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At least 163 records · Page 9

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NASA NTRS1980

Measurement of Aircraft Speed and Altitude

Problems involved in measuring speed and altitude with pressure-actuated instruments (altimeter, airspeed indicator, true-airspeed indicator, Machmeter, and vertical-speed indicator) are examined. Equations relating total pressure and static pressure to the five flight quantities are presented, and criteria for the design of total and static pressure tubes are given. Calibrations of typical static pressure installations (fuselage nose, wing tip, vertical fin, and fuselage vent) are presented, various methods for flight calibration of these installations are described, and the calibration of a particular installation by two of the methods is described in detail. Equations are given for estimating the effects of pressure lag and leaks. Test procedures for the laboratory calibration of the five instruments are described, and accuracies of mechanical and electrical instruments are presented. Operational use of the altimeter for terrain clearance and vertical separation of aircraft is discussed, along with flight technical errors and overall altitude errors of aircraft in cruise operations. Altitude-measuring techniques based on a variety of properties of the Earth and the atmosphere are included. Two appendixes present airspeed and altitude tables and sample calculations for determining the various flight parameters from measured total and static pressures.

Gracey, W.↗

NASA NTRS1980

Observations of neutral wind profiles between 115- and 175-km altitude in the dayside auroral oval

Lithium trail neutral wind measurements have been made in the morning dayside auroral oval as a function of altitude. During all four experiments the winds displayed a large altitude shear. In the most extreme case the wind at 135-km altitude was toward the south at 210 m/s, and at 185-km altitude toward the northwest at 170 m/s. A one-dimensional numerical solution to the Navier Stokes equation including an initial steady-state wind profile, viscosity, pressure gradient, Lorenz force and the Coriolis force was made in order to study the effect of auroral processes on the neutral atmosphere. Since electric fields and plasma density were measured, the Lorenz force could be modeled with reasonable accuracy. The pressure gradient was determined in an iterative way as a best fit to the observations. Within the limitations of a one-dimensional model the numerical solution is in reasonable agreement with one of the observations, which is applicable to such a modeling, and indicates that both Lorenz forces and pressure gradients due to auroral processes are required to explain the observation.

Pereira, E.↗

NASA NTRS1981

The altitude distribution of the Venus ultraviolet nightglow and implications on vertical transport

The altitude distribution of the nitric oxide nightglow was measured with an ultraviolet spectrometer on board Pioneer Venus, in order to study the effects of the distribution on the Venus nightside lower thermosphere transport properties. Limb profiles were obtained with an 8 ms integration period on several orbits near periapsis. The observations were made between P minus 2 min and P plus 4 min, where altitude ranges between 150 and 350 km, and latitude varies from 24 degrees N to 9 degrees S. A method independent of the spacecraft attitude data was used to fit the observed limb profiles, and to find the altitude of the maximum of the layer (115 plus or minus 2 km), and the topside scale height (about 3 km). It is shown that downward transport by diffusion alone is not sufficient, and if vertical motion is parameterized by eddy diffusion, an eddy diffusion coefficient is deduced from the altitude of the layer.

Gerard, J. C.↗

NASA NTRS1982

Plasma and electric field boundaries at high and low altitudes on July 29, 1977

Hot plasma observations at high and low altitudes were compared. The plasma ion composition at high altitudes outside the plasmasphere was 0+. Heavy ions were also observed at low altitudes outside the plasmasphere. It is shown that at times these ions are found well below the plasmapause inside the plasmasphere. Comparisons of the low altitude plasma and dc electric fields show that the outer limits of the plasmasphere is not always corotating at the low L-shells. The corotation boundary, the estimated plasmapause boundary at the boundary of the inner edge of plasma sheet ions were at the same position. The inner edge of plasma sheet electrons is observed at higher latitudes than the plasmasphere boundary during disturbed times. The inner edge of the plasma sheaths shows a strong dawn to dusk asymmetry. At the same time the inner edge of the ring current and plasma sheath also moves to high latitudes reflecting an apparent inflation of the magnetosphere.

