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At least 577 records · Page 32
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NASA NTRS1981

Correlations between solar wind parameters and auroral kilometric radiation intensity

The relationship between solar wind properties and the influx of energy into the nightside auroral region as indicated by the intensity of auroral kilometric radiation is investigated. Smoothed Hawkeye satellite observations of auroral radiation at 178, 100 and 56.2 kHz for days 160 through 365 of 1974 are compared with solar wind data from the composite Solar Wind Plasma Data Set, most of which was supplied by the IMP-8 spacecraft. Correlations are made between smoothed daily averages of solar wind ion density, bulk flow speed, total IMF strength, electric field, solar wind speed in the southward direction, solar wind speed multiplied by total IMF strength, the substorm parameter epsilon and the Kp index. The greatest correlation is found between solar wind bulk flow speed and auroral radiation intensity, with a linear correlation coefficient of 0.78 for the 203 daily averages examined. A possible mechanism for the relationship may be related to the propagation into the nightside magnetosphere of low-frequency long-wavelength electrostatic waves produced in the magnetosheath by the solar wind.

Gallagher, D. L.↗
NASA NTRS1981

Global ozone long-term trends from satellite measurements and the response to solar activity variations

Analysis of global ozone variations for the period April 1970 to December 1975 was performed by using the reprocessed Nimbus 4 backscattered ultraviolet (BUV) measurements of total ozone. A correlation coefficient of 0.97 is found between the 6-month running mean of global mean total ozone (filtered for mean semiannual, annual, and quasibiennial variations) and the 10.7-cm solar activity index. Correcting ozone for a time-dependent latitudinal bias relative to Dobson ozone measurements reduces to 2-3% the global mean ozone variation over the solar cycle. The solar ultraviolet variability required in a one-dimensional time-dependent radiative photochemical model to account for the observed ozone variation appears to be consistent with recent solar UV observations.

Keating, G. M.↗
NASA NTRS1981

Global ozone - Solar activity relationship from satellite measurements

Global ozone variations are evaluated by analyzing satellite measurements, using the technique of integrating out dynamical effects causing large variations in total ozone at individual locations. Analysis of Nimbus 4 reprocessed BUV data was extended to cover the period from April 1970 through December 1975. Temporal and latitudinal variation of biases and yearly change in global biases between the satellite and ground based ozone measurements are indicated. The bias-corrected 6-month-running filtered global means are shown, and the correlation coefficient between ozone and the solar activity index remains high at 0.94. It is concluded that the results give a strong indication of an ozone-solar activity relationship that is caused by solar UV variability.

Keating, G. M.↗
NASA NTRS1982

Sensitivity analysis results of the effects of various parameters on composite design

Sensitivity analysis results are presented to assess the effects of a multitude of important parameters on fiber composite design and structural response. These results were obtained by using optimum design procedures in conjunction with sensitivity analyses. Sensitivity analyses were performed to assess the effects on composite optimum design and structural response of parameters such fiber transverse and shear properties, in situ matrix elastic and strength properties, correlation coefficients used in composite micromechanics and in combined strength predictions, processing variables, and perturbations of loading conditions. The results show that matrix properties, fiber volume ratio and small perturbations of the loading conditions have significant effects on certain composite structural responses. The remaining parameters have negligible effect.

Chamis, C. C.↗
NASA NTRS1982

Degree variances of the earth's potential, topography and its isostatic compensation

A spherical harmonic expansion of the earth's gravitational potential and equivalent rock topography to degree and order 180 is described. The potential implied by the topography considered as uncompensated and with isostatic compensation has been computed. Good agreement with the observed potential field is found when the depth of compensation in the Airy theory is assumed to be 50 km. At the higher degrees the correlation coefficient between the potential expansion and the equivalent rock topography is about 0.5. The Lachapelle equations for the topographic isostatic potential were tested using 1 x 1 deg equivalent rock topography. The degree variances agree at the lower degrees but at degree 36 the Lachapelle results using 5 deg data underestimate the potential degree variances by about one-third.

Rapp, R. H.↗
NASA NTRS1982

Space Shuttle Orbiter descent navigation

The entry operational sequence (OPS 3) begins approximately 2 hours prior to the deorbit maneuver and continues through atmospheric entry, terminal area energy management (TAEM), approach and landing, and rollout. During this flight phase, the navigation state vector is estimated by the Space Shuttle Orbiter onboard navigation system. This estimate is computed using a six-element sequential Kalman filter, which blends inertial measurement unit (IMU) delta-velocity data with external navaid data. The external navaids available to the filter are tactical air navigation (TACAN), barometric altimeter, and microwave scan beam landing system (MSBLS). Attention is given to the functional design of the Orbiter navigation system, the descent navigation sensors and measurement processing, predicted Kalman gains, correlation coefficients, and current flights navigation performance.

