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At least 595 records · Page 33

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DOE OSTI2020

Data product development for cold cloud and precipitation process analysis/Snow regime classifications from the NSA snow product

This grant funded work focused first on developing a data product for cold-cloud precipitation and second, under a continuation, on examining distinct snowfall regimes occurring at the North Slope Alaska (NSA) facility. The overarching goal under the first phase was to provide a data product that quantifies the vertically- and temporally-resolved properties of cold, precipitating clouds and that will enable future analyses of the processes that control their formation and evolution. The data product derives from observations at the NSA Utqiagvik (BRW) and Oliktok Point (OLI) sites, its algorithm utilizing radar observations supplemented with in situ and other collocated remote sensing measurements to constrain an optimal estimation retrieval.

54 ENVIRONMENTAL SCIENCES↗

NASA NTRS2003

Flood warnings, flood disaster assessments, and flood hazard reduction: the roles of orbital remote sensing

Orbital remote sensing of the Earth is now poised to make three fundamental contributions towards reducing the detrimental effects of extreme floods. Effective Flood warning requires frequent radar observation of the Earth's surface through cloud cover. In contrast, both optical and radar wavelengths will increasingly be used for disaster assessment and hazard reduction.

floods↗

NASA NTRS2003

Flood warnings, flood disaster assessments, and flood hazard reduction : the roles of orbital remote sensing

Orbital remote sensing is now poised to make three fundamental contributions towards reducing the detrimental effects of extreme floods. Effective Flood warning requires frequent (near-daily) radar observation of the Earth's surface through cloud cover. In contrast, both optical and radar wavelengths will increasingly be used for disaster assessment and hazard reduction. These latter tasks are accomplished, in part, by accurate mapping of flooded lands and commonly over periods of several days or more. We use radar scatterometer data from QuikSCAT to detect changes in surface water area and with a full global coverage every 2.5 days. Also, MODIS, RADARSAT, and other higher spatial resolution data are used for flood mapping and other flood measurements. These records are preserved in a global flood hazard atlas at http://www.dartmouth.edu/-floods/Atlas.html.

Shabaneh, Tamer B.↗

NASA NTRS1987

Radar scattering and equilibrium ranges in wind-generated waves with application to scatterometry

To provide theoretical basis for the connection between observed radar scattering and wind-generated waves, a model for the response of surface waves in the gravity-capillary equilibrium region of the spectrum is proposed on the basis of a local (in wavenumber) balance between wind input and dissipation. The wind input function was constructed on the basis of laboratory observations of short-wave growth, while the dissipation function was developed from ideas of viscous dissipation and wave breaking in response to local accelerations and modified by kinematic effects of phase and group velocity differences. The model was exercised at L, C, X, and Ka bands to demonstrate the differences in wind speed and water temperature sensitivity.

Donelan, Mark A.↗

NASA NTRS1981

Viking bistatic radar experiment - Summary of first-order results emphasizing north polar data

Initial results of bistatic radar observations of Mars made by the Viking Orbiter spacecraft are presented with particular emphasis on the previously unstudied polar regions. Bistatic radar scattering experiments were performed in near-equatorial regions by the Viking Orbiter 1, while other regions of the planet were observed by the polar-orbiting Orbiter 2, with scattered signals received by stations of the NASA Deep Space Network. In the equatorial region, the bistatic radar estimates of rms surface slope are found to be in qualitative agreement with results obtained using earth-based transmitter-receivers, showing a nearly 2:1 decrease in rms surface roughness between 20 and 22 deg N with no appreciable change in dielectric constant. Data in the north polar region reveal variations in surface roughness from 1 to 6 deg, with areas of smooth material generally located within rougher environs, surface roughness decreasing along Vastitas Borealis in the direction of the north pole, and north polar cap rms roughnesses on the order of 2.5-3.0 deg. Trends in radar reflectivity suggest a decreasing surface density with increasing latitude, consistent with a layer of seasonal CO2 or H2O snow increasing in depth as the pole is approached.

