Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “rainfall rate”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Microwave remote sensing: Active and passive. Volume 3 - From theory to applications

Aspects of volume scattering and emission theory are discussed, taking into account a weakly scattering medium, the Born approximation, first-order renormalization, the radiative transfer method, and the matrix-doubling method. Other topics explored are related to scatterometers and probing systems, the passive microwave sensing of the atmosphere, the passive microwave sensing of the ocean, the passive microwave sensing of land, the active microwave sensing of land, and radar remote sensing applications. Attention is given to inversion techniques, atmospheric attenuation and emission, a temperature profile retrieval from ground-based observations, mapping rainfall rates, the apparent temperature of the sea, the emission behavior of bare soil surfaces, the emission behavior of vegetation canopies, the emission behavior of snow, wind-vector radar scatterometry, radar measurements of sea ice, and the back-scattering behavior of cultural vegetation canopies.

Ulaby, F. T.↗
NASA NTRS1985

Seasat microwave wind and rain observations in severe tropical and midlatitude marine storms

Initial results of studies concerning Seasat measurements in and around tropical and severe midlatitude cyclones over the open ocean are presented, together with an assessment of their accuracy and usefulness. Complementary measurements of surface wind speed and direction, rainfall rate, and the sea surface temperature obtained with the Seasat-A Satellite Scatterometer (SASS), the Scanning Multichannel Microwave Radiometer (SMMR), and the Seasat SAR are analyzed. The Seasat data for the Hurrricanes Fico, Ella, and Greta and the QE II storm are compared with data obtained from aircraft, buoys, and ships. It is shown that the SASS-derived wind speeds are accurate to within 10 percent, and the directions are accurate to within 20 percent. In general, the SASS estimates tend to measure light winds too high and intense winds too low. The errors of the SMMR-derived measurements of the winds in hurricanes tend to be higher than those of the SASS-derived measurements.

Black, P. G.↗
NASA NTRS1986

Simultaneous ocean cross section and rainfall measurements from space with a nadir-looking radar

In the case of a nadir-looking spaceborne or aircraft radar in the presence of rain, the return power corresponding to secondary surface scattering may provide information on the properties of the surface and the precipitation. The object of the study is to evaluate a method for determining simultaneously the rainfall rate and the backscattering coefficient of the surface. The method is based upon the mirror-reflected power, which corresponds to the portion of the incident power scattered from the surface to the precipitation, intercepted by the precipitation, and again returned to the surface where it is scattered a final time back to the antenna.

Meneghini, Robert↗
NASA NTRS1987

Conceptual design of a spaceborne radar for global rain mapping

The conceptual design of a spaceborne rain mapping radar is described. This system has dual frequency channels operating at 14 and 35 GHz. It is capable of measuring precepitation profiles for rainfall rates from 0.3 mm/hr and up to 60 mm/hr. The rain reflectivity measurements obtained by this system are expected to have accuracies better than 10 percent.

Im, K. E.↗
NASA NTRS1987

Scattering parameters for aspherical hydrometeors at microwave frequencies

Scattering parameters for ensembles of aspherical ice and liquid hydrometeors were calculated at Psi = 50 deg for frequencies of 37.0, 50.3, and 85.6 GHz. Hydrometeors were assumed to be oblate spheroids whose semiminor axes were aligned at Psi = 0 deg. The angle of 50 deg is determined by the viewing angle of recent satellite-borne radiometers. Backscattering phase functions and extinction coefficients at Psi = 0 deg were also computed at 18.0, 37.0, and 85.6 GHz to provide information for future nadir scanning radars. The hydrometeors were assumed to be characterized by Marshall-Palmer (1948) size distributions. The extended boundary condition method was used to calculate the extinction and backscattering coefficients as well as the albedo for single scattering and the asymmetry factor of the phase function. Results are fitted to simple functions of the rainfall rate. Some comparisons intended to illustrate the differences and similarities of these results with those obtained from equal volume spheres are also presented.

