A depolarization and attenuation experiment using the CTS satellite. Volume 2: Data
An experiment for measuring precipitation attenuation and depolarization on the CTS 11.7 GHz downlink is described.
Bostian, C. W.↗
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Development of far infrared attenuation to measure electron densities in cw pin discharge lasers
A two beam attenuation technique was devised to measure electron densities 10 to the 9th power to 10 to the 11th power cm/3 resolved to 1 cm, in a near atmospheric COFFEE laser discharge, using 496 micrometer and 1,220 micrometer radiations from CH3F, optically pumped by a CO2 laser. A far infrared generator was developed which was suitable except for a periodic intensity variation in FIR output deriving from frequency variation of the pump radiation.
Babcock, R. V.↗
Precipitation-attenuation studies based on measurements of ATS-6 20/30-GHz beacon signals at Clarksburg, Maryland
Radiometric sky temperature and minute precipitation measurements were intended to broaden the data base required to advance the understanding of the propagation characteristics of the earth-satellite path at frequencies over 10 GHz. Analyses of the data collected from the measurement program have established a detailed correlation between the satellite signal and the signals from auxiliary ground-based measurements. The indirectly derived statistics agreed reasonably well (or can be reconciled) with the earlier published results. The correlations may therefore be used for indirectly estimating long term cumulative attenuation statistics in the absence of direct satellite signal measurements.
Fang, D. J.↗
A depolarization and attenuation experiment using the CTS satellite
Rain attenuation and depolarization data collected on the communications technology satellite 11.7 GHz downlink, and changes made in equipment following rain leak damage to the parametric amplifier are discussed. A 15 GHz radar system is described.
Bostian, C. W.↗
Attenuation of upstream-generated low frequency noise by gas turbines
The acoustic transfer functions of low frequency (below 3500 Hz) noise through aircraft turbines were investigated. Model test results were compared with theoretical predictions in order to assess the validity of the theory. Component tests were conducted on both high pressure and low pressure model turbines. The influence of inlet temperature and turbine speed attenuation was evaluated, while the effects of turbine pressure ratio, blade-row choking, and additional downstream stages were determined. Preliminary identification of pertinent aeroacoustic correlating parameters was made.
Doyle, V. L.↗
Path attenuation statistics influenced by orientation of rain cells
The influence of path azimuth on fade and space diversity statistics associated with propagation along earth-satellite paths at a frequency of 18 GHz is examined. A radar rain reflectivity data base obtained during the summer of 1973 is injected into a modeling program and the attenuation along parallel earth-satellite paths are obtained for a conglomeration of azimuths. Statistics are separated into two groupings: one pertaining to earth-satellite paths oriented in the northwest-southeast and the other in the northeast-southwest quadrants using a fixed elevation angle of 45 deg. The latter case shows fading to be greater with a degraded space diversity suggesting rain cells to be elongated along this direction. Cell dimensions are analyzed for both sets of quadrants and are found to have average values larger by 2 km in the northeast-southwest quadrants; a result consistent with the fade and space diversity results. Examination of the wind direction for the 14 rain days of data analyzed shows good correlation of the average or median wind directions with the directions of maximum fading and degraded space diversity.
Goldhirsh, J.↗
Measured backscatter and attenuation properties, including polarization effects, of various dispersions at 0.9 micron
The optical properties of a wide variety of atmospheric dispersions were studied using a 0.9-micron lidar system which included a GaAs laser stack transmitter emitting a horizontally polarized beam of 4 milliradians vertical divergence and 1.5 milliradians horizontal divergence. A principal means for assessing optical properties was the polarization ratio, that is, the backscattered radiation power perpendicular to the transmitter beam divided by the backscattered radiation power parallel to the beam polarization. The ratio of the backscattered fraction to the attenuation coefficient was also determined. Data on the dispersion properties of black carbon smoke, road dust, fog, fair-weather cumulus clouds, snow and rain were obtained; the adverse effects of sunlight-induced background noise on the readings is also discussed.
Kohl, R. H.↗
Ground development and flight correlation of the vortex attenuating spline device
Data presented indicate that the wing-mounted spline is a effective vortex-attenuating device. A comparison of the vortex induced rolling moment results at a separation scale distance of 0.70 km with those measured in full scale flight indicate good agreement for the unattenuated vortex configuration. The comparison also indicates that the spline effectiveness in flight was greater than in the ground facility test. The results of an applications study show that, for the heavy commercial jet aircraft studied, use of the splines does result in some degradation of the climb gradient and rate of climb, but the aircraft should meet certification requirements.
Patterson, J. C., Jr.↗
Power law relationships for rain attenuation and reflectivity
The equivalent reflectivity, specific attenuation and volumetric backscatter cross section of rain are calculated and tabulated at a number of frequencies from 1 to 500 GHz using classical Mie theory. The first two parameters are shown to be closely approximated as functions of rain rate by the power law aR to the b power. The a's and b's are also tabulated and plotted for convenient reference.
