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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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NASA NTRS1990

Analysis and improved design considerations for airborne pulse Doppler radar signal processing in the detection of hazardous windshear

High resolution windspeed profile measurements are needed to provide reliable detection of hazardous low altitude windshear with an airborne pulse Doppler radar. The system phase noise in a Doppler weather radar may degrade the spectrum moment estimation quality and the clutter cancellation capability which are important in windshear detection. Also the bias due to weather return Doppler spectrum skewness may cause large errors in pulse pair spectral parameter estimates. These effects are analyzed for the improvement of an airborne Doppler weather radar signal processing design. A method is presented for the direct measurement of windspeed gradient using low pulse repetition frequency (PRF) radar. This spatial gradient is essential in obtaining the windshear hazard index. As an alternative, the modified Prony method is suggested as a spectrum mode estimator for both the clutter and weather signal. Estimation of Doppler spectrum modes may provide the desired windshear hazard information without the need of any preliminary processing requirement such as clutter filtering. The results obtained by processing a NASA simulation model output support consideration of mode identification as one component of a windshear detection algorithm.

Lee, Jonggil↗

NASA NTRS1991

Wind abrasion on Mars

Aeolian activity was predicted for Mars from earth based observations of changing surface patterns that were interpreted as dust storms. Mariner 9 images showed conclusive evidence for aeolian processes in the form of active dust storms and various aeolian landforms including dunes and yardangs. Windspeeds to initiate particle movement are an order of magnitude higher on Mars than on Earth because of the low atmospheric density on Mars. In order to determine rates of abrasion by wind blown particles, knowledge of three factors is required: (1) particle parameters such as numbers and velocities of windblown grains as functions of windspeeds at various heights above the surface; (2) the susceptibility to abrasion of various rocks and minerals; and (3) wind frequencies and speeds. For estimates appropriate to Mars, data for the first two parameters can be determined through lab and wind tunnel tests; data for the last two factors are available directly from the Viking Lander meteorology experiments for the two landing sites.

Greeley, Ronald↗

NASA NTRS1991

Free convection in the Martian atmosphere

Researchers investigated the free convective regime for the Martian atmospheric boundary layer (ABL). Researchers generalized Schumann's model describing horizontal fluctuations and mean vertical gradients occurring during free convection to include convection driven by water vapor gradients and to include the effects of circulation above both aerodynamically smooth and rough surfaces. Applying the model to Mars, researchers found that nearly all the resistance to sensible and latent heat transfer in the ABL occurs within the thin interfacial sublayer at the surface. Free convection is found to readily occur at low pressures and high temperatures when surface ice is present. At 7 mb, the ABL should freely convect whenever the mean windspeed at the top of the surface layer drops below about 2.5 m s(-1) and surface temperatures exceed 250 K. Mean horizontal fluctuations within the surface layer are found to be as high as 3 m (-1) for windspeed, 0.5 K for temperature, and 10 (-4) kg m (-3) for water vapor density. Airflow over surfaces similar to the Antarctic Polar Plateau was found to be aerodynamically smooth on Mars during free convection for all pressures between 6 and 1000 mb, while surfaces with z sub o approx. equals 1 cm are aerodynamically rough over this pressure range.

Clow, G. D.↗

NASA NTRS2008

Two Empirical Models for Land-falling Hurricane Gust Factors

Gaussian and lognormal models for gust factors as a function of height and mean windspeed in land-falling hurricanes are presented. The models were empirically derived using data from 2004 hurricanes Frances and Jeanne and independently verified using data from 2005 hurricane Wilma. The data were collected from three wind towers at Kennedy Space Center and Cape Canaveral Air Force Station with instrumentation at multiple levels from 12 to 500 feet above ground level. An additional 200-foot tower was available for the verification. Mean wind speeds from 15 to 60 knots were included in the data. The models provide formulas for the mean and standard deviation of the gust factor given the mean windspeed and height above ground. These statistics may then be used to assess the probability of exceeding a specified peak wind threshold of operational significance given a specified mean wind speed.

