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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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NASA NTRS1984

NIMBUS-7 CZCS. Coastal Zone Color Scanner Imagery for Selected Coastal Regions. North America - Europe. South America - Africa - Antarctica. Level 2 Photographic Product

The Nimbus-7 Coastal Zone Color Scanner (CZCS) is the first spacecraft instrument devoted to the measurement of ocean color. Although instruments on other satellites have sensed ocean color, their spectral bands, spatial resolution, and dynamic range were optimized for geographical or meteorological use. In the CZCS, every parameter is optimized for use over water to the exclusion of any other type of sensing. The signal-to-noise ratios in the spectral channels sensing reflected solar radiance are higher than those required in the past. These ratios need to be high because the ocean is such a poor reflecting surface that the majority of the signal seen by the reflected energy channels at spacecraft altitudes is backscattered solar radiation from the atmosphere rather than reflected solar energy from the ocean. The CZCS is a conventional multichannel scanning radiometer utilizing a rotating plane mirror at a 45 deg angle to the optic axis of a Cassegrain telescope. The mirror scans 360 deg; however, only 80 deg of data centered on the spacecraft nadir is collected for ocean color measurements. Spatial resolution at spacecraft nadir is 825x825 m with some degradation at the edges of the scan swath. The useful swath width from a spacecraft altitude of 955 km is 1600 km.

Source record↗

NASA NTRS1986

A dual plate thermoplastic recording device for holographic interferometry

The development of a dual plate holographic interferometer using thermoplastic recording devices is described. The operational characteristics of the thermoplastic devices are investigated and optimized for fringe contrast and signal-to-noise ratio. The dual plate device was demonstrated in a transonic wind tunnel at NASA Ames Research Center. The interferograms derived from the thermoplastic device are compared with those derived from conventional photographic emulsions. The fringe contrast achieved with the optimized thermoplastic device is equivalent to the contrast achieved with conventional techniques.

Umstatter, Holly L.↗

NASA NTRS1987

Radio observations of carbon monoxide toward Zeta Ophiuchi - Velocity structure, isotopic abundances, and physical properties

This paper presents a small-scale map of the molecular gas around the line of sight toward Zeta Oph made with measurements of the (C-12)O (1-0) emission obtained at high signal-to-noise ratio and high velocity resolution. In addition, a measurement of the (C-12)O (2-1) line emission and a detection of (C-13)O along the line of sight to the star are reported. The results show that the CO emission toward the star is composed from at least four components with peak velocities at -2.0, -0.7, 0.0, and +0.6 km/s. The radio observations yield a total CO column density of 1.4 x 10 to the 15th/sq cm, with about one-half of the total CO column density being in the main component at -0.7 km/s. The main cmponent is uniform over the map, but the other components are variable, suggesting that the cloud is clumpy. The data on the two CO transitions imply that the excitation temperature and the density of the main component are about 7 K and 800/cu cm, respectively.

Langer, William D.↗

NASA NTRS1988

Generalized minimum shift-keying modulation techniques

The simultaneous data demodulation and phase tracking of an MSK signal using the Viterbi algorithm is described and two variations of MSK modulation are studied. The MSK with overlay is a dual rate modulation technique where low-and high-rate data are superimposed on an MSK signal. Here the demodulator uses the Viterbi algorithm to estimate both the low-and high-rate data simultaneously. The MSK with pseudorandom sequence spreading combats intentional or unintentional jamming. A simplified receiver for these spread spectrum MSK signals is found, which takes into consideration the effect of random phase perturbations. The performance of these demodulators is evaluated using transfer function bounds for the bit error probability. It is shown that with a reasonable short overlay period, at a relatively high signal-to-noise ratio (13 dB), there is a small (0.7 dB) loss of performance. For demodulation of the spread spectrum MSK signal, a simplified receiver is derived, and its performance in the presence of continuous jamming is evaluated.

