted by solid rocket motors (SRM) is evaluated. Results are presented of an experiment in which absorption coefficients of HCl were measured for several deuterium fluoride (DF) laser transitions demonstrating for the first time that a close overlap exists between the 2-1 P(3) vibrational transition of the DF laser and the 1-0 P(6) absorption line of HCl, with an absorption coefficient of 5.64 (atm-cm) to the -1 power. These measurements show that the DF laser can be an appropriate radiation source for detecting HCl in a DIAL technique. Development of a mathematical computer model to predict the sensitivity of DIAL for detecting anhydrous HCl in the ground cloud is outlined, and results that assume a commercially available DF laser as the radiation source are presented.
In some of the more difficult applications of laser Doppler velocimetry such as in combustion research, transonic flow, transverse wind, and others, the optical signals are too small for classical detection methods. This paper summarizes the theory, experimental prototype hardware, and test results for a new type of high-speed photon-correlation signal processor which is being developed for weak laser velocimeter signals and other photon-resolved signals. The new system may also be considered to be a statistical digital frequency discriminator. It uses full multiplication with 10-nsec delay time and has the potential for extension to the measurement of the velocity correlations and spectra.
The Galileo satellite program includes the delivery of an entry probe to the Jovian equatorial atmosphere in mid-1985. Optical and RF sensors for a lightning detection system are included as a part of the probe experimental payload. In this paper, calculations of the RF wave propagation and reflection characteristics of the equatorial Jovian atmosphere and ionosphere for frequencies less than 100 kHz are presented. It is shown that wave propagation is limited to line-of-sight and one-hop from the ionosphere. Results are also presented of a statistical treatment of the RF wave power densities for the case of a finite number of events and for the case of a uniformly distributed source. The results can be applied to specific RF experiment configurations concerned with establishing the statistical characteristics of Jovian lightning.
A report is presented of experimental results on picosecond time-resolved photoacoustic measurements of excited-state lifetimes, cross sections, and polarization properties for organic dye molecules in solution, using a new technique in which the total photoacoustic impulse produced by two ultrashort optical pulses with variable time delay between them is detected. The picosecond photoacoustic detection technique reported here appears to be a promising new way to observe weak excited-state cross sections and to perform picosecond lifetime measurements in a large variety of weakly absorbing and/or nonfluorescing atomic and molecular systems.
Using precise positions from the HEAO 1 Scanning Modulation Collimator experiment, two hard X-ray sources, 4U 0728 - 25 = 3A 0726 - 260 and 4U 2206 + 54 = 3A 2206 + 543, are identified with early-type stars. In both cases broad (10 A FWHM) H-alpha emission is detected. The UBV colors suggest that the optical counterparts are main-sequence B0-B2 stars at 2-6 kpc, implying a mean X-ray luminosity of order 10 to the 35th ergs/sq cm s (2-10 keV). The X-ray emission in both cases is highly variable, and it is suggested that they belong to the class of X-ray emitting Be stars, containing a neutron star in a widely separated binary system.
An experimental system for the detection of three dimensional acoustic fields in optically transparent media using a dual beam differential interferometer is described. In this system, two coherent, parallel, focused laser beams are passed through the specimen and the interference fringe pattern which results when these beams are combined shifts linearly by an amount which is related to the optical pathlength difference between the two beams. It is shown that for small signals, the detector output is directly proportional to the amplitude of the acoustic field integrated along the optical beam path through the specimen. A water tank and motorized optical platform were constructed to allow these dual beams to be scanned through an ultrasonic field generated by a piezoelectric transducer at various distances from the transducer. Scan data for the near, Fresnel, and far zones of a uniform, circular transducer are presented and an algorithm for constructing the radial field profile from this integrated optical data, assuming cylindrical symmetry, is described.
Laser anemometry offers a nonintrusive means for obtaining flow field information. Current research at NASA Lewis Research Center is focused on instrumenting a warm turbine facility with a laser anemometer system. In an effort to determine the laser anemometer system best qualified for the warm turbine environment, the performance of a conventional laser fringe anemometer and a two spot time of flight system were compared with a new, modified time of flight system, called a Four Spot laser anemometer. The comparison measurements were made in highly turbulent flows near walls. The Four Spot anemometer uses elliptical spots to increase the flow acceptance angle to be comparable to that of a Laser Fringe Anemometer. Also, the Four Spot uses an optical code that vastly simplifies the pulse detection processor. The results of the comparison measurements will exemplify which laser anemometer system is best suited to the hostile environment typically encountered in warm rotating turbomachinery.
