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At least 307 records · Page 17

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NASA NTRS1985

Intercomparison of satellite ozone profile measurements

Ozone profile data are intercompared with those from the LIMS and SBUV flown on Nimbus 7, SAGE flown on Atmospheric Explorer Mission 2, and the Ultraviolet and Infrared Spectrometers flown on the SME. Ozone data were derived from the measurements with independently derived processing algorithms. The data cover different time periods and have different spatial and temporal resolutions. The similarities and differences between the individual data sets are determined with effort focused on directly comparing the spacecraft data sets in the form of individual profiles, zonal mean profiles and global analyses. Comparisons with ground data from balloons and Umkehr stations are made.

Fleig, A. J.↗

NASA NTRS1986

Intercomparison of numerical models of flaring coronal loops

The proposed Benchmark Problem consists of an infinitesimal magnetic flux tube containing a low-beta plasma. The field strength is assumed to be so large that the plasma can move only along the flux tube, whose shape remains invariant with time (i.e., the fluid motion is essentially one-dimensional). The flux tube cross section is taken to be constant over its entire length. In planar view the flux tube has a semi-circular shape, symmetric about its midpoint s = s sub max and intersecting the chromosphere-corona interface (CCI) perpendicularly at each foot point. The arc length from the loop apex to the CCI is 10,000 km. The flux tube extends an additional 2000 km below the CCI to include the chromosphere, which initially has a uniform temperature of 8000 K. The temperature at the top of the loop was fixed initially at 2 X 1 million K. The plasma is assumed to be a perfect gas (gamma = 5/3), consisting of pure hydrogen which is considered to be fully ionized at all temperatures. For simplicity, moreover, the electron and ion temperatures are taken to be everywhere equal at all times (corresponding to an artificially enhanced electron-ion collisional coupling). While there was more-or-less unanimous agreement as to certain global properties of the system behavior (peak temperature reached, thermal-wave time scales, etc.), no two groups could claim satisfactory accord when a more detailed comparison of solutions was attempted.

Kopp, R. A.↗

NASA NTRS1986

Intercomparison of independent estimates of cloud properties from simultaneous satellite observations

Preliminary results are reported from comparisons between two techniques for determining the cloud cover fraction within a satellite remote sensing scene. One method (PRM) quantifies cloud-free and cloud-filled areas on the bases of physical relationships between temperature, humidity, cloud optical properties and emitted radiation. The other approach (RSSM) derives the fractional cover from the spatial structure of radiances detected by the sensor. The HIRS (PRM) and the AVHRR (RSSM) instruments, tuned to IR wavelengths, on the TIROS-N polar-orbiting satellite furnished the trial data. Sample results are provided from scans at 15 and 11 microns over the Pacific Ocean.

Coakley, J. A., Jr.↗

NASA NTRS1986

Intercomparison between Nimbus-7 cirrus cloud data and ERB measurements

Nimbus-7 and Earth Radiation Budget (ERB) data were compared with the quantity of high, thin cirrus clouds over a 6 yr period. Three separate data analysis techniques are described which were used to derive cloud cover and total upwelling radiance values from the satellite data. Zonal average cirrus clouds amounts are compared with surface observations and SAGE satellite data, and comparisons are made between the cloud amount estimates made with ERB data and data from other Nimbus-7 instruments. All Nimbus-7 instrumental data indicated cloud amounts and frequency of occurrence patterns which were commensurate with surface observations, except in high latitude zones.

Yeh, H. Y. M.↗

NASA NTRS1986

Intercomparison of preliminary Earth Radiation Budget Satellite (ERBS) flux estimates and geostationary satellite multi-spectral 'VAS' radiance measurements

Results are reported from a preliminary study to evaluate the level of correlation and, if possible, establish relationships between the spectral radiances sensed by the GOES 6 satellite VISSR Atmospheric Sounder (VAS) and the ERBS longwave sensor. A data set for February 7, 1985 was selected which was scanned with both sensors flying over the region of the Gulf of Mexico. Techniques applied to enhance the equivalence of the data are delineated. Regression equations were applied to assess the levels of correlations for each subsatellite point compared.

Herman, L. D.↗

NASA NTRS1986

Results from the Balloon Ozone Intercomparison Campaign (BOIC)

Data from the BOIC which consisted of three balloon missions conducted in Palestine, Texas from June 1983 to March 1984 are presented. The BOIC was to assess the ability to perform ozone measurements from balloon platforms. The accuracy and precision of the various ozone measurement systems, which were composed of a photometer, a mass spectrometer, and solar UV absorption sensors, are evaluated. The ozone observations obtained with the instruments on the three flight missions are analyzed and intercompared. The flight in situ data are also compared to the National Bureau of Standards reference photometer, satellite measurements, and under simulated stratospheric pressure and ozone concentrations.