Sadr, Ramin↗

NASA NTRS1988

Systematic aspects of direct extrasolar planet detection

Using the first optical observatory in space, the Hubble Space Telescope, images of possible extrasolar planets will have poor contrast against the background of diffracted and scattered starlight. The very long exposure time required to achieve an adequate signal-to-noise ratio will make their detection infeasible. For a future telescope, a 16-fold increase in either the smoothness of the collecting area of the optics would reduce the exposure time to a tolerable value, but the contrast would remain low and the required photometric precision high. In this situation, the feasibility of detection would be contingent on the careful identification and control of systematic errors.

Brown, Robert A.↗

NASA NTRS1988

Helioseismology from the South Pole: Comparison of 1987 and 1981 Results

Full disk images with 10 arc sec pixels and filtered to a 7 A pass band centered on the Ca II K line were obtained from the geographic South Pole in 1981 and 1987. In 1981, 50hr of essentially uninterrupted data were obtained. In 1987, three such runs were obtained over a period of 325 hours for a duty cycle of 47 percent. The 1987 observations are characterized by a much lower level of solar activity than 1981, a much improved CCD camera, considerably better image stability and a varying amount of instrumental scatter. The 1987 data have a substantially better signal-to-noise ratio than the 1981 data so that oscillations with degrees from 0 to 150 and frequencies from 2 to 7 mHz are well observed. The observations were reduced to spectra in l, m, and v. A comparison of p-mode frequencies measured in 1981 and 1987, and coefficients of Legendre polynomial expansions of frequency shifts caused by solar rotation are presented. The time behavior of systematic frequency shifts which depend upon m but which do not arise from rotation is described.

Jefferies, S. M.↗

NASA NTRS1988

Airborne imaging spectrometer-2 - Radiometric spectral characteristics and comparison of ways to compensate for the atmosphere

The reduction of AIS data to spectral radiance utilizing the detector responsivity equations developed by a laboratory calibration of the instrument with a BaSO4-coated integrating sphere is described. Estimates of the signal-to-noise ratio for laboratory and flight conditions are obtained. In addition, the effective in-flight instrumental spectral sampling interval is estimated by using atmospheric CO2 absorption lines generated from LOWTRAN simulations.

Conel, James E.↗

NASA NTRS1987

HIRIS - EOS instrument with high spectral and spatial resolution

The High-Resolution Imaging Spectrometer (HIRIS) is designed for NASA's Earth Observing System (EOS). It will have 10-nm wide spectral bands from 0.4-2.5 microns at 30 m spatial resolution over a 30 km swath. The spectral resolution allows identification of many minerals in rocks and soils, important algal pigments in oceans and inland waters, spectral changes associated with plant canopy biochemistry, composition of atmospheric aerosols, and grain size of snow and contamination by absorbing impurities. The bands will have 12-bit quantization over a dynamic range suitable for bright targets, such as snow. For targets of low brightness, such as water bodies, image-motion compensation will allow gains up to a factor of 8 to increase signal-to-noise ratios. The sensor will be able to point + or - 24 deg crosstrack and +60/-30 deg downtrack. In the 824-km orbit altitude proposed for EOS, the crosstrack pointing capability will allow 4-5 views during a 16-day revisit cycle.

Dozier, Jeff↗

NASA NTRS1988

HIRIS - The High Resolution Imaging Spectrometer

The High-Resolution Imaging Spectrometer (HIRIS) is a JPL facility instrument designed for NASA's Earth Observing System (Eos).It will have 10-nm wide spectral bands from 0.4-2.5 microns at 30 m spatial resolution over a 30 km swath. The spectral resolution allows identification of many minerals in rocks and soils, important algal pigments in oceans and inland waters, spectral changes associated with plant canopy biochemistry, composition of atmospheric aerosols, and grain size of snow and its contamination by absorbing impurities. The bands wil have 12-bit quantization over a dynamic range suitable for bright targets, such as snow. For targets of low brightness, such as water bodies, image-motion compensation will allow gains up to a factor of eight to increase signal-to-noise ratios. In the 824-km orbit altitude proposed for Eos, the crosstrack pointing capability will allow 4-5 views during a 16-day revisit cycle.