Simpson, R. A.↗

NASA NTRS1986

SIR-B measurements and modeling of vegetation

A summary is presented of the results derived from analysis of six SIR-B data takes over an agricultural test site in west central Illinois. The first part describes the procedure used to calibrate the SIR-B imagery, the second part pertains to the observed radar response to soil moisture content, and the last part examines the information derivable from multiangle observations.

Ulaby, Fawwaz T.↗

NASA NTRS1992

Comparison of Goldstone and Magellan radar data in the equatorial plains of Venus

Goldstone radar observations of the equatorial plains of Venus provide complementary information to that obtained by Magellan. Different radar scattering mechanisms dominate each system, leading to sampling of different surface properties. Comparison of image data and derived parameters indicate that: (1) relatively high dielectric constants on impact-related parabolic features are detected in Goldstone backscatter, Magellan reflectivity, and Magellan emissivity data; the dielectric effects are overwhelmed by roughness-related signatures in Magellan synthetic aperture radar (SAR) data; (2) lava flows in Navka Planitia show dielectric variations both among and within flows; higher dielectric constants on the perimeter of some flows may by due to a decrease in vesicularity; (3) some volcanic domes are relatively smooth at the wavelength scale and probably consist of low-density deposits; (4) comparisons of Magellan SAR data with rough surface scattering models and SAR data of terrestrial surfaces indicate that the roughness characteristics of the equatorial plains surfaces are comparable to modified terrestrial lava flows; and (5) scattering properties of an equatorial 'ridge belt' structure suggest highly weathered or soil-dominated surfaces.

Plaut, Jeffrey J.↗

NASA NTRS1991

Remote sensing of precipitation structures using combined microwave radar and radiometric techniques

After reviewing published multiparameter radar observations and their interpretation for microphysical retrieval, the paper presents radiative transfer model simulations performed using radar measurements and a cloud model. The qualitative and quantitative aspects of the remote sensing of precipitation are discussed with particular attention given to the potential of estimating scattering-based ice water path.

Vivekanandan, J.↗

NASA NTRSDate not supplied

Simulating Microwave and Radar Signals in Severe Weather Conditions

The development of radiative transfer simulators for radar and microwave signals, spanning a range of frequencies from 10 to 800 GHz, is paramount for enhancing weather forecasting accuracy, particularly for severe weather events. These tools facilitate the assimilation of microwave and radar observations into numerical weather prediction models, thereby improving accuracy of weather forecasts. Additionally, they directly simulate radar signals crucial for autonomous vehicle operation, with frequencies commonly used in radar systems such as 24, 74, 77, and 79 GHz. However, these frequencies are susceptible to weather phenomena like severe rain and snow, which can significantly impact vehicle safety and performance. These simulation tools, including radiative transfer simulators, serve a dual purpose. Firstly, they enhance forecasts for severe weather events, contributing to autonomous vehicle safety by providing early warnings and risk assessments. Secondly, they enable the direct simulation of radar signals in autonomous vehicle driving systems, allowing researchers and engineers to evaluate radar system performance under various weather conditions. In addition to the radar signal simulator, this abstract discusses the incorporation of advanced scattering properties developed using the discrete dipole approximation (DDA). The DDA technique enhances scattering calculations for frozen hydrometeors at microwave frequencies, thereby improving the accuracy of radar signal simulations and enabling more accurate assessments of radar system performance in adverse weather conditions. In summary, this abstract explores the development and utilization of comprehensive simulation tools, emphasizing their significance in simulating microwave and radar signals and improving weather forecasts. Special attention is given to the simulation of radar signals at critical frequencies for autonomous vehicle sensing and navigation, addressing challenges posed by severe weather phenomena and their effects on signal propagation and detection

Isaac Moradi↗

NASA NTRS1991

Io's radar properties

Arecibo 13 cm wavelength radar observations during 1987-90 have yielded echoes from Io on each of 11 dates. Whereas Voyager imaged parts of the satellite at resolutions of several km and various visible/infrared measurements have probed the surfaces's microscale properties, the radar data yield new information about the nature of the surface at cm to km scales. Our observations provide fairly thorough coverage and reveal significant heterogeneity in Io's radar properties. A figure is given showing sums of echo spectra from 11 dates.