Hilsenrath, E.↗

NASA NTRS1986

The intercomparison of ozone measured from the SME and Nimbus-7 satellites on short and long time scales

The spatial and temporal characteristics of ozone density measured from the SBUV (Solar Backscatter Ultraviolet) spectrometer on Nimbus-7 and the UV and the UV and the IR spectrometers on SME (Solar Mesosphere Explorer) are compared in the altitude region near 50 km where the three data sets overlap. Their temporal characteristics, when averaged over the same longitude range, are remarkably similar with respect to seasonal variations and short term fluctuations induced by transient planetary waves. The long term trends in the three data sets, however, differ significantly with each other. Over the three year period after 1982 ozone mixing ratio at 1 mb decreased by about 10 percent based on SEUV measurements but increased by 12 and 30 percent respectively based on SME-IR and SME-UV measurements. None of these estimates are consistent with the predicted decrease of about 2 percent based on solar UV flux and temperature changes during this period.

Chandra, S.↗

NASA NTRS1987

An intercomparison of nitrogen-containing species in Nimbus 7 LIMS and SAMS data

Odd-nitrogen chemistry and transport are analyzed using a two-dimensional model and Nimbus 7 data. The Nimbus 7 data include: measurements of O3, NO2, HNO3, H2O, and temperature by the LIMS instrument; N2O, CH4, and temperature measurements by the SAMS instrument; and O3 data from the SBUV instrument. The characteristics of the two-dimensional model used in the study, a modified Guthrie et al. (1984) model, are described. NO2 and HNO3 are calculated using the two-dimensional model, and the computed data are compared with the LIMS NO2 and HNO3 measurements. The model uncertainties are computed based on the photochemical equilibrium assumption, and the role of stratospheric dynamics in determining NO2 and HNO3 is discussed. It is observed that there is good correlation between the LIMS and model data in the upper stratosphere; however, the data do not correspond in the lower stratosphere. The effect of nitrogen sources, such as lightning, on the stratospheric odd nitrogen distribution is examined.

Jackman, Charles H.↗

NASA NTRS1986

An analysis and intercomparison of VLBI nutation estimates

Nutation estimates from long duration VLBI experiments conducted by the Deep Space Network and reduced at JPL were compared with similar estimates from the IRIS/Polaris data reduced at Harvard. The two series were found to have an rms difference of 1.6 milliarcsec or less, and both exhibited the existence of seasonal errors in the IAU 1980 nutation theory. Most of the observed seasonal discrepancies could be removed by changing the period of the free core resonance to 431.5 solar days. The VLBI data constrain the resonance damping time to be at least one decade, and possibly much longer. Any free core nutation has an amplitude of less than 1 milliarcsec. Crude estimates of the atmospheric forcing of this resonance indicate that meteorological forcing could easily explain the observed free core nutation.

Eubanks, T. M.↗

NASA NTRS1986

Intercomparison of polar motion measurements during the MERIT period

Polar motion estimates obtained by satellite laser ranging (SLR) and VLBI are analyzed and compared. The JPL Kalman filter was utilized to smooth the polar motion estimates. Variations in the smoothing residuals for the X and Y components of polar motion for SLR and VLBI are examined. It is observed that the rms differences between the SLR and VLBI estimates for X and Y are about 2-3 marcsec. Power spectra of the differences are studied in order to measure possible periodic systematic errors. The data reveal that the SLR and VLBI polar motion data have a rms difference of about 15-20 marcsec and no significant systematic errors.

Steppe, J. A.↗

NASA NTRS1987

An intercomparison technique for measuring thermal attachment cross sections and rate constants in distinct final channels

A new technique is introduced for comparing negative-ion signal rates in which a common ion is produced by dissociative attachment in a series of molecules. Measurements are carried out at electron energies less than 100 MeV and at resolutions of 6-8 MeV (FWHM). The technique is demonstrated by detection of the Cl(-) signal in CFCl3, CCl4, CF2Cl2, 1,1,2-C2Cl3F3, 1,1,1-C2Cl3F3 and C2Cl4. Measurements for 1,1,1-C2Cl3F3 show that there is a significant open channel, other than Cl(-) formation, which accounts for about 60 percent of negative-ion formation in thermal-multiple-collision (swarm) experiments. Channel cross sections and rate constants are given for the process Cl(-)/1,1,1-Cl2Cl3F3, as well as in C2Cl4, for the separate channels Cl(-)/C2Cl4 and C2Cl4(-)/C2Cl4.