Dozier, Jeff↗

NASA NTRS1988

1.3-micron Ku-band fiberoptic transmission system for satellite communications and antenna remoting

Microwave fiberoptic transmission system provides numerous advantages for satellite communications terminals and antenna remoting. This paper described a 1.3-micron, 6-15 GHz, 1-km fiberoptic system design and performance. The microwave characteristics of the laser diode photodetector are discussed in detail. The preliminary measured system signal-to-noise ratio (SNR) are 110-120 dB/Hz in the frequency range of 6-15 GHz. A 20 to 30 dB SNR improvement is achievable when coherent detection and PD impedance matching are employed.

Pan, J. J.↗

NASA NTRS1993

Performance results of a digital test signal generator

Performance results of a digital test signal-generator hardware-demonstration unit are reported. Capabilities available include baseband and intermediate frequency (IF) spectrum generation, for which test results are provided. Repeatability in the setting of a given signal-to-noise ratio (SNR) when a baseband or an IF spectrum is being generated ranges from 0.01 dB at high SNR's or high data rates to 0.3 dB at low data rates or low SNR's. Baseband symbol SNR and carrier SNR (Pc/No) accuracies of 0.1 dB were verified with the built-in statistics circuitry. At low SNR's that accuracy remains to be fully verified. These results were confirmed with measurements from a demodulator synchronizer assembly for the baseband spectrum generation, and with a digital receiver (Pioneer 10 receiver) for the IF spectrum generation.

Gutierrez-Luaces, B. O.↗

NASA NTRS1993

Calibration of the receiver channel for the GOPEX precursor experiments

Calibration measurements for the cooled (253 K) photomultiplier tube (PMT) detector, used on the receiver channel of the transmit/receive (T/R) switch for GOPEX, were conducted in the laboratory. A pulsed frequency-doubled neodymium:yttrium-aluminum-garnet (Nd:YAG) laser was used to direct 532-mn light on the PMT. By monitoring the energy per pulse of the light incident on the PMT, the minimum number of photons detected could be determined. These results agreed with the photon flux back-calculated from the PMT output waveform. Approximately 700 incident photons arriving during a temporal pulse width of approximately 65 nsec were detected with a signal-to-noise ratio (SNR) of approximately 1. Other receiver channel characteristics, such as PMT dark currents, optical transmission, and interference filter sensitivity to angle of light incidence, were also measured.

Biswas, A.↗

NASA NTRS1961

Project Echo: System Calculations

The primary experimental objective of Project Echo was the transmission of radio communications between points on the earth by reflection from the balloon satellite. This paper describes system calculations made in preparation for the experiment and their adaptation to the problem of interpreting the results. The calculations include path loss computations, expected audio signal-to-noise ratios, and received signal strength based on orbital parameters.

Ruthroff, Clyde L.↗

NASA NTRS1961

Project Echo: FM Demodulators with Negative Feedback

The primary experimental objective of Project Echo was the transmission of radio communications between points on the earth by reflection from the balloon satellite. Owing to the large path losses from transmitter to receiver via the satellite, a wide-band frequency modulation technique was used in which bandwidth was traded for signal-to-noise ratio. This paper describes the FM receiving demodulators employed. Negative feedback applied to the local oscillator reduces the FM modulation index in the receiver IF amplifiers, resulting in threshold performance superior to that of conventional FM receivers.