Laser anemometry offers a nonintrusive means for obtaining flow field information. Current research at NASA Lewis Research Center is focused on instrumenting a warm turbine facility with a laser anemometer system. In an effort to determine the laser anemometer system best qualified for the warm turbine environment, the performance of a conventional laser fringe anemometer and a two spot time of flight system were compared with a new, modified time of flight system, called a Four Spot laser anemometer. The comparison measurements were made in highly turbulent flows near walls. The Four Spot anemometer uses elliptical spots to increase the flow acceptance angle to be comparable to that of a Laser Fringe Anemometer. Also, the Four Spot uses an optical code that vastly simplifies the pulse detection processor. The results of the comparison measurements will exemplify which laser anemometer system is best suited to the hostile environment typically encountered in warm rotating turbomachinery.
A number of optical design and technology challenges are discussed with reference to specific space optics projects. The projects examined include the Large Deployable Reflector, multiple-mirror telescopes, the Hubble Space Telescope, and the Circumstellar Imaging Telescope. Other projects discussed include a voyage to a distance of 1000 astronomical units, the Shuttle Imaging Spectrometer Experiment, and directional optical systems. The ultimate challenge is the detection of and communication with any planets that may be discovered around nearby stars.
Researchers observed the nuclear regions of the galaxies NGC 2146 and IC 342 in CO-12 and CO-13 J=1-0 and J=2-1 lines using the Five College Radio Astronomy Observatory (FCRAO) 14m telescope. NGC 2146 is a peculiar Sab spiral galaxy. Its complex optical morphology and strong nuclear radio continuum emission suggest that it is experiencing a phase of violent activity and could have a polar ring which may have resulted from an interaction. IC 342 is a nearby luminous Scd spiral galaxy. Strong CO, infrared and radio continuum emission from the nuclear region of IC 342 indicate enhanced star-forming activity, and interferometric CO-12 J=1-0 observations reveal a bar-like structure centered on the nucleus, along the dark lane in the NS direction. These two galaxies are selected based on their different dust temperatures and star formation efficiencies (SFE) as derived from the Infrared Astronomy Satellite (IRAS) S sub 60 mu/S sub 100 mu flux density ratio and L sub IR/M(H2), respectively, with a relatively high SFE and dust temperature of 45 K in NGC 2146 and a relatively low SFE and dust temperature of 35 K in IC 342. The data from the different CO-12 and CO-13 lines are used to study the physical conditions in the molecular clouds in the galaxies. Researchers also consider the radiative transfer to determine whether a warm and optically thin gas component exists in these galaxies, as has been suggested in the case of M82 (Knapp et al. 1980), and whether the warm gas is related to the dust properties. Since optically thin CO-12 gas is rarely detected in our own Galaxy (except in outflow sources), to confirm its existence in external galaxies is very important in understanding the molecular content of external galaxies and its relationship to star formation activity. The present CO-12 J=2-1 and CO-13 J=2-1 and J=1-0 data for NGC 2146 are the first detections of this galaxy to our knowledge. The CO-12 J=1-0 distribution in NGC 2146 has been measured as part of the FCRAO Extragalactic Survey. For the well-studied IC 342, the data are compared with 30m observations and other available data. Researchers present the observed results.
The use of satellite remote sensing is reviewed with respect to the investigation of polar regions and global meteorological processes. Data collected from previous and ongoing satellite missions sponsored by NASA and NOAA are discussed in terms of their ability to describe surface characteristics. Data relating to ocean/atmosphere heat transfer are obtained from microwave radiometers and synthetic aperture radars to give estimates of surface temperatures. Ocean color at several frequencies can be measured to estimate chlorophyll content, and optical and infrared sensors aid in the detection of short- and long-term variance in solar irradiance and earth radiation flux. The geophysical variables collected from satellite data at high latitudes can be used to understand the global climate, atmospheric warming, and other significant mechanisms.