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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1971

Further studies of propellant sloshing under low-gravity conditions

A variational integral is formulated from Hamilton's Principle and is proved to be equivalent to the usual differential equations of low-gravity sloshing in ellipsoidal tanks. It is shown that for a zero-degree contact angle the contact line boundary condition corresponds to the stuck condition, a result that is due to the linearization of the equations and the ambiguity in the definition of the wave height at the wall. The variational integral is solved by a Rayleigh-Ritz technique. Results for slosh frequency when the free surface is not bent-over compare well with previous numerical solutions. When the free surface is bent over, however, the results for slosh frequency are considerably larger than those predicted by previous finite-difference, numerical approaches: the difference may be caused by the use of a zero degree contact angle in the present theory in contrast to the nonzero contact angle used in the numerical approaches.

Dodge, F. T.↗
NASA NTRS1974

Engineering studies related to the GEOS-C radar altimeter

Experiment requirements, technical characteristics, and GEOS-C radar altimeter related analyses are discussed along with results of a study on engineering test data requirements. Statistical analyses related to determination of wave height resolution achievable as a function of system characteristics and averaging period are described, in addition to a discussion on the desirability of using computer procedures to compensate for altitude tracker time-jitter. Data processing considerations for the GEOS-C system are examined. An extensive analysis of the spatial filter effect is given and results of a computation of geoidal power spectral density, based on Skylab altimeter data, is displayed and interpreted in terms of projected GEOS-C random errors. This information is then used in deriving minimum-mean-square filter procedures for both geoid undulation and slope data. The characteristics of mean received waveforms as a function of off-nadir angle are used to obtain tracker bias as a function of sea state and pointing angle. The angle estimation process proposed by the GEOS-C hardware contractor is also investigated from a standpoint of achievable angular resolution.

Miller, L. S.↗
NASA NTRS1974

Computer extension and analytic continuation of Stokes' expansion for gravity waves

Stokes' infinitesimal-wave expansion for steady progressive free-surface waves has been extended to high order using a computer to perform the coefficient arithmetic. Stokes' expansion has been found to be incapable of yielding the highest wave for any value of the water depth since convergence is limited by a square-root branch-point some distance short of the maximum. By reformulating the problem using a different independent parameter, the highest waves are obtained correctly. Series summation and analytic continuation are facilitated by the use of Pade approximants. The method is valid in principle for any finite value of the wavelength and solutions of high accuracy can be obtained for most values of the wave height and water depth.

Schwartz, L. W.↗
NASA NTRS1975

Bistatic radar sea state monitoring system design

Remote measurement of the two-dimensional surface wave height spectrum of the ocean by the use of bistatic radar techniques was examined. Potential feasibility and experimental verification by field experiment are suggested. The required experimental hardware is defined along with the designing, assembling, and testing of several required experimental hardware components.

Ruck, G. T.↗
NASA NTRS1975

Bistatic radar sea state monitoring field test

Recent advances in understanding the physical phenomena controlling the interaction of electromagnetic energy with the ocean surface have revealed the possiblity of remote measurement of the two-dimensional surface wave height spectrum of the ocean using bistatic radar techniques. The basic feasibility of such a technique operating at frequencies in the HF region (3 to 30 MHz) was examined during previous studies and hardware for an experimental verification experiment was specified. The activities have resulted in a determination of the required hardware and system parameters for both satellite and aircraft systems, the development, assembly, and testing of hardware for an experimental aircraft system, the development and initial testing of data processing procedures, and the conduct of an initial flight test experiment. Activities were devoted to completing the assembly and testing of the experimental hardware, completing the experiment planning, conducting a field test experiment, and the processing and analysis of the experimental data. Even though directional spectrum maps of the test area cannot be generated from the measured data, the hardware concept employed appears viable, and solutions to the problems encountered have been identified.

Ruck, G. T.↗
NASA NTRS1974

SEASAT-A - A user oriented systems design

The SEASAT-A spacecraft is tentatively scheduled for launch in 1978 into a nearly circular orbit with an altitude of approximately 800 km. The spacecraft is to demonstrate a capability for the global monitoring of wave height and spectra, surface winds, ocean temperature, and current patterns. Other objectives include the charting of ice fields and a mapping of the global geoid. The sensors to be carried by the spacecraft are discussed and a description is given of the satellite system and the subsystems.

