Download or read book Variability of the Lower Thermosphere Determined from Satellite Accelerometer Data written by Frank A. Marcos and published by . This book was released on 1978 with total page 52 pages. Available in PDF, EPUB and Kindle. Book excerpt: An extensive atmospheric density data base has been developed using accelerometer results from four low altitude satellites. The altitude range of the data is from 250 km down to as low as 140 km, with latitude coverage from 90 N to 90 S and local time periods that cover several 24-hr cycles. The data were obtained over a wide range of geomagnetic activity conditions. Solar radiation, as indicated by the 10.7-cm flux, was generally very low. Hence the data base applies mainly to solar minimum conditions. A description of the satellites, the accelerometer experiment, and the data base is given. Density variability is statistically analyzed in relation to selected atmospheric models. Particular attention is given to deviations from a normal distribution. Frequency distribitons of the data are described in terms of the mean value and the second, third, and fourth moments about the mean. This provides a more accurate description of extreme variations. The statistical properties of atmospheric variability are analyzed as a function of geomagnetic activity, latitude, altitude, and local time to develop a quantitative knowledge of unmodeled density variations. The results show that these accelerometer data will permit significant improvement in understanding the variations in the lower thermospheric density.
Download or read book Variability of the Lower Thermosphere Determined from Satellite Accelerometer Data written by Frank A. Marcos and published by . This book was released on 1978 with total page 46 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Lower thermosphere Neutral Density Profiles Derived from Satellite Accelerometer Data written by F. A. Marcos and published by . This book was released on 1976 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Cannon Ball II and SPADES satellites carried triaxial accelerometer systems for accurate measurement of neutral atmospheric density. Cannon Ball II was launched 6 August 1971 into a polar elliptic orbit in which the initial perigee was at the extremely low altitude of 132 km. SPADES was launched 11 July 1968 into a polar elliptic orbit in which the initial perigee was at 155 km. The data, analyzed to deduce an average density profile for each satellite for summer conditions in the northern hemisphere, are for the altitude region 135 to 250 km, where measurements have heretofore been extremely sparse. Comparisons were made with recent models and experimental data. These results are intended to be supplemented by those of lower-thermosphere studies now being carried out on accelerometer data from the Atmosphere Explorer satellites and a low-altitude Air Force satellite. Comprehensive analyses of accelerometer data low-altitude satellites will allow accurate modeling of the lower thermosphere. These models are required for improving calculation of the trajectories of Air Force systems vehicles and other spacecraft.
Download or read book A Global Thermospheric Density Model Based on Satellite Accelerometer Data written by Frank A. Marcos and published by . This book was released on 1982 with total page 48 pages. Available in PDF, EPUB and Kindle. Book excerpt: Measurements from the accelerometer experiments on four low-altitude satellites (S3-1 and Atmosphere Explorer-C, -D, and -E) have been combined to produce an empirical model of the neutral mass density from 140 to 240 km. Data from over a 8000 orbits are analyzed using the least-squares method of multiple linear regression. The resulting model gives density as a function of solar flux (for flux values 60 to 130 units), geomagnetic activity, day of year, local time, latitude and altitude. It provides a more accurate fit to the measured data than other available atmospheric models. Three commonly used models are evaluated by comparison of their predicted density variations with those of this empirical model.
Download or read book A Global Thermospheric Density Model Based on Satellite Accelerometer Data written by Frank A. Marcos and published by . This book was released on 1982 with total page 48 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Satellite Density Measurements with the Rotatable Calibration Accelerometer ROCA written by Frank A. Marcos and published by . This book was released on 1979 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt: Satellite accelerometer measurements of atmospheric density have provided significant improvement in our understanding of the structure and dynamics of the lower thermosphere. Derivation of accurate data with this technique requires removal of instrument bias from the total sensor output. The ROCA (Rotatable Calibration Accelerometer) experiment was flown to provide and orbital calibration capability on the three-axis stabilized S3-4 satellite. The ROCA sensitive axis could be operated in either of two orientations selectable by ground command. For density measurement (normal operating mode) the sensitive axis was aligned with the satellite velocity vector. For direct measurement of bias, the sensitive axis was aligned perpendicular to the velocity vector. Utilization of the inflight calibration technique showed a dependence of the bias upon the instrument operating temperature. Removal of the bias-temperature component from the total acceleration signal obtained in the normal operating mode permits derivation of accurate density data. Measurements of atmospheric density were obtained during approximately 600 orbits over a five month period. The resulting ROCA data will be utilized for improved satellite ephemeris computations and for detailed studies of the lower thermosphere, particularly those related to energy inputs at high latitudes. (Author).
Download or read book Lower Thermosphere Density Variations in the Southern Hemisphere written by F. A. Marcos and published by . This book was released on 1972 with total page 23 pages. Available in PDF, EPUB and Kindle. Book excerpt: Profiles of the neutral atmospheric density have been obtained at high and middle latitudes in the southern hemisphere from OV1-15 (SPACES) satellite accelerometer measurements. The data were obtained during a geomagnetically quiet period near the equinox, 24-28 September 1968, when the satellite was in a nearly down-dusk orbit. Perigee moved from 50 degrees S to 65 degrees S during this period. Measurements were made in the altitude range 170-250 km. Density values at dusk at high latitudes (before perigee) are less than those at midlatitudes (after perigee). The average difference between the high latitude and midlatitude data is 15 percent. A longitudinal variation is superimposed on the latitudinal gradients. Enhanced densities at high southern latitudes are found at longitudes near the south geomagnetic pole. (Author).