Ostro, Steven J.↗

NASA NTRS2012

High Resolution Observations of Drop Size Distribution for GPM Ground Validation

During the Mid-latitude Continental Convective Cloud Experiment (MC3E), NASA's GPM GV Disdrometer and Radar Observations of Precipitation (DROP) Facility deployed an array of disdrometers and rain gauges in northern Oklahoma to sample, with high resolution, the drop size distribution for use in development of precipitation retrieval algorithms for the GPM core satellites. The DROP Facility instruments deployed during MC3E consisted of 16 autonomous Parsivel units, 5 two-dimensional video disdrometers (2dvds), a vertically pointing K band radar, and 32 tipping bucket rain gauges. There were several rainfall events during MC3E in which rain drops exceeding 6 mm in diameter were recorded. The disdrometer array revealed large rain drops with diameters exceeding 6 mm and 8 mm during two separate stratiform and convective rainfall events, respectively. The NPOL radar, which was scanning in high resolution RHI mode (every 40 sec) over the disdrometer array during the stratiform event, indicated a 1 km thick bright band with a differential reflectivity column of 2-3 dB extending below the melting layer to the surface where the large drops were recorded by the 2dvds. These large drops are important for GPM since they can have a great impact upon satellite precipitation retrieval, especially near the ground and below heavy convective rainfall cores where satellites have had problems depicting the rainfall.

Gatlin, Patrick N.↗

NASA NTRS2023

Impacts of Marine Surface Pressure Observations From A Spaceborne Differential Absorption Radar Investigated With an Observing System Simulation Experiment

A new instrument has been proposed for measuring surface air pressure over the marine surface with a combined active/passive scanning multi-channel differential absorption radar (DAR) to provide an estimate of the total atmospheric column oxygen content. A demonstrator instrument, the Microwave Barometric Radar and Sounder (MBARS), has been funded by the National Aeronautics and Space Administration (NASA) for airborne test missions. Here, a proof-of-concept study to evaluate the potential impact of spaceborne surface pressure data on numerical weather prediction is performed using the Goddard Modeling and Assimilation Office global observing system simulation experiment (OSSE) framework. This OSSE framework employs the Goddard Earth Observing System model and the hybrid 4D ensemble variational Gridpoint Statistical Interpolation data assimilation system. Multiple flight and scanning configurations of potential spaceborne orbits are examined. Swath width and observation spacing for the surface pressure data are varied to explore a range of sampling strategies. For wider swaths, the addition of surface pressures reduces the root mean square surface pressure analysis error by as much as 20% over some ocean regions. The forecast sensitivity observation impact tool estimates impacts on the Pacific Ocean basin boundary layer 24-hour forecast temperatures for spaceborne surface pressures on par with rawinsondes and aircraft, and greater impacts than the current network of ships and buoys. The largest forecast impacts are found in the southern hemisphere extratropics.

N.C. Privé↗

NASA NTRS1994

Radar aperture synthesis observations of asteroids

We report of Goldstone-VLA, radar aperture-synthesis observations of the mainbelt asteroids 324 Bamberga and 7 Iris and the near-Earth asteroids 1991 EE and 4179 Toutatis. Simultaneous resolution of echoes in both angle and Doppler frequency provide new constraints on the mainbelt asteroids' pole directions: Bamberga's spin vector is within 40 deg of the south ecliptic pole, and the twofold ambiguity in Iris' pole direction (P. Magnusson, 1989) is resolved in favor of the ecliptic coordinates lambda = 15 deg, beta = +25 deg. For Bamberga, monostatic and bistatic radar echoes and VLA thermal-emission measurements, also reported here, are consistent with radiometric estimates of Bamberga's size and with the hypothesis that the asteroid is overlain by a regolith having a porosity of approximately 50%. Our near-Earth asteroid measurements required the development of new on-line VLA software that allows imaging of objects that are in the telescope's `near field.' This software has been successfully tested on Toutatis at a distance of 0.06 AU and will be essential for VLA observations of Earth-approaching comets.