Montez, M. N.↗
NASA NTRS1984

Generating Random Number Pairs

Algorithm generates pairs drawn from bivariate normal distribution with any desired values of two means, two standard deviations, and correlation coefficient.

Campbell, C. W.↗
NASA NTRS1982

Analysis of high altitude remotely sensed data collected in the Nantucket Shoals experiment 4-15 May, 1981

High altitude ocean color scanner ratios of band 2 (456 to 476 nanometers) to band 4 (539 to 559 nanometers) and band 1 (418 to 438 nanometers) to band 3 (498 to 518 nanometers) had high correlation coefficient values (-0.928 and 0.891 respectively) with seven boat sampled chlorophyll a measurements. The range of chlorophyll a concentrations was small (1.7-2.58 mg/cu m.). Each ratio was used to calculate chlorophyll a values for the center pixel of each scan line on flight lines 5 and 6. The two ratios produced dissimilar chlorophyll a trends. Due to the high noise level in the scanner data, no reliable synoptic chlorophyll a map could be generated with either ratio algorithm.

Ohlhorst, C. W.↗
NASA NTRS1982

A comparison of HCMM surface temperatures with in situ temperature data

All HCMM required were processed. Calibrated and atmospherically corrected sea surface temperatures were developed for the Nantucket Shoals and Gulf of Mexico regions. These data were analyzed and the sea surface temperatures along the various transacts were compared with in situ data. The comparisons indicate that there is, on the average, a root mean square difference between the in situ data and the HCMM sea surface temperatures of + or - 1.0 C. The linear correlation coefficient was 0.97.

Vukovich, F. M.↗
NASA NTRS1982

Properties of AKR from an interferometer analysis of the ISEE-1 and -2 plasma wave data

Both ISEE 1 and 2 are equipped with identical wide-band analog plasma wave receivers which makes long baseline interferometry possible. A cross-correlation of the received signals from each spacecraft during periods of intense Auroral Kilometric Radiation (AKR) provides information on the source size of AKR. From the magnitude of the cross-correlation coefficient, measured over baselines from 40 Km to 8000 Km, an upper limit to the statistical source size can be determined. Thirty-five AKR events at 125 kHz are being analyzed. Preliminary results indicate that the apparent source sizes are smaller than .1 Re.

Baumback, M. M.↗
NASA NTRS1982

SEASAT SAR performance evaluation study

The performance of the SEASAT synthetic aperture radar (SAR) sensor was evaluated using data processed by the MDA digital processor. Two particular aspects are considered the location accuracy of image data, and the calibration of the measured backscatter amplitude of a set of corner reflectors. The image location accuracy was assessed by selecting identifiable targets in several scenes, converting their image location to UTM coordinates, and comparing the results to map sheets. The error standard deviation is measured to be approximately 30 meters. The amplitude was calibrated by measuring the responses of the Goldstone corner reflector array and comparing the results to theoretical values. A linear regression of the measured against theoretical values results in a slope of 0.954 with a correlation coefficient of 0.970.

Source record↗
NASA NTRS1982

Spectral scales in the atmospheric boundary layer

Wind data taken from 10 levels between 18 and 305 m were examined to determine the properties of atmospheric turbulence within and above the atmospheric surface layer into the PBL. The samples were averaged over 40 min intervals, with all periods of rain, fog, and other disturbances being eliminated from the 16 days of monitoring. Turbulence spectra were calculated using a fast Fourier transformation. The tower was located in rolling terrain covered with pine forests, waist-high scrub, and cultivated fields. Results are presented for the wavelength and Eulerian length scales, considering the neutral, stable, and unstable PBL. Correlation coefficients were found between velocity fluctuations and wavelengths for the stability classes. Good agreements were found for measured and computed spectra in all but unstable conditions.

Weber, A. H.↗
NASA NTRS1982

Dynamic modeling of vegetation change in arid lands

A general framework for a digital desertification monitoring system (DDMS) for assessing the worldwide desertification growth rate is presented. The system relies on the development of Landsat derived indicators to identify local processes signalling the growth of arid regions. A study area consisting of the eastern edge of the Niger River delta in Mali was used to characterize three indicators in terms of the covariance of the multispectral scanner (MSS) bands 2 and 4, the correlation of the two bands, and the percent variance expressed by the first eigenvalue. The scenes are imaged multitemporallly in a 400 x 400 pixel array to detect vegetation cover changes. Criteria were defined which characterized the decrease or increase of vegetation. It was determined that the correlation coefficients are the best indicators, and are easily computed.