Mccandless, S. W., Jr.↗
NASA NTRS1974

Bistatic sea state radar monitoring system and applications to marine geodesy

The bistatic scattering of high frequency radio waves can be used to observe directional ocean-wave spectra. This makes it possible to measure RMS wave heights. An experimental aircraft system for such measurements is discussed. The system utilizes a surface transmitter and an airborne receiver. Questions of high frequency scattering from the ocean surface are considered along with surface spectrum measurements.

Ruck, G. T.↗
NASA NTRS1974

A dual frequency radar for ocean roughness sampling

A microwave technique for determining the roughness (rms wave height) of a randomly varying air-water interface has been developed theoretically, verified with laboratory wavetank studies and is currently being implemented for ocean surface measurements in a series of applications flight experiments. These aircraft observations will be near the Chesapeake Light Tower and will include a range of altitudes and sea conditions. The measurement concept involves cross-correlating the envelope fluctuations on two received carriers that are monochromatic when transmitted in a normal direction to the interface and are observed in a backscatter direction after reflection by the large number of randomly distributed specular points on the surface. The measured correlation coefficient (normalized covariance) as a function of carrier frequency separation will depend on the surface roughness, specifically the probability density function of the specular point height. Details of the flight system are discussed, and preliminary flight results are presented.

Weissman, D. E.↗
NASA NTRS1974

Monitoring the sea surface with a short pulse radar

A solution is presented for the scattering of short pulses from a stochastic, corrugated surface relative to the sea for the case of a narrow-beam transmitting antenna pointing near nadir. The spectrum of the received power and its time history are calculated and this solution is used to show that a measure of the variance of the surface ordinant can be obtained from the backscattered power. Included explicitly in the analysis is the finite nature of the source and the role of the small-scale wave structure (capillary wave range). It is shown that when sufficiently short pulses are transmitted, one can obtain a measure of the variance of the large scale surface ordinant from either the temporal spacing of the peaks in the returned power or from the envelope of the spectrum of the received power. Assuming an appropriate model for the statistics and spectrum of the surface ordinate, the variance can be used to compute the wind speed and the significant wave height of the surface.

Le Vine, D. M.↗
NASA NTRS1975

Satellite altimetry applications

In satellite altimetry the highly stable platform provided by a satellite is utilized as a moving reference system from which vertical measurements to the ocean surface are made. Satellite altimetry applications are related to geoid determination, questions concerning the consideration of local topography, geological-structure studies, investigations regarding the distribution of wave heights, current detection, and the mapping of land topography.

Mcgoogan, J. T.↗
NASA NTRS1977

Mission design for SEASAT-A, an oceanographic satellite

SEASAT-A is a NASA earth satellite for measuring global ocean dynamics from space. Launch is planned for May 1978. The instruments on the spacecraft will provide data on wave height and direction, surface wind speed and direction, ice fields, ocean surface topography and weather. This paper is concerned with the mission design for SEASAT-A. A primary topic here is the selection of the orbit which best satisfies the measurement objectives of the various instruments. The maintenance of this orbit under drag and other perturbations is discussed. The design of the mission profile is outlined. Finally precision orbit determination for SEASAT-A is discussed since it is required to maximize ocean topography accuracy.

Cutting, E.↗
NASA NTRS1977

Short pulse radar used to measure sea surface wind speed and SWH

A joint airborne measurement program is being pursued by NRL and NASA Wallops Flight Center to determine the extent to which wind speed and sea surface significant wave height (SWH) can be measured quantitatively and remotely with a short pulse (2 ns), wide-beam (60 deg), nadir-looking 3-cm radar. The concept involves relative power measurements only and does not need a scanning antenna, Doppler filters, or absolute power calibration. The slopes of the leading and trailing edges of the averaged received power for the pulse limited altimeter are used to infer SWH and surface wind speed. The interpretation is based on theoretical models of the effects of SWH on the leading edge shape and rms sea-surface slope on the trailing-edge shape. The models include the radar system parameters of antenna beam width and pulsewidth.