Download or read book Atmospheric Structure and Its Variations in the Lower Thermosphere written by K. S. W. Champion and published by . This book was released on 1963 with total page 36 pages. Available in PDF, EPUB and Kindle. Book excerpt: This is a report prepared for the intermediate altitude region (the lower thermosphere, lying between about 100 and 200 km). This region dif fers considerably from the lowest one, in which the volume of data makes statistical methods of analysis appropriate. For the highest region, a considerable amount of satellite data is available and the behavior of the atmosphere is reasonably well understood. Some rocket data is available for the lower thermosphere, but most of the meas uring instruments are experimental and a major part of the data analysis consists in studying the physics of the various corrections or calibra tion factors required. At the upper end of the altitude regime some satellite data is available. New density data includes the results from flights of two types of falling spheres, results from the diffusion of chemical clouds, and data from drag effects on three satellites with perigee altitudes near 200 km. The satellite data indicates a de pendence of density on the value of the magnetic A sub p index. Otherwise, the data shows more variation with the method of measurement and data reduction than actual variation of the atmosphere. (Author).
Download or read book Application of the Satellite Triaxial Accelerometer Experiment to Atmospheric Density and Wind Studies written by Frank A. Marcos and published by . This book was released on 1982 with total page 56 pages. Available in PDF, EPUB and Kindle. Book excerpt: A new satellite triaxial accelerometer system has been developed. This instrument has been flight-tested on three-axis stabilized satellites and has demonstrated the capability to accurately measure accelerations in the satellite's in-track, cross-track, and radial directions. The in-track data provide direct determination of atmospheric density. These data, obtained during a period of high solar flux, supplement the extensive set of measurements obtained by other accelerometer experiments during low solar flux conditions. The cross-track and radial results permit, for the first time, large-scale measurements of the zonal and, possibly, radial components of neutral atmospheric winds. These simultaneous wind and density data provide an extremely valuable input for the understanding of dynamic processes in the atmosphere and for the improvement of atmospheric models.
Download or read book Instrumentation Papers written by and published by . This book was released on 1978 with total page 304 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 500 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Hemispheric Asymmetries Detected from Satellite Ionization Gauge Measurements written by J. P. McIsaac and published by . This book was released on 1980 with total page 56 pages. Available in PDF, EPUB and Kindle. Book excerpt: esults obtained from the S3-1 ionization gauge measurements are statistically examined for hemispheric asymmetries in neutral density behavior. The parameter analyzed in this study is the mean value R, the ratio of the measured density to the Jacchia 71 model value. Over 150,000 values obtained during the period from November 1974 to May 1975 and covering the altitude range from perigee (about 160 km) to 300 km are considered. Results are presented in the form of frequency histograms and graphs of mean ratios vs latitude. Significant hemispherical asymmetries are found and described in detail.
Download or read book Dynamics and Structure of the Quiet Thermosphere written by K. S. W. Champion and published by . This book was released on 1974 with total page 36 pages. Available in PDF, EPUB and Kindle. Book excerpt: The COSPAR International Reference Atmospheres (CIRA) 1972 provides both a Mean International Reference Atmosphere of the thermosphere and a parametric set of models for the region. The models are based on knowledge of the thermosphere as of mid 1971. The differences in the diurnal variations of atmospheric density scale height obtained from satellite drag studies and temperatures obtained from incoherent radar scatter observations are probably due to different diurnal variations of density and temperature and not due to systematic discrepancies in the measurements. The answer to this question should be provided by data obtained from recently launched satellites ESRO IV, AEROS, and AE-C. The second major area of interest involves the absolute number densities and variations with time of day, latitude, and season of the major and minor constituents of the thermosphere. Recent data obtained with mass spectrometers and optical instruments are reviewed in addition to the results of theoretical composition calculations, which include turbulence and other transport effects.
Download or read book Report on Research at AFCRL written by Air Force Cambridge Research Laboratories (U.S.) and published by . This book was released on 1976 with total page 228 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book R D Abstracts written by Technology Reports Centre (Great Britain) and published by . This book was released on 1979 with total page 732 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Thermospheric Density and Wind Determination from Satellite Dynamics written by Eelco Doornbos and published by Springer Science & Business Media. This book was released on 2012-01-19 with total page 192 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Earth's atmosphere is often portrayed as a thin and finite blanket covering our planet, separate from the emptiness of outer space. In reality, the transition is gradual and a tiny fraction of the atmophere gases is still present at the altitude of low orbiting satellites. The very high velocities of these satellites ensure that their orbital motion can still be considerably affected by air density and wind. This influence can be measured using accelerometers and satellite tracking techniques. The opening chapters of this thesis provide an excellent introduction to the various disciplines that are involved in the interpretation of these observations: orbital mechanics, satellite aerodynamics and upper atmospheric physics. A subsequent chapter, at the heart of this work, covers advances in the algorithms used for processing satellite accelerometry and Two-Line Element (TLE) orbit data. The closing chapters provide an elaborate analysis of the resulting density and wind products, which are generating many opportunities for further research, to improve the modelling and understanding of the thermosphere system and its interactions with the lower atmosphere, the ionosphere-magnetosphere system and the Sun.
Download or read book Application of Satellite Accelerometer Data to Improve Density Models written by Frank A. Marcos and published by . This book was released on 1984 with total page 56 pages. Available in PDF, EPUB and Kindle. Book excerpt: Atmospheric density measurements obtained by the satellite accelerometer experiment provide data over a wide range of solar and geophysical conditions. These results are used in a preliminary evaluation of several atmospheric models. The model accuracies are compared by their mean values and standard deviations relative to the accelerometer data. Sources of model uncertainties and problems in reducing them are described. Long-term programs involving coordinated measurements, analyses of available data and theoretical studies are required along with development of more accurate indicators of solar and geomagnetic activity before models can show significant improvement. Keywords include: Satellite, Accelerometers, Atmospheric density measurements, Thermospheric model evaluations, Thermospheric density variability.