Fennell, J. F.↗

NASA NTRS1981

Remote detection of the maximum altitude of equatorial ionospheric plasma bubbles

Nearly 200 post-sunset low-altitude passes of the Alouette 2 and ISIS 1 satellites near the dip equator are studied in order to find the maximum ionospheric plasma bubble altitudes, which are determined by calculating the apex altitude of the magnetic field line passing through the satellite when it is immersed in a bubble. The calculations are made only upon the observation of conjugate hemisphere ionospheric echoes, which result from ducted HF sounder signals that are guided along field-aligned irregularities within the plasma depletion. The maximum bubble altitudes corresponding to the three longitude sectors centered on zero deg, 75 deg W, and 105 deg E, are found to often exceed 1000 km, but seldom 3000 km. The electron density depletions within these field-aligned bubbles, as measured at the point of satellite encounter with the topside ionosphere, are generally less than a factor of two but may exceed a factor of ten.

Benson, R. F.↗

NASA NTRS1983

Comparison of low-altitude wind-shear statistics derived from measured and proposed standard wind profiles

Wind shear statistics were calculated for a simulated set of wind profiles based on a proposed standard wind field data base. Wind shears were grouped in altitude in altitude bands of 100 ft between 100 and 1400 ft and in wind shear increments of 0.025 knot/ft. Frequency distributions, means, and standard deviations for each altitude band were derived for the total sample were derived for both sets. It was found that frequency distributions in each altitude band for the simulated data set were more dispersed below 800 ft and less dispersed above 900 ft than those for the measured data set. Total sample frequency of occurrence for the two data sets was about equal for wind shear values between +0.075 knot/ft, but the simulated data set had significantly larger values for all wind shears outside these boundaries. It is shown that normal distribution in both data sets neither data set was normally distributed; similar results are observed from the cumulative frequency distributions.

Usry, J. W.↗

NASA NTRS1984

System for indicating fuel-efficient aircraft altitude

A method and apparatus are provided for indicating the altitude at which an aircraft should fly so the W/d ratio (weight of the aircraft divided by the density of air) more closely approaches the optimum W/d for the aircraft. A passive microwave radiometer on the aircraft is directed at different angles with respect to the horizon to determine the air temperature, and therefore the density of the air, at different altitudes. The weight of the aircraft is known. The altitude of the aircraft is changed to fly the aircraft at an altitude at which is W/d ratio more closely approaches the optimum W/d ratio for that aircraft.

Gary, B. L.↗

NASA NTRS1984

Low altitude wind shear statistics derived from measured and FAA proposed standard wind profiles

Wind shear statistics were calculated for a simulated data set using wind profiles proposed as a standard and compared to statistics derived from measured wind profile data. Wind shear values were grouped in altitude bands of 100 ft between 100 and 1400 ft, and in wind shear increments of 0.025 kt/ft between + or - 0.600 kt/ft for the simulated data set and between + or - 0.200 kt/ft for the measured set. No values existed outside the + or - 0.200 kt/ft boundaries for the measured data. Frequency distributions, means, and standard deviations were derived for each altitude band for both data sets, and compared. Also, frequency distributions were derived for the total sample for both data sets and compared. Frequency of occurrence of a given wind shear was about the same for both data sets for wind shears, but less than + or 0.10 kt/ft, but the simulated data set had larger values outside these boundaries. Neglecting the vertical wind component did not significantly affect the statistics for these data sets. The frequency of occurrence of wind shears for the flight measured data was essentially the same for each altitude band and the total sample, but the simulated data distributions were different for each altitude band. The larger wind shears for the flight measured data were found to have short durations.

Dunham, R. E., Jr.↗

NASA NTRS1984

Comparison of tropopause altitude determination by the Platteville Radar, Sunset Radar and the NWS Rawinsonde

During the month of March, 1981 the Sunset and Platteville Radar and Platteville Radar were operated primarily with vertical antenna beams. These radars are both VHF ST (Stratosphere-Troposphere) radars. The separation between them was 63 km, the Sunset site located in the foothills of the Rocky Mountains and the Platteville site was in the plains, just east of the mountains. Both radars were operated continuously for about three weeks with a time resolution of a few minutes. Both made measurements in the 4 to 20 km altitude interval with an altitude sampling of 1.2 km. The purpose is to compare the estimation of the altitude of the tropopause by these two radars with the altitude of the tropopause derived from standard NWS rawinsondes.