Kummerow, C.↗
NASA NTRS1988

The development of a facility for full-scale testing of airfoil performance in simulated rain

NASA Langley's Aircraft Landing Dynamics Facility has been adapted in order to test the performance of airfoils in a simulated rain environment, at rainfall rates of 2, 10, 30, and 40 inches/hour, and thereby derive the scaling laws associated with simulated rain in wind tunnel testing. A full-scale prototype of the rain-generation system has been constructed and tested for suitable rain intensity, uniformity, effects of crosswinds on uniformity, and drop size range. The results of a wind tunnel test aimed at ascertaining the minimum length of the simulated rain field required to yield an airfoil performance change due to the rain environment are presented.

Taylor, John T.↗
NASA NTRS1988

Determining microwave brightness temperatures from precipitating horizontally finite and vertically structured clouds

Microwave radiances that may be measured from satellite-borne radiometers operating at 37 GHz have been computed as a function of rainfall rates from horizontally finite precipitating clouds that contain both ice and liquid hydrometeors. It is found that precipitating ice at the top of the cloud depresses brightness temperatures significantly. Detailed comparison between finite clouds and the equivalent sections of plane-parallel clouds are made. Footprint averaged brightness temperatures from finite clouds are found to deviate considerably from the sectioned plane-parallel approximation, especially for large rain rates. Better agreement is achieved if a plane-parallel source function is used in the finite cloud model. The effect of shape and orientation of the precipitating cells with respect to the satellite has also been considered. It is found that the largest errors introduced by plane-parallel theory besides the footprint-filling errors are encountered when precipitating cells have large fractions of their surface below the freezing level or contain large amounts of ice.

Kummerow, C.↗
NASA NTRS1988

Effects of rainfall on scatterometer derived wind speeds

Rainfall modification of scatterometer response from the sea surface was simulated in wind-wave tank experiments. Data show that for a given wind speed, radar cross section increases as rainfall rate increases, but this effect decreases as wind speed increases. An empirical model accounts for these observations.

Bliven, L. F.↗
NASA NTRS1988

Thunderstorm ice induced brightness temperature depressions at 18, 37, and 92 GHz during Cohmex and their implications for satellite precipitation retrievals

Measurements of thunderstorm ice scattering at 18, 37, and 92 GHz, and with high spatial and temporal resolution from the Cooperative Huntsville Meterorlogical Experiment (Cohmex) are discussed. The Cohmex experiment consisted of ground-based, airborne, and satellite experiments in June and July, 1986. The rainfall rates from the experiment are compared with other measurements and the implications of the results for satellite precipitation retrievals are examined.

Hood, Robbie E.↗
NASA NTRS1987

Satellite remote sensing of cloud distribution and amount of rainfall over the Tibet Plateau area of China

The use of images from the GOES-1 satellite to study mesoscale convective clouds over the Tibet Plateau region in China is discussed. The correlation between the quantity of rainfall observed at the ground and the cloud volume dissipation per unit area as determined from satellite IR imagery is examined. It is shown that this relationship is almost linear for the rainfall rate exceeding 8 mm/day.

Hung, R. J.↗
NASA NTRS1988

Use of four-dimensional data assimilation by Newtonian relaxation and latent-heat forcing to improve a mesoscale-model precipitation forecast - A case study

The Penn State/NCAR mesoscale model was used to study special static-initialization (SI) and dynamic-initialization (DI) techniques designed to improve short-range quantitative precipitation forecasts (QPFs), as applied to the heavy convective rainfall that occurred in Texas, Oklahoma, and Kansas during the May 9-10, 1979 SESAMY IV study period. In the DI procedure, two types of four-dimensional data assimilation (FDDA) procedures were used to incorporate data during a 12-h preforecast period, one using the Newtonian relaxation, the other using latent-heat forcing. It was found that combined use of either the preforecast or in-forecast latent-heat forcing with the Newtonian relaxation produced an improved forecast (relative to a conventional forecast procedure) of rainfall intensity compared to the use of the Newtonian relaxation alone. The use of the experimental SI with prescribed latent heating during the first forecast hour produced greatly improved rainfall rates.

