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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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At least 505 records · Page 28
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NASA NTRS1985

A Preliminary Evaluation of LANDSAT-4 Thematic Mapper Data for Their Geometric and Radiometric Accuracies

Some LANDSAT thematic mapper data collected over the eastern United States were analyzed for their whole scene geometric accuracy, band to band registration and radiometric accuracy. Band ratio images were created for a part of one scene in order to assess the capability of mapping geologic units with contrasting spectral properties. Systematic errors were found in the geometric accuracy of whole scenes, part of which were attributable to the film writing device used to record the images of film. Band to band registration showed that bands 1 through 4 were registered to within one pixel. Likewise, bands 5 and 7 also were registered to within one pixel. However, bands 5 and 7 were misregistered with bands 1 through 4 by 1 to 2 pixels. Band 6 was misregistered by 4 pixels to bands 1 through 4. Radiometric analysis indicated two kinds of banding, a modulo-16 stripping and an alternate light dark group of 16 scanlines. A color ratio composite image consisting of TM band ratios 3/4, 5/2, and 5/7 showed limonitic clay rich soils, limonitic clay poor soils, and nonlimonitic materials as distinctly different colors on the image.

Podwysocki, M. H.↗
NASA NTRS1985

Vector magnetic field observations with the Haleakala polarimeter

Several enhancements were recently made to the Haleakala polarimeter. Linear array detectors provide simultaneous resolution over a 3-A wavelength range, with spectral resolution of 40 mA. Optical fibers are now used to carry the intensity-modulated light from the rotating quarter-wave plate polarimeter to the echelle spectrometer, permitting its removal from the spar to a more stable environment. These changes, together with improved quarter-wave plates, reduced systematic errors to a few parts in 10,000 for routine observations. Examples of Stokes profiles and derived magnetic field maps are presented.

Mickey, D. L.↗
NASA NTRS1985

The vector magnetograph of the Sayan Solar Observatory

The problem of choosing an optimum scheme for the electrooptical analyzer of polarization and related control principles are discussed. An electrooptical deflector, which is advantageously used to employ a single photodetector and to remove systematic errors inherent in magnetographs with two photodetectors in the wings of the line is discussed, as well as adjustment errors of optical elements of the polarization analyzer and errors of control voltages. A method for measuring the telescope's polarization matrix, reduction of magnetographic measurements for instrumental polarization and calibration of magnetograph channels are examined. Questions of evaluating scattered light and of reducing magnetic field measurements are also considered as a computational procedure for the magnetic field vector parameters is briefly outlined. Computer control of the solar magnetograph and of the processing and control system software is discussed.

Grigoryev, V. M.↗
NASA NTRS1985

Absolute rigidity spectrum of protons and helium nuclei above 10 GV/c

Proton and helium nuclei differential spectra were gathered with a balloon borne magnet spectrometer. The data were fitted to the assumption that the differential flux can be represented by a power law in rigidity. In the rigidity range 10 to 25 GV/c the spectral indices were found to be -(2.74 plus or minus 0.04) for protons and -(2.71 plus or minus 0.05) for helium nuclei. A brief discussion is given by systematic errors.

Golden, R. L.↗
NASA NTRS1984

Kinetics of the reaction O + ClO yields Cl + O2

The kinetics of the reaction O + ClO yields Cl + O2 (k1) were studied by using resonance fluorescence to monitor the decay of O atoms which had been generated from the laser photolysis of ClO. A discharge flow system was used to generate the ClO and its concentration was measured directly by multipass absorption spectrometry. The results are k1(298) = (4.2 + or -0.8) x 10 to the -11th cu cm/s (including systematic errors) with E/R determined to lie in the range + or - 200 K. The literature data are reviewed and a composite value of k1(T) = 6.0 x 10 to the -11th exp-(100/T) is recommended for stratospheric modeling calculations. The atmospheric implications of the revised rate constant are discussed briefly.

Margitan, J. J.↗
NASA NTRS1985

Interfacial tension of fluids near critical points and two-scale-factor universality

Measurements of interfacial tension in the critical region of a wide variety of fluids are reviewed. The data are analyzed using theoretical values of the critical exponents to obtain amplitude ratios. Many of the data are consistent within a few percent of sigma(0). Comparison of these amplitude ratios with ratios from a field-theory calculation and from a simulation suggests that the theoretical values are about half the experimental ones. Systematic errors which are the source of this discrepancy are discussed. The data sources and processing procedures of this study are also discussed, pointing out that for liquid-vapor systems the capillary length often has a remarkably simple temperature dependence.

Moldover, M. R.↗
NASA NTRS1984

Kinetics of the reaction Cl + NO2 + M

Using atomic chlorine resonance fluorescence at 140 nm to detect the decay of atomic chlorine in the presence of an excess of NO2, the rate constant for the reaction Cl + NO2 + M, where M is the total gas concentration, is measured over the temperature range 264 to 417 K and at a pressure 1 to 7 torr in a discharge flow system. The rate constants for M= He and M= N2 are measured and the results are summarized in a table. The systematic error of the rate constants is estimated to be about 15 percent. A static photolysis system coupled with an FTIR spectrophotometer is used to determine the branching ratio for the formation of two possible isomers. The ratio is concluded to be ClONO (greater than or equal 75 percent) and ClNO2 (less than or equal 25 percent) which is in agreement with the results of Niki et al. (1978).