Green, J. L.↗

NASA NTRS1985

Variability of cloudiness at airline cruise altitudes from GASP measurements

Additional statistics relating to the climatology of cloud cover at airline cruise altitudes are presented. The data were obtained between 1975 and 1979 from commercial airliners participating in the Global Atmospheric Sampling Program (GASP). The statistics describe the seasonal, latitudinal and altitudinal variation in cloudiness parameters as well as differences in the high-altitude cloud structure attributed to cyclone and convective-cloud generation processes. The latitudinal distribution of cloud cover derived form the GASP data was found to agree with high-altitude satellite observations. The relationships between three different measures of cloudiness and the relative vorticity at high altitudes is also discussed.

Jasperson, W. H.↗

NASA NTRS1985

Dependence of Venus ionopause altitude and ionospheric magnetic field on solar wind dynamic pressure

The shape of the dayside Venus ionopause, and its dependence on solar wind parameters, is examined using Pioneer Venus Orbiter field and particle data. The ionopause is defined here as the altitude of pressure equality between magnetosheath pressure and ionospheric thermal pressure; its typical altitudes range from about 300 km near the subsolar point to about 900 km near the terminator. A strong correlation between ionopause altitude and magnetosheath magnetic pressure is demonstrated; correlation between magnetic pressure and the normally incident component of solar wind dynamic pressure is also evident. The data support the hypothesis of control of the ionopause altitude by solar wind dynamic pressure, manifested in the sheath as magnetic pressure. The presence of large scale magnetic fields in the ionosphere is observed primarily when dynamic pressure is high and the ionopause is low.

Phillips, J. L.↗

NASA NTRS1986

The relationship of intravascular bubbles to bends at altitude

In response to recent findings attesting to a correlation between intravehicular bubbling and decompression sickness at intermediate altitudes, an attempt was made to define a minimum pressure for a pressure suit which would obviate the need for prebreathing 100 percent oxygen prior to extravehicular activity (EVA). Fifty-seven male subjects were exposed to altitudes ranging from 16,000 to 30,000 ft in two separate protocols. The first was designed to determine a pressure at which no bends occurred if a crewmember were decompressed from a sea level space station pressure just prior to EVA without prebreathing 100 percent oxygen. The other study was designed to define an altitude and exercise regimen at which bends-susceptible and bends-resistant crewmembers could be separated. It is shown that the close association which exists between severe bubbling and bends at a pressure altitude of 4.3 psia (30,000 ft) decreases as pressure is increased and essentially disappears at pressures less than or equal to 7.8 psia (16,000 ft).

Krutz, R. W.↗

NASA NTRS1989

High-Altitude Turbulence For Supersonic Airplanes

Report reviews accumulated knowledge of atmospheric turbulence at high altitudes. Discusses characteristics of high-altitude turbulence and associated meteorological features, with emphasis on data obtained by flight research conducted in XB-70 and YF-12A prototype aircraft. Gives example of numerical simulation of gravity waves to illustrate potential contribution of such studies to understanding of atmospheric turbulence. Products of such efforts include ability to extend estimates of transient properties of atmospheric altitudes below 20 km to altitudes as high as 80 km for use in design and flight simulation of future advanced aerospace vehicles. Enables more accurate assessment of feasibility of remote sensors and computer systems aboard airplanes to process measurements into advanced warnings of turbulence.

Ehernberger, L. J.↗

NASA NTRS1988

Quantitative observations of the behavior of anomalous low altitude ClO in the Antarctic spring Stratosphere, 1987