Wang, Wei↗
NASA NTRS1989

Multiparameter radar study of a microburst - Comparison with model results

Radar observations and model results are used to investigate the microphysical evolution of an isolated, intense storm observed on July 20, 1988 during the Microburst and Severe Thunderstorm experiment. The storm grew to a height of 14 km and upon collapsing, produced heavy rain, pea-sized hail, and a microburst at the surface. The radar observations indicate that the initial precipitation development was by collision-coalescence. As the storm intensified, accretional growth became dominant leading to rapid precipitation development. Radar-derived rainfall rates peaked around 150 to 190 mm/h. Each morning during the experiment, a two-dimensional, time-dependent cloud model, initialized with the morning sounding, was run. The model results from the July 20 sounding are compared to the radar observations. Good agreement is shown in some aspects of the storm development, although the numerical simulation predicted a more vigorous storm than actually developed.

Tuttle, John D.↗
NASA NTRS1988

Airborne rain mapping radar

An airborne scanning radar system for remote rain mapping is described. The airborne rain mapping radar is composed of two radar frequency channels at 13.8 and 24.1 GHz. The radar is proposed to scan its antenna beam over + or - 20 deg from the antenna boresight; have a swath width of 7 km; a horizontal spatial resolution at nadir of about 500 m; and a range resolution of 120 m. The radar is designed to be applicable for retrieving rainfall rates from 0.1-60 mm/hr at the earth's surface, and for measuring linear polarization signatures and raindrop's fall velocity.

Wilson, W. J.↗
NASA NTRS1988

Estimating water flow through a hillslope using the massively parallel processor

A new two-dimensional model of water flow in a hillslope has been implemented on the Massively Parallel Processor at the Goddard Space Flight Center. Flow in the soil both in the saturated and unsaturated zones, evaporation and overland flow are all modelled, and the rainfall rates are allowed to vary spatially. Previous models of this type had always been very limited computationally. This model takes less than a minute to model all the components of the hillslope water flow for a day. The model can now be used in sensitivity studies to specify which measurements should be taken and how accurate they should be to describe such flows for environmental studies.

Devaney, Judy E.↗
NASA NTRS1989

Low elevation angle KU-band satellite measurements at Austin, Texas

At low elevation angles, the propagation of satellite signals is affected by precipitation as well as by inhomogeneties of the refractive index. Whereas precipitation causes fades for relatively small percentages of time, the refractive index variability causes scintillations which can be observed for most of the time. An experiment is now under way in Austin, Texas, in which the right hand circularly polarized 12 GHz beacon of INTELSAT-V/F10 is observed at a 5.8 deg elevation angle, along with the radiometric sky temperature, rainfall rate, humidity, pressure, temperature, and wind speed and direction. The objective of these measurements is to accumulate a database over a period of 2 years and to analyze the probabilities and dynamical behavior of the signal variations in relation to the meteorological parameters. The hardware and software used for the data acquisition and analysis is described and the results from the first year of measurements are presented.

Vogel, Wolfhard J.↗
NASA NTRS1989

Ground data system architecture for precipitation determination from space-based radar

The Tropical Rain Mapping Radar (Tramar) is proposed as an attached payload as part of the Space Station Earth Observing System Program. Tramar would measure rainfall rates, rain velocity, and rain cell areal extent in the latitude band from 30 deg S to 30 deg N for use in studies of large-scale atmospheric circulation, variations of latent heating, tropical hydrologic processes, and mesoscale precipitation systems. The Tramar science requirements, radar design, and ground data system architecture are examined, including the three-dimensional scan geometry, the radar system performance parameters, the production of earth-gridded maps, and the telemetry, sensor, radiometric, and geophysical data that would be obtained by Tramar.

Hilland, Jeffrey E.↗
NASA NTRS1989

Tropical oceanic rainfall - Estimation from SMMR and SSM/I

A method of inferring rainfall over oceans with Nimbus-7 SMMR data (Prabhakara et al., 1986) is improved by including data from the DMSP Special Sensor Microwave Imager (SSM/I). The microwave observations at low frequencies are compared with the SSM/I measurements at 85 GHz. The process used to analyze the microwave data and the retrieval method are described. A map of the monthly mean rainfall rate for July 1987 over the North and South Pacific Oceans is obtained using the SSM/I data.

Prabhakara, C.↗