De Pater, Imke↗

NASA NTRS1975

Physical and dynamical studies of meteors. Meteor-fragmentation and stream-distribution studies

Population parameters of 275 streams including 20 additional streams in the synoptic-year sample were found by a computer technique. Some 16 percent of the sample is in these streams. Four meteor streams that have close orbital resemblance to Adonis cannot be positively identified as meteors ejected by Adonis within the last 12000 years. Ceplecha's discrete levels of meteor height are not evident in radar meteors. The spread of meteoroid fragments along their common trajectory was computed for most of the observed radar meteors. There is an unexpected relationship between spread and velocity that perhaps conceals relationships between fragmentation and orbits; a theoretical treatment will be necessary to resolve these relationships. Revised unbiased statistics of synoptic-year orbits are presented, together with parallel statistics for the 1961 to 1965 radar meteor orbits.

Sekanina, Z.↗

NASA NTRS1992

In situ observations of temperature microstructure above and below the tropopause

The small-scale (less than 1 km) structure of temperature near the tropopause, as indicated by ozone concentration, is examined using data recorded during GALE from the NCAR Sabreliner. A systematic difference is observed in the temperature microstructure of the troposphere and stratosphere in qualitative agreement with evidence from VHF radar observations. Spectral distribution of the temperature variations also differs across the tropopause.

Salathe, Eric P., Jr.↗

NASA NTRS2006

Summary of Sessions: Ionosphere - Thermosphere - Mesosphere Working Group

The topics covered by the sessions under the working group on Ionosphere-Thermosphere-Mesosphere dealt with various aspects of the response of the ionosphere-thermosphere coupled system and the middle atmosphere to solar variability. There were four plenary talks related to the theme of this working group, thirteen oral presentations in three sessions and six poster presentations. A number of issues related to effects of solar variability on the ionosphere-thermosphere, observed using satellite and ground-based data including ground magnetometer observations, radio beacon studies of equatorial spread F, and modeling of some of these effects, were discussed. Radar observations of the mesosphere-lower thermosphere region and a future mission to study the coupling of thunderstorm processes to this region, the ionosphere, and magnetosphere were also presented.

Spann, J. F.↗

NASA NTRS2016

Using a Multiwavelength Suite of Microwave Instruments to Investigate the Microphysical Structure of Deep Convective Cores

Due to the large natural variability of its microphysical properties, the characterization of solid precipitation is a longstanding problem. Since in situ observations are unavailable in severe convective systems, innovative remote sensing retrievals are needed to extend our understanding of such systems. This study presents a novel technique able to retrieve the density, mass, and effective diameter of graupel and hail in severe convection through the combination of airborne microwave remote sensing instruments. The retrieval is applied to measure solid precipitation properties within two convective cells observed on 2324 May 2014 over North Carolina during the IPHEx campaign by the NASA ER-2 instrument suite. Between 30 and 40 degrees of freedom of signal are associated with the measurements, which is insufficient to provide full microphysics profiling. The measurements have the largest impact on the retrieval of ice particle sizes, followed by ice water contents. Ice densities are mainly driven by a priori assumptions, though low relative errors in ice densities suggest that in extensive regions of the convective system, only particles with densities larger than 0.4 gcm3 are compatible with the observations. This is in agreement with reports of large hail on the ground and with hydrometeor classification derived from ground-based polarimetric radars observations. This work confirms that multiple scattering generated by large ice hydrometeors in deep convection is relevant for airborne radar systems already at Ku band. A fortiori, multiple scattering will play a pivotal role in such conditions also for Ku band spaceborne radars (e.g., the GPM Dual Precipitation Radar).

remote sensing retrievals↗

NASA NTRS1989

Viking landing sites, remote-sensing observations, and physical properties of Martian surface materials

Consideration is given to the relations between the physical properties of the surface materials at Viking landing sites, the physical properties of other Martian surfaces inferred from radar observations from earth and thermal observations from orbit, and the geological processes that formed the materials and shaped the surfaces. The radar and thermal remote-sensing signatures of the landing site surface materials are estimated and compared with the thermal and radar measurements for the entire planet. It is shown that the surface materials at the landing sites are good analogs for the materials in most of the Martian equatorial regions.

Moore, Henry J.↗