During the second National Ozone Expedition ground-based observations at McMurdo Station Antarctica were performed which resulted in a second season's measurement of abnormally large amounts of ClO in the Antarctic spring stratosphere. The original measurements of 1986, in which the presence of this anomalous layer was first discovered, were limited in low altitude recovery of the ClO mixing ratio profile by the restrictions of the spectral bandwidth (256 MHz) which was used to measure the pressure-broadened ClO emission line shape. The 1987 measurements were marked by the use of twice the spectral bandpass employed the previous year, and allow a better characterization of the ClO mixing ratio profile in the critical altitude range 18 to 25 km. In-situ aircraft measurements of ClO made over the Palmer Peninsula during Aug. and Sept. of 1987 by Anderson, et al. effectively determined the important question of the ClO mixing ratio profile at altitudes inaccessible to our technique, below approximately 18 to 18.5 km. These flights did not penetrate further than 75 deg S, however, (vs 78 deg S for McMurdo) and were thus limited to coverage near the outer boundaries of the region of severest ozone depletion over Antarctica in 1987, did not reach an altitude convincingly above that of the peak mixing ratio for ClO, and were not able to make significant observations of the diurnal variation of ClO. The two techniques, and the body of data recovered by each, thus complement one another in producing a full picture of the anomalous ClO layer intimately connected with the region of Antarctic spring ozone depletion. An analysis is presented of the mixing ratio profile from approximately 18 to 45 km, the diurnal behavior, and the secular change in ClO over McMurdo Station during Sept. and early Oct. 1987.

Dezafra, R. L.↗

NASA NTRS1990

Collision probability at low altitudes resulting from elliptical orbits

The probability of collision between a spacecraft and another object is calculated for various altitude and orbit conditions, and factors affecting the probability are discussed. It is shown that a collision can only occur when the spacecraft is located at an altitude which is between the perigee and apogee altitudes of the object and that the probability per unit time is largest when the orbit of the object is nearly circular. However, at low altitudes, the atmospheric drag causes changes with time of the perigee and the apogee, such that circular orbits have a much shorter lifetime than many of the elliptical orbits. Thus, when the collision probability is integrated over the lifetime of the orbiting object, some elliptical orbits are found to have much higher total collision probability than circular orbits. Rocket bodies used to boost payloads from low earth orbit to geosynchronous orbit are an example of objects in these elliptical orbits.

Kessler, Donald J.↗

NASA NTRS1992

High altitude solar power platform

Solar power is a preeminent alternative to conventional aircraft propulsion. With the continued advances in solar cells, fuel cells, and composite materials technology, the solar powered airplane is no longer a simple curiosity constrained to flights of several feet in altitude or minutes of duration. A high altitude solar powered platform (HASPP) has several potential missions, including communications and agriculture. In remote areas, a HASPP could be used as a communication link. In large farming areas, a HASPP could perform remote sensing of crops. The impact of HASPP in continuous flight for one year on agricultural monitoring mission is presented. This mission provides farmers with near real-time data twice daily from an altitude which allows excellant resolution on water conditions, crop diseases, and insect infestation. Accurate, timely data will enable farmers to increase their yield and efficiency. A design for HASPP for the foregoing mission is presented. In the design power derived from solar cells covering the wings is used for propulsion, avionics, and sensors. Excess power produced midday will be stored in fuel cells for use at night to maintain altitude and course.

Bailey, M. D.↗

NASA NTRS1990

Differences in the day and night longwave fluxes at satellite altitude for sun-synchronous NOAA-9 nonscanning sensors

The outgoing LW flux determined by using the data measured by four nonscanning sensors at satellite altitude is reported. The outgoing LW fluxes for MFOV and WFOV sensors at satellite altitude are determined by subtracting the SW fluxes from the total sensors. Results for 1985 and 1986 are discussed. The nighttime LW flux determined by using the MFOV-T channel at the satellite altitude is found to be constant from month to month within 1 W/sq m, while the LW flux from WFOV-T channel varies within 2 to 3 W sq m. The high value for the WFOV-T channel is attributed to the effects of sun-blips on the measurements involved. The main advantage of using day/night longwave flux differences at satellite altitude is that the consistencies of nonscanner sensors can be checked very quickly.

Pandey, Dhirendra K.↗

NASA NTRS1991

Observations from a constant-altitude stratospheric balloon

The paper describes a constant-altitude stratospheric balloon system, called Earthwinds, designed for high-altitude atmospheric observations. Special attention is given to the balloon's variable ballast system for altitude control; reactions of the balloon system to air motions in a stratified atmosphere; instruments for locating the balloon position, controlling the altitude, and making observations of atmospheric movements; balloon dynamics; and the atmospheric phenomena that will be observed by the balloon instruments.

Mollo-Christensen, Erik↗