Leu, M.-T.↗
NASA NTRS1985

The rotation period and pole orientation of asteroid 4 Vesta

In 1971 asteroid Vesta was observed in a region of the sky in which it had never been observed before. Its photometric lightcurve had two distinct maxima. Those observations have been the only strong evidence to support a rotation period of about 10 hr 41 min. Lightcurves made in 1982, when Vesta was at the same aspect as 1971, do not show two different maxima. It is concluded that there was a systematic error in the 1971 observations. At this time a definitive statement cannot be made about the true period of Vesta, although the 5 hr 20 min period does appear more plausible. Radar echoes in 1988 and 1992 should resolve the problem. The shorter rotation period was assumed and the photometric astrometry method applied. The sidereal period is 5 hr 20 min 31.68 sec (0.2225889 + or 0.0000002 days), the rotation is prograde, and the coordinates of the north pole are 103 deg longitude and + 43 deg latitude with an uncertainty of about 6 deg.

Taylor, R. C.↗
NASA NTRS1985

Precision geodesy using the Mark-III very-long-baseline interferometer system

Very-long-baseline interferometry (VLBI) has been used to make precise measurements of the vector separation between widely separated antennas. The system for acquiring and processing VLBI data known as Mark-III is described. Tests of the system show it to have millimeter-level accuracy on short baselines; measurements of baselines longer than a few hundred kilometers suggest that accuracy is limited by the uncertainty in the calibration of tropospheric path delay to the level of a few centimeters. VLBI experiments conducted between 1976 and 1983 have demonstrated the stability of the North American plate by showing that there is no change in the distance between eastern California and Massachusetts at the level of a few millimeters per year or greater. Experiments made from 1980 to 1984 indicate that the distance from Massachusetts to Sweden is increasing by 1.7 + or - 1 cm/year where the quoted standard deviation includes the estimated effects of systematic errors.

Clark, T. A.↗
NASA NTRS1985

Middle Atmosphere Tides at Christchurch (44 Deg S, 17 Deg E) in November 1981 and May 1982

Atmospheric tides at Christchurch were measured at heights of 80 to 100 km, in 2.5 km intervals during the ATMAP campaigns of November 1981 and May 1982. Average components for the 5-day periods, November 19 to 23 and May 3 to 7, were extracted by making an equally weighted least squares fit to the hourly mean values, using the sum of mean, diurnal and semidiurnal terms. Estimates of standard deviation from the least squares fit tend to be less than the variability between successive 5-day samples, but 5 to 8 ms(-1) and 2 to 3 h are typical. At altitudes below 83 km there may be gaps of up to 6 hours during the night which may generate a systematic error in the components. Amplitude and phase characteristics are generally consistent with November 1980 and 1982 and May 1981, although the amplitude of the diurnal EW tide was low in November 1981, with consequent large phase fluctuations.

Fraser, G. J.↗
NASA NTRS1985

Ostwald ripening theory

An approximate analytical technique for extracting the concentration dependence of the interdiffusion coefficient was derived from diffusion measurements carried out with the diaphragm cell. The systematic error incurred in using the technique was estimated and found to be no greater than the random error ordinarily encountered in these experiments.

Baird, J. K.↗
NASA NTRS1986

Total ionospheric electron content calibration using SERIES GPS satellite data

The current status of the Deep Space Network advanced systems research into ionospheric calibration techniques, based on Global Positioning System (GPS) data is described. A GPS-based calibration system is planned to replace the currently used Faraday rotation method by 1989. The SERIES receiver system determines the differential group delay of signals transmitted at two different carrier frequencies. This differential delay includes an ionospheric component and a GPS transmitter offset. The transmitter offsets are different for each GPS satellite. Tests were conducted to assess the effect of the offsets on the ionospheric calibration accuracy. From the obtained data, the total electron content and GPS transmitter offsets are calculated by a least squares estimation method employing a local model of total ionospheric electron content. The end product is an estimation of the total ionospheric content for an arbitrary line-of-sight direction. For the presented polynomial fitting technique, the systematic error due to mismodeling is estimated to be approximately 6 x 10 to the 16th power el/sq m, while the formal error is approximately 2 x 10 to the 16th power el/sq m. The final goal is an error of 3 x 10 to the 16th power el/sq m (approximately 0.7 ns at 2.3 GHz).