Robinson, V. B.↗
NASA NTRS1983

Comparison of spherical double probe electric field measurements with plasma bulk flows in plasmas having densities less than 1 cm-3

For a three-hour period in the magnetotail over which plasma density varied from less than 0.1 to about 1/cu cm, comparisons of ISEE-1 spherical double probe (dawn to dusk) electric field measurements and ISEE-2 plasma flows (converted to electric fields) show the zero lag cross correlation coefficient between 768 second averages of the two data sets to have been 0.93. A statistical relative uncertainty between pairs of points in the two data sets, estimated by only including counting statistics in the plasma measurement and time variations of the observed electric field over the measurement interval, is able to account for at least 75 percent of the deviations between the two data sets. In agreement with simple Langmuir probe theory, it has been found that the spacecraft potential measured over the three-hour interval by the double probe instrument varied as the log of the product of the plasma density and the square root of the electron temperature.

Mozer, F. S.↗
NASA NTRS1983

Kinematics of velocity and vorticity correlations in turbulent flow

The kinematic problem of calculating second-order velocity moments from given values of the vorticity covariance is examined. Integral representation formulas for second-order velocity moments in terms of the two-point vorticity correlation tensor are derived. The special relationships existing between velocity moments in isotropic turbulence are expressed in terms of the integral formulas yielding several kinematic constraints on the two-point vorticity correlation tensor in isotropic turbulence. Numerical evaluation of these constraints suggests that a Gaussian curve may be the only form of the longitudinal velocity correlation coefficient which is consistent with the requirement of isotropy. It is shown that if this is the case, then a family of exact solutions to the decay of isotropic turbulence may be obtained which contains Batchelor's final period solution as a special case. In addition, the computed results suggest a method of approximating the integral representation formulas in general turbulent shear flows.

Bernard, P. S.↗
NASA NTRS1983

Comparison of winter-nocturnal geostationary satellite infrared-surface temperature with shelter-height temperature in Florida

Geostationary satellite surface temperatures derived from a Visible and Infrared Spin Scan Radiometer (VISSR) sensor (10.5 to 12.6 microns) were compared with 1.5-m air temperatures collected by a thermocouple on a traversing vehicle along rural highway transects in Florida, and with two fixed thermographs located in rural and agricultural areas. Statistical comparisons between satellite and 1.5-m observations yielded a mean correlation coefficient of 0.87 and an average sample standard deviation from regression of 1.57 C during clear nights for four winters (1978-1981). The satellite-temperature image of Lake Okeechobee was compared with its geographic outline for areal image registration. Manual overlays of temporal images were repeatable to within one pixel. Satellite-sensed water temperature of Lake Okeechobee was used as an indicator of satellite radiometer repeatability and stability.

Chen, E.↗
NASA NTRS1983

A correlation analysis of percent canopy closure versus TMS spectral response for selected forest sites in the San Juan National Forest, Colorado

The correlation of canopy closure with the signal response of individual thematic mapper simulator (TMS) bands for selected forest sites in the San Juan National Forest, Colorado was investigated. Ground truth consisted of a photointerpreted determination of percent canopy closure of 0 to 100 percent for 32 sites. The sites selected were situated on plateaus at an elevation of approximately 3 km with slope or = 10 percent. The predominant tree species were ponderosa pine and aspen. The mean TMS response per band per site was calculated from data acquired by aircraft during mid-September, 1981. A correlation analysis of TMS response vs. canopy closure resulted in the following correlation coefficients for bands 1 through 7, respectively: -0.757, -0.663, -0.666, -0.088, -0.797, -0.763. Two model regressions were applied to the TMS data set to create a map of predicted percent forest canopy closure for the study area. Results indicated percent predictive accuracies of 71, 74, and 57 for percent canopy closure classes of 0-25, 25-75, and 75-100, respectively.

Butera, M. K.↗
NASA NTRS1984

Regional correlation between TOMS total ozone from NIMBUS-7 satellite and geopotential height from the GLAS analysis

In order to study the relation between zone and the atmospheric circulation on a global scale the global correlation has been computed between TOMS total ozone measurements from NIMBUS-7 satellite and collocated geopotential heights analysis at all mandatory pressure levels between 1000-50 mb. The heights are obtained from the 4 deg x 5 deg GLAS analysis that uses both conventional (rawinsonde) and the operational TIROS-N satellite soundings but no ozone data. Zonal averages have been substracted to eliminate the correlation due merely to latitudinal dependence, and emphasize the correlation associated with synoptic features. Tables are presented with correlation coefficients for the four synoptic times covering the Pacific Ocean, Asia, Europe and the Atlantic Ocean, and United States regions. These coverages are approximate since NIMBUS-7 does not observe exactly the same region each day.

Munteanu, M. J.↗