Hammond, D. L.↗
NASA NTRS1978

Acoustic remote probing of the environment

Atmospheric acoustic probes located either at shore locations near the Chesapeake Bay or on large surface buoys could obtain profiles of wind velocity and turbulence and the temperature and humidity of the atmosphere. At or near the buoy locations, underwater probes located on the bottom could be used to profile current velocity, density, and turbulence and also to determine tide level, wave height, spectrum, and direction. The physical parameter profiles at these earth-surface stations could be used with surface observations by satellite. The most obvious use of data from such a network is to verify and calibrate models of energy exchange between the water of the Bay and the atmosphere.

Pijanowski, J. A.↗
NASA NTRS1978

Seasat-A opens new phase in earth observations

The data output of the Seasat-A, the first satellite designed specifically for oceanographic observation, is described. Wave height and direction, ice distribution, surface wind speed and direction, ocean-surface temperature, and atmospheric water content will be monitored by the satellite. Imaging radar, microwave scatterometer, microwave radiometer and visual and infrared radiometer experiments are included in the Seasat-A observing program. Two types of orbits have been developed: a near-repeat cycle of three days, and a near-repeat cycle of 25 days. Both orbit types offer fine coverage (18.5 km crossing separations) of the earth. Synthetic aperture radar data on computer-compatible tapes and geophysical data records available through the Seasat-A mission are described.

Cutting, E.↗
NASA NTRS1978

Real-time determination of geophysical parameters from a multibeam altimeter

Satellite radar altimeters flown aboard Skylab, GEOS-3 and Seasat-1 have provided a wealth of information on oceanic processes, ice dynamics and geodesy. This paper describes satellite altimetry in its present state and forecasts its future. A brief review of present capability to measure altitude, significant wave height, wind, and current is given. Near term and long range applications are used to indicate desirable technical improvements and an evolutionary plan is presented to develop a sensor to meet future needs. The plan shows a progression from the presently available single-beam terrain profiler to a multibeamed profiling system in the near future which could measure large scale surface slopes without knowing the precise satellite orbit. Ultimately a system would be developed that provides images of height, reflectivity, and target motion. Some of this future system is vividly illustrated by data obtained with the WFC airborne Surface Contour Radar.

Mcgoggan, J. T.↗
NASA NTRS1978

Orbit analysis for Seasat-A

Seasat-A is a NASA earth satellite for measuring global ocean dynamics from space. The instruments on the spacecraft will provide data on wave height and direction, surface wind speed and direction, ice fields, ocean surface topography and atmospheric water content. This paper is concerned with the orbit analysis for Seasat-A. The first topic is the selection of the orbit which best satisfies the measurement objectives of the various instruments. The maintenance of this orbit under drag and other perturbations is also discussed. The second topic is precision orbit determination analysis which is required to achieve ocean topography objectives of the mission.

Cutting, E.↗
NASA NTRS1978

The comparison between the synthetic aperture radar imageries and the surface truth of ocean waves

Ocean waves measured offshore of Marineland, Florida, by the synthetic aperture radar (SAR) are compared with the surface truth data. The Fourier transform of SAR imageries are taken and the corrections of the wave directions and wave lengths due to the relative velocities between SAR and waves are considered. Favorable comparisons are obtained for the peak frequencies, wave directions, and directional distributions. However, the one-dimensional SAR spectra are quite different from the surface truth wave height spectra.

Hsiao, S. V.↗
NASA NTRS1979

Seasat synthetic aperture radar - Ocean wave detection capabilities

A preliminary assessment has been made of the capability of the Seasat synthetic aperture radar to detect ocean waves. Comparison with surface and aircraft measurements from five passes of the satellite over the Gulf of Alaska indicates agreement to within about 15 percent in wavelength and about 25 deg in wave direction. These results apply to waves 100 to 250 meters in length, propagating in a direction predominantly across the satellite track, in sea states with significant wave height in a range of 2 to 3.5 meters.

Gonzalez, F. I.↗