Merceret, Franics J.↗

NASA NTRSDate not supplied

Derivation and Testing of Consumptive Water Use Fraction for Specialty Crops

The Crop Consumptive Use Fraction (CCUF) expresses beneficial water use in the form of seasonal evapotranspiration of applied water (ETAW), relative to total irrigation volume. The metric is an indicator of the efficiency of agricultural water use and is a recommended component for preparation of agricultural water management plans in California. An FAO-56 based web application has been developed to facilitate retrospective evaluation of ETAW, and hence CCUF, at field level. The current application is optimized for prevailing climate in four of the state’s main growing regions: San Joaquin Valley, Sacramento Valley, Central Coast, and North Coast. User inputs include crop type, soil texture, irrigation method, daily irrigation volume, daily rainfall, and seasonal start/stop dates to define the analysis period. Time series of fractional green canopy cover (Fc), based on Landsat and Sentinel-2 Earth-resource satellite observations, are imported from NASA’s Satellite Irrigation Management Support (SIMS) system. Grass reference evapotranspiration (ETo) time series are accessed from Spatial CIMIS (California Irrigation Management Information System). Daily crop height (h) is estimated as a simple function of typical maximum height for the given crop type (from FAO-56) and Fc. A vegetation density coefficient (Kd) is derived from Fc and h. Stomatal control factors during mid-and late-season are applied to tree and vine crops. Typical values for minimum daily relative humidity and mean daily windspeed, derived from historical CIMIS weather data, are used to correct for regional deviations from standard climate (defined as RHmin=45%, windspeed =2m/s). The resulting daily basal crop coefficient (Kcb) represents the ET of a well-watered crop with minimal soil evaporation, relative to ETo. A soil water balance sub-model for the top 0.1 m is used to calculate daily evaporation coefficients (Ke). A second sub-model applies to the root zone to calculate crop water stress coefficients (Ks) and effective precipitation (Pe), which is the fraction of rainfall that is available for crop use. Those coefficients are combined with Kcb and ETo to calculate daily ETc. ETAW is then derived as cumulative ETc less cumulative Pe. For verification purposes, sensor installations were used to measure seasonal ETc in commercial fields for several annual and perennial specialty crops by soil water balance and energy balance methods. Model estimates of seasonal ETc show mean absolute error of <10% compared to the ground measurements.

Derivation↗

NASA NTRS1974

Preliminary analysis of Skylab RADSCAT results over the ocean

Preliminary observations at 13.9 GHz of the radar backscatter and microwave emission from the sea were analyzed using data obtained by the radiometer scatterometer on Skylab. Results indicate approximately a square-law relationship between differential scattering coefficient and windspeed at angles of 40 deg to 50 deg, after correction for directional effect, over a range from about 4 up to about 25 meters/sec. The brightness temperature response was also observed, and considerable success was achieved in correcting it for atmospheric attenuation and emission. Measurements were made in June, 1973, over Hurricane Ava off the west coast of Mexico and over relatively calm conditions in the Gulf of Mexico and Caribbean Sea.

Moore, R. K.↗

NASA NTRS1975

Wind tunnel investigation of helicopter-rotor wake effects on three helicopter fuselage models

The effects of rotor wake on helicopter fuselage aerodynamic characteristics were investigated in the Langley V/STOL tunnel. Force, moment, and pressure data were obtained on three fuselage models at various combinations of windspeed, sideslip angle, and pitch angle. The data show that the influence of rotor wake on the helicopter fuselage yawing moment imposes a significant additional thrust requirement on the tail rotor of a single-rotor helicopter at high sideslip angles.

Wilson, J. C.↗

NASA NTRS1974

Simultaneous active and passive microwave response of the earth - The Skylab radscat experiment

The Skylab microwave radiometer-scatterometer experiment S-193 was designed to collect simultaneous information on the radiometric emission and the backscatter from the earth from orbital altitude for the first time. A primary driving force was ascertaining the response from the oceans of both active and passive systems to variations in wind, and the ability of the passive system to aid in calibrating the active system. Numerous overland applications were also explored. Preliminary results of backscatter and emission from sea and atmosphere are shown for hurricane Ava and for two flights across the Gulf of Mexico. The results tend to confirm the most recent theoretical prediction of an approximately square-law relation between scattering coefficient for horizontal polarization and windspeed, with a somewhat smaller dependence for vertical polarization. Overland measurements show that scatterometer signals at 30 deg increase and radiometer signals decrease for terrain that has recently experienced rainfall.

Moore, R. K.↗

NASA NTRS1977

On the hysteresis of the sea surface and its applicability to wave height predictions

Because of the low dissipation rate of wave energy on the ocean's surface, the wave height at some location and time must be dependent upon wind fields in existence there at previous times and upon swell propagated there from other regions. To study these relationships, significant wave height (SWH) measurements from the Geos-3 radar altimeter are used in conjunction with anemometer windspeed measurements from weather ships, L, C, and R. During the passage of large cyclonic disturbances near the fixed locations of these vessels in the North Atlantic in February 1976, distinct hysteresis profiles that characterize the sea's memory during generation and dissipation conditions are observed. Examples are given that demonstrate the influences of cyclone intensity, movement, velocity, and shape on the configuration of these profiles.

Parsons, C. L.↗

NASA NTRS1980

Liquid solar collector

Report documents evaluation test on commercial flat-plate solar collector that uses water as working fluid. Performance was measured before and after 34-day exposure to natural environment. Tables in metric and English units present data on air and water temperatures, waterflow, insolation, efficiency, and windspeed and direction.