Ruthroff, Clyde L.↗

NASA NTRSDate not supplied

The Aeolus-Earth DWTS Heliophysics Mission

The Aeolus-Earth Mission (DWTS-Helio) is a recently selected NASA Heliophysics investigation that will apply the innovative Doppler Wind Temperature Sounder (DWTS) technique to the Space Atmosphere Interaction Region (SAIR) at ~105-180 km. The technique, invented by Gordley & Marshall (2011), applies the Doppler Scanning with Gas Filter (DSGF) technique using a cryo-cooled MWIR radiometer to view the limb of the atmosphere from LEO (orbital velocity creates the Doppler shifts required by the technique). For this implementation of DWTS, a Nitric Oxide (NO) low pressure gas cell is used. The limb of the atmosphere is observed from a spacecraft at orbital velocity, and as an observed air volume passes through the field of view, this velocity creates a set of Doppler-shifted images. These images are used to create Doppler Integrated Pass (DIP) signals, from which atmospheric temperature and wind profiles are extracted (it may be considered a converse of the successful in-flight calibration of gas cells used for the HALOE instrument). The technique is relative, removing the need for absolute radiances, and the signal-to-noise ratio for this technique is high, resulting in good measurement precision. Different gas cells can be used to create different altitude coverage and may be combined to measure a more continuous altitude range. For example, using a NO cell captures the lower atmosphere from 30-50km as well as the SAIR, while using the 13 isotopologue of CO2 would capture 50-120km. Due to the desired data volume as well as power and thermal considerations, this initial Aeolus-Earth flight will be more suited for a ‘hosted’ payload on an Orbital Maneuvering Vehicle platform instead of the ‘free-flyer’ option originally investigated. Lastly, the technique is sufficiently powerful that a two-channel system could produce full Mars atmosphere data not currently possible.

DWTS↗

NASA NTRS1973

Feasibility test of a solid state spin-scan photo-imaging system

The feasibility of using a solid-state photo-imaging system to obtain resolution imagery from a Pioneer-type spinning spacecraft in future exploratory missions to the outer planets is discussed. Evaluation of the photo-imaging system performance, based on electrical video signal analysis recorded on magnetic tape, shows that the signal-to-noise (S/N) ratios obtained at low spatial frequencies exceed the anticipated performance and that measured modulation transfer functions exhibited some degradation in comparison with the estimated values, primarily owing to the difficulty in obtaining a precise focus of the optical system in the laboratory with the test patterns in close proximity to the objective lens. A preliminary flight model design of the photo-imaging system is developed based on the use of currently available phototransistor arrays. Image quality estimates that will be obtained are presented in terms of S/N ratios and spatial resolution for the various planets and satellites. Parametric design tradeoffs are also defined.

Laverty, N. P.↗

NASA NTRS1978

Digital set point control of nonlinear stochastic systems

A technique for digital control of nonlinear stochastic plants is presented. The development achieves a practical digital algorithm with which the closed-loop system behaves in a classical Type I manner even with gross nonlinearities in the plant structure and low signal-to-noise power ratios. The design procedure is explained in detail and illustrated by an example whose simulated responses testify to the practicality of the approach.

Moose, R. L.↗

NASA NTRS1978

Passive imaging through the turbulent atmosphere - Fundamental limits on the spatial frequency resolution of a rotational shearing interferometer

The signal-to-noise (S/N) ratio to be expected when a 180 deg rotationally shearing interferometer is used for image recovery at the diffraction limit of a large telescope is computed. The variance and covariance of the irradiance fluctuations at the detector array are shown to yield measures of the high-frequency spatial spectrum of the source. Four fundamental sources of noise are considered: temporal fluctuations of the source, space-time fluctuations of the atmosphere, shot noise in the detected photocurrents, and the effects of finite sampling. S/N is found to be directly proportional to the angular resolution of the telescope, the single-frame integration time, the square root of the number of frames, the cube of the operating wavelength, the quantum efficiency of the detector, and the average spectral irradiance from the source on the pupil. It is inversely proportional to the cube of the field angle subtended by the source (or part thereof) under study.

Burke, J. J.↗