Alajajian, S. H.↗

NASA NTRS1987

Intercomparison among plasma wake models for plasmaspheric and ionospheric conditions

The angular distributions of ions in the wake of a body moving through a space plasma computed from three different models are compared in order to investigate wake current depletion ratios under conditions simulating the topside ionosphere and plasmasphere. Results demonstrate the importance of taking into account the thermal flux at low Mach numbers and the angular acceptance of ion detectors in making theory-experiment comparisons. For all models considered, gradients in the angular variations of the fluxes are shown to be steeper near the wake-ambient interface than closer to the maximum rarefaction region.

Samir, U.↗

NASA NTRS1988

Intercomparison of satellite-derived cloud analyses for the Arctic Ocean in spring and summer

Several methods of deriving Arctic cloud information, primarily from satellite imagery, have been intercompared. The comparisons help in establishing what cloud information is most readily determined in polar regions from satellite data analysis. The analyses for spring-summer conditions show broad agreement, but subjective errors affecting some geographical areas and cloud types are apparent. The results suggest that visible and thermal infrared data may be insufficient for adequate cloud mapping over some Arctic surfaces.

Mcguffie, K.↗

NASA NTRS1988

Intercomparison of solar total irradiance data from recent spacecraft measurements

Earth Radiation Budget Experiment solar total irradiance data obtained by the solar monitors of the NOAA 9 and 10 spacecraft are presently compared with those obtained by the Solar Maximum Mission's Active Cavity Irradiance Monitor 1, as well as sounding rockets and the Nimbus 7 Earth Radiation Budget channel 10C. A disparity is noted among total irradiance values obtained in near-simultaneous measurements with absolute pyrheliometers of similar design and operational modes which (1) indicates the uncertainty associated with currently available instruments, and (2) recommends intercalibration of electrically self-calibrating pyrheliometers from spacecraft.

Mecherikunnel, A. T.↗

NASA NTRS1988

Intercomparison of synthetic- and real-aperture radar observations of Arctic sea ice during winter MIZEX '87

Active microwave measurements were made of various sea ice forms in March and April 1987 during the Marginal Ice Zone Experiment, at 1, 5, 10, 18, and 35 GHz using a synthetic aperture radar (SAR) and helicopter and ship-based scatterometers. The X-band (9.8 GHz) SAR data were compared to the scatterometer data and it was determined that for 5 GHz and higher frequencies both the SAR and scatterometers can differentiate open water, new ice (5 to 30 cm), first-year ice with rubble (0.60 -1.5 m), and multiyear ice. The analysis further confirmed that the C-band (5 GHz) SAR's flying on ESA ERS-1 and Radarsat will differentiate the mentioned ice types.

Schuchmann, R. A.↗

NASA NTRS1988

Intercomparison of satellite laser ranging accuracy of three NASA stations through collocation

The accuracy of laser ranging has been evaluated through comparisons of simultaneous LAGEOS satellite-borne laser ranging data received at three NASA tracking stations in support of the Crustal Dynamics project. Single-shot satellite ranging precisions of 8, 14, and 30 mm have been demonstrated at the three ground stations, with a stability better than 3 mm. The data-processing software used were POLYQUICK and GEODYN; a consistent degree of agreement between the three stations of less than 1 cm is obtained.

Varghese, T.↗

NASA NTRS1988

An intercomparison of results from ferrous sulphate and photolytic converter techniques for measurements of NO(x) made during the NASA GTE/CITE 1 aircraft program

Two techniques designed for measurements of NO(x (NO + NO2) were intercompared during aircraft flights made in the spring of 1984 in the middle free troposphere over the eastern Pacific Ocean and southwestern U.S. One NO chemiluminescence instrument was equipped with a ferrous sulphate converter, another with a photolytic converter. The ferrous sulphate-equipped instrument was apparently much less specific for NO2. It registered levels about three times larger than the photolytic converter and gave NO2/NO ratios that were much larger than photochemical calculations would indicate as reasonable. Additionally, the results imply that active NO(x) was only 10-20 percent of the total odd nitrogen in the middle free troposphere.

Ridley, B. A.↗

NASA NTRS1988

Intercomparison of NO column measurements during MAP/GLOBUS 1985

Simultaneous NO column measurements made in France in September, 1985, using several techniques, are compared with one another. The observed NO distributions vary significantly from day to day. It is shown that NO measurements using IR or UV absorption are self-consistent and show good agreement with predictions from a one-dimensional photochemical model. In situ chemiluminescent measurements produced NO columns which were systematically higher than those predicted.

Mckenzie, R. L.↗