Devasirvatham, D. M. J.↗
Numerical spatial marching techniques for estimating duct attenuation and source pressure profiles
A numerical method was developed that could predict the pressure distribution of a ducted source from far field pressure inputs. Using an initial value formulation, the two-dimensional homogeneous Helmholtz wave equation (no steady flow) was solved using explicit marching techniques. The Von Neumann method was used to develop relationships which describe how sound frequency and grid spacing effect numerical stability. At the present time, stability considerations limit the approach to high frequency sound. Sample calculations for both hard and soft wall ducts compare favorably to known boundary value solutions. In addition, assuming that reflections in the duct are small, this initial value approach was successfully used to determine the attenuation of a straight soft wall duct. Compared to conventional finite difference or finite element boundary value approaches, the numerical marching technique is orders of magnitude shorter in computation time and required computer storage and can be easily employed in problems involving high frequency sound.
Baumeister, K. J.↗
The effective aerosol attenuation on determination error of ocean and atmosphere temperatures by remote methods
This article contains a survey of literature on errors in establishing temperature of the underlying surface and the vertical profile of temperature in the 15 microns CO2 band when aerosol attenuation was not taken into account. Experimental data show the large contribution of the aerosol to total radiation attentuation. Evaluations are made of the relationship of the magnitude of establishment error to location and optical thickness of the aerosol layer.
Source record↗
CTS attenuation and cross-polarization measurements at 11.7 GHz
The results of data obtained 80 days preceding the solar eclipse shutdown of the CTS 11.7 GHz righthand circularly polarized beacon transmitter are presented. Attenuation and cross polarization isolation were measured. It was determined that depolarization presents a serious limitation to satellite system reliability when frequency reuse by polarization diversity is employed. A 27 db isolation margin would reduce reliability below 99.95%. For the same percentage the required fade margin was below 3 db.
Vogel, W. J.↗
Earth-satellite path attenuation statistics influenced by orientation of rain cells
It is examined whether there may be preferred azimuths for earth-satellite paths along which fading and space diversity statistics are influenced differently than along other azimuths. Such preferred directions may exist if individual rain cells are statistically elongated along them for the given climatological region. The analysis is performed using the rain reflectivity data base obtained at Wallops Island during June, July and August 1973 using a high resolution radar. It is found that in the vicinity of Wallops Island increased attenuation and poorer diversity gains exist along paths whose azimuths and base lines lie in the NE-SW quadrants as compared to the NW-SE sectors. This result suggests the dominance of the major axis of rain cells in these quadrants.
Goldhirsh, J.↗
Path- and area-integrated rainfall measurement by microwave attenuation in the 1-3 cm band
At a wavelength of about 0.9 cm, microwave attenuation is demonstrated to be linearly related to rainfall rate and independent of drop size distribution and temperature. In addition, practical methods for measuring path- and area-averaged rainfall rate are reviewed. A compromise between maximum path-averaged rainfall rate sensitivity and minimum sensing errors may be achieved by the use of one-way methods between the transmitter and the receiver, with a wavelength of 1.5 to 2.0 cm. Corrections for nonspherical drops and for multiple scattering are also discussed.
Atlas, D.↗
Numerical spatial marching techniques for estimating duct attenuation and source pressure profiles
A numerical method is developed that could predict the pressure distribution of a ducted source from far-field pressure inputs. Using an initial value formulation, the two-dimensional homogeneous Helmholtz wave equation (no steady flow) is solved using explicit marching techniques. The Von Neumann method is used to develop relationships which describe how sound frequency and grid spacing effect numerical stability. At the present time, stability considerations limit the approach to high frequency sound. Sample calculations for both hard and soft wall ducts compare favorably to known boundary value solutions. In addition, assuming that reflections in the duct are small, this initial value approach is successfully used to determine the attenuation of a straight soft wall duct. Compared to conventional finite difference or finite element boundary value approaches, the numerical marching technique is orders of magnitude shorter in computation time and required computer storage and can be easily employed in problems involving high frequency sound.
Baumeister, K. J.↗
Equations of state and impact-induced shock-wave attenuation on the moon
Equation of state formulations are considered in a framework that permits comparison with one-dimensional impedance match solutions. The problem considered is the peak pressures attained along the impact symmetry axis when a sphere impacts with a half-space. The regimes of melting and vaporization - in particular, incipiently melted, completely melted, incipiently vaporized, and completely vaporized states - are examined, and the pressures at which critical isentropes intersect the Hugoniots of iron and gabbroic anorthosite are considered. A means of representing the spatial attenuation of shock pressure along the impact axis by two regimes is introduced, and results for the near-field and far-field regime are presented. It is thought that the treatment can be used to obtain quantitative bounds on the impact velocity of the meteorite.
Ahrens, T. J.↗
Voltage-controlled attenuator with low phase shift
Five megahertz RF (radiofrequency) signal attenuator utilizing RF quadrature hybrid, and optically viable-resistance load controlled by lamp circuit exhibits little phase shift. Circuit is designed to help distribute standard RF signal of controlled amplitude, and phase throughout complex of facilities could be useful in application to precision test equipment and communication electronics.
Lutes, G. F., Jr.↗
CTS attenuation and cross polarization measurements at 11.7 GHz
The results of data obtained at The University of Texas at Austin during a total of 551 days of righthand circularly polarized transmission at 11.7 GHz from the CTS satellite are presented. Measured were attenuation, cross-polarization and rain rate. Results indicate that ice depolarization can be of significant importance.
Vogel, W. J.↗