Lanyi, G.↗
NASA NTRS1985

A global geodetic reference frame from Lageos ranging (SL5.1AP)

A summary of the results obtained for a new comprehensive geodetic parameter solution from the analysis of Lageos laser ranging data for the period May 1976 to the end of 1982 is presented. Estimates of each component of the polar motion and earth rotation, the station coordinates, the value of the earth's gravitational constant GM, and the elements of the Lageos orbit comprise this SL5.1AP solution. The results differ from previously published values primarily through incorporation of more rigorous dynamic models for the ocean and solid earth tides. The precision of the geodetic parameters are on average 5-marc sec polar motion, 0.2-ms length of day, better than 5-cm center-of-mass geodetic positioning, 3-cm global baselines, and 2-cm regional baselines. An assessment of the contribution of systematic errors in the interstation distance determination is presented.

Smith, D. E.↗
NASA NTRS1985

On the geodetic applications of simultaneous range differences to Lageos

While the majority of the currently deployed satellite laser systems are of centimeter level precision, the accuracy of the geodetic products corresponds to the accuracy in which geodesists are interested. On several occasions, the best models are either not good enough or result in tedious computations which are required to achieve accuracies comparable to those of the observations. A possible alternative is related to the development of a new method of data analysis. This method involves the minimization of the effect of the systematic errors and, in particular, the minimization of errors arising from an incorrectly modeled orbit. The present paper provides a summary of the results of a study of this option, taking into account laser ranging data from Lageos.

Pavlis, E. C.↗
NASA NTRS1986

Geodesy by radio interferometry - Evidence for contemporary plate motion

Analysis of 211 very long baseline interferometry observing sessions carried out between November 1979 and August 1984 has yielded estimates of the distances between various radio telescopes located in North America and Europe. The average rate of change of the distances between four radio telescopes in North America (Haystack Observatory, Massachusetts; Westford Radio Telescope, Massachusetts; George R. Agassiz Station, Texas; and Owens Valley Radio Observatory, California) and one in Europe (Onsala Space Observatory, Sweden) obtained from the analysis of these data is 19 + or 10 mm/yr, where the (68 percent confidence interval) standard deviation is for the estimate of the rate of change of the Haystack-Onsala baseline length, the one determined most accurately from these data. This estimate of the standard deviation is dominated by the effects of correlated systematic errors due mostly to errors in the model used for the atmospheric delay which introduces errors in each baseline length estimate of 40 mm standard deviation and 60 days correlation time. (By contrast the statistical standard deviation is only 2 mm/yr). The estimated geologic rates of change of these baseline lengths, averaged over 10 to the 6th years, are 15 to 17 + or - 3 mm/yr for the various North American sites to Ondala.

Herring, T. A.↗
NASA NTRS1985

Global lower mesospheric water vapor revealed by LIMS observations

The Limb Infrared Monitor of the Stratospheric water vapor channel data analysis has been extended from the 1. mb level (about 48 km) to the .3 mb level (about 60 km) through a radiance averaging procedure and better understanding of systematic errors. The data show H2O mixing ratio peaks near the .5 mb level varying from 4 to 7 ppmv with latitude and season. Above this level the mixing ratio drops off quickly with altitude, but, due to experimental uncertainties, at an uncertain rate. The stratospheric results are virtually the same as determined from the archived LIMS results with a tropical hygropause and enhanced H2O concentration in the lower levels at high winter latitudes.

Gordley, L. L.↗
NASA NTRS1986

The radial velocity search for extrasolar planets

Stars are observed with a ground-based instrument designed to measure small changes in the line-of-sight velocities. The purpose of the observations is to detect large planets by the oscillatory reflex motion they induce on the stars they are orbiting. The instrument is an optical spectrometer for which wavelengths are first calibrated by transmission through a tunable Fabry-Perot etalon interferometer. Changes in the line-of-sight velocities are revealed by changes in the Doppler shift of the absorption-line spectra of stars. The scrambling of incident light by an optical fiber and the stability of wavelength calibration by a tilt-tunable Fabry-Perot etalon provide immunity to systematic errors that historically have effected more conventional radial velocity spectrographs. A cross-dispersed echelle spectrograph spatially separates the orders of constructive interference transmitted through the etalon. Selecting several echelle diffraction orders in the vicinity of 4250 to 4750 A, which are imaged on a CCD, about 350 points on the profile of the stellar spectrum are sampled by successive orders of interferometric transmission through the etalon.

Mcmillen, R. S.↗
NASA NTRS1986

Time dependent wind fields

Two tasks were performed: (1) determination of the accuracy of Seasat scatterometer, altimeter, and scanning multichannel microwave radiometer measurements of wind speed; and (2) application of Seasat altimeter measurements of sea level to study the spatial and temporal variability of geostrophic flow in the Antarctic Circumpolar Current. The results of the first task have identified systematic errors in wind speeds estimated by all three satellite sensors. However, in all cases the errors are correctable and corrected wind speeds agree between the three sensors to better than 1 ms sup -1 in 96-day 2 deg. latitude by 6 deg. longitude averages. The second task has resulted in development of a new technique for using altimeter sea level measurements to study the temporal variability of large scale sea level variations. Application of the technique to the Antarctic Circumpolar Current yielded new information about the ocean circulation in this region of the ocean that is poorly sampled by conventional ship-based measurements.

Chelton, D. B.↗