Source record↗

NASA NTRS1980

Collector performance at various air-channel depths

Report describes evaluation of solar collector efficiency which was measured at airflow channel depths of 3, 2, 1, and 1/2 inches in solar simulator. Data were also recorded on absorber surface temperature, inlet and outlet temperatures, airflow and insolation rates, collector differential pressure and windspeed, for result tabulation and plotting.

Source record↗

NASA NTRS1980

Weathering of a flat-plate solar collector

Report contains performance evaluation of flat-plate liquid solar collector after 14-months of natural weathering. Collector efficiency was calculated and plotted as function of inlet liquid temperature. Measurements were made of ambient temperature, inlet and outlet temperatures, differential temperature and pressure, liquid flow rate, insolation, and windspeed.

Source record↗

NASA NTRS1980

Weathering of a liquid solar collector

Commercially available flate plate hot water solar collector is characterized in report that presents 10 month weathering study of system. Collector efficiency was calculated and plotted from measurements of fluid temperature and flow rate, ambient temperature and solar flux. Windspeed and wind direction were also measured during tests.

Source record↗

NASA NTRS1979

Measurement of hurricane winds and waves with a synthetic aperture radar

An analysis of data collected in a hurricane research program is presented. The data were collected with a Synthetic Aperture Radar (SAR) during five aircraft flights in the Atlantic in August and September, 1976. Work was conducted in two areas. The first is an analysis of the L-band SAR data in a scatterometer mode to determine the surface windspeeds in hurricanes, in a similar manner to that done by an X-band scatterometer. The second area was to use the SAR to examine the wave patterns in hurricanes. The wave patterns in all of the storms are similar and show a marked radial asymmetry.

Shemdin, O. H.↗

NASA NTRS1979

A scheme for computing surface fluxes from mean flow observations

A computational method for estimating turbulent surface stress, sensible heat flux, and humidity flux from mean velocity, temperature, and humidity at a single height in the atmospheric surface layer is presented. The method is based on coupling a Monin-Obukhov similarity profile to a 'force-restore' formulation for the evolution of surface soil temperature to yield the local values of shear stress, heat flux, and surface temperature. In addition to reference-level mean flow properties, the parameters required to implement this method are the thermal heat capacity of the soil, the surface aerodynamic roughness, latitude, solar declination, surface albedo, surface emissivity, and atmospheric transmissivity. Sample calculations are presented for (1) constant atmospheric forcing at the reference level, and (2) variable atmospheric forcing corresponding to Kahle's (1977) measurements of windspeed, air temperature, and radiometer soil surface temperature under dry vegetatively sparse conditions in the Mohave Desert, Calif.

Hoffert, M. I.↗

NASA NTRS1979

The effect of the sea breeze circulation on surface ozone levels at Wallops Island, Virginia

Surface measurements of windspeed, direction, and ozone concentration collected at Wallops Island, Virginia, during the summers of 1977 and 1978 are analyzed to study the effects of the dominant mesoscale sea breeze circulation on the local photochemical oxidant levels. A bimodality in the atmospheric dynamics is linked to systematic variations in ozone concentration. It is concluded that during certain phases of the two circulation modes, increased wind speed reduces the resistance of the earth's surface to the deposition of ozone, and decreased ozone concentration levels result. For other phases, light winds occur, signifying high resistance to deposition and high ozone levels. This modulation by the local dynamics is a major impediment for pollutant studies in coastal environments, especially those centering on transport, because it tends to mask other processes that may be occurring.

Parsons, C. L.↗

NASA NTRS1980

Passive microwave remote sensing of the ocean - A review

This paper reviews the current status of passive microwave remote sensing of the ocean. The physics of emission and instrumentation are highlighted in order to establish a relationship between the thermal emission and retrieved geophysical parameters. A discussion then follows on measurements of temperature, salinity, windspeed, etc. using passive microwave systems. These measurements are related to the accuracy and spatial resolution required by the users. The status of passive microwave remote sensing is summarized and recommendations for future research are presented.

Swift, C. T.↗

NASA NTRS1982

New Energy-Saving Technologies Use Induction Generators

Two energy-saving technologies tested recently at Marshall Space Flight Center use an induction motor operated in reverse (as an induction generator). In the first, energy ordinarily dissipated during load testing of machinery is recovered and returned to powerline. In the second, efficiency of wind-driven induction generator is improved, and useful range of windspeed is broadened. Both technologies take advantage of ac voltage developed across terminals of an induction motor when rotated at higher than-synchronous speed in the direction it normally turns when power is appled.

Nola, F.↗