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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Doppler radar study of the anvil region associated with a squall line

A method for analyzing multiple Doppler radar data is briefly described. A feature of this method is a new automated objective unfolding scheme which unfolds Doppler velocities for all the radars simultanceously rather than one radar at a time. The method has been used to study a region of widespread precipitation trailing a squall line (anvil), using tripple Doppler radar data to calculate horizontal winds, divergence, and vertical air velocity over an area 120 km by 120 km by 9 km deep. The method yields vertical profiles of divergence which verify the extended VAD method results of Matejka and Srivastava (1981) for the same anvil, and provides a more detailed picture of the variation of winds, divergence, and vertical air velocity in the anvil behind the squall line.

Srivastava, R. C.↗
NASA NTRS1986

Wind profiler data in a mesoscale experiment from a meteorological perspective

During May and June of 1985, the Oklahoma-Kansas Preliminary Regional Experiment of STORM-Central (OK PRE-STORM) was carried out, with the major objectives of learning more about mesoscale convective systems (MCSs) and gaining experience in the use of new sensing systems and measurement strategies that will improve the design of STORM-Central. Three 50-MHz wind profilers were employed in a triangular array with sides about 275 km. It is far too soon to report any results of this effort, for it has barely begun. The purpose here is to show some examples of the data, some of the surrounding conventional data, and to discuss some of the issues important to meteorologists in evaluating the contribution of the profiler data. The case of 10 to 11 June 1985, featuring a major squall line system which crossed the dense observing network from northwest to southeast, passing the Liberal site about 2230 GMT/10 June, the McPherson site about 0100 GMT/11 June, and Wichita about 0300 GMT/11 June is discussed. Radar and satellite data show that the system was growing rapidly when it passed Liberal, and was large and mature when it passed through McPherson and Wichita. The radar depiction of the system during this stage is given, with the McPherson site in the intense convective echoes near the leading edge at 01 GMT and in the stratiform precipitation at 03 GMT. The profiler wind data for a 9-hour period encompassing the squall line passage at each site are given.

Zipser, E. J.↗
NASA NTRS2011

Development of the NASA High-Altitude Imaging Wind and Rain Airborne Profiler

The scope of this paper is the development and recent field deployments of the High-Altitude Imaging Wind and Rain Airborne Profiler (HIWRAP), which was funded under the NASA Instrument Incubator Program (IIP) [1]. HIWRAP is a dual-frequency (Ka- and Ku-band), dual-beam (300 and 400 incidence angles), conical scanning, Doppler radar system designed for operation on the NASA high-altitude (65,000 ft) Global Hawk Unmanned Aerial System (UAS). It utilizes solid state transmitters along with a novel pulse compression scheme that results in a system with compact size, light weight, less power consumption, and low cost compared to radars currently in use for precipitation and Doppler wind measurements. By combining measurements at Ku- and Ka-band, HIWRAP is able to image winds through measuring volume backscattering from clouds and precipitation. In addition, HIWRAP is also capable of measuring surface winds in an approach similar to SeaWinds on QuikScat. To this end, HIWRAP hardware and software development has been completed. It was installed on the NASA WB57 for instrument test flights in March, 2010 and then deployed on the NASA Global Hawk for supporting the Genesis and Rapid Intensification Processes (GRIP) field campaign in August-September, 2010. This paper describes the scientific motivations of the development of HIWRAP as well as system hardware, aircraft integration and flight missions. Preliminary data from GRIP science flights is also presented.

Li, Lihua↗
NASA NTRS1980

High-altitude resolution stratospheric measurements with the Arecibo 430-MHz radar

Instrumental modification at the Arecibo Observatory are described, which make possible a resolution of 150 m, the maximum allowed by the transmitter bandwidth. Attention is given to digital decoding, the radar controller, and the fact that a complementary coded pulse scheme generating no pulse side lobes has been used for the first time. It is noted that power spectra of the signals corresponding to 256 altitudes are evaluated on line by means of an array processor. A profile of the E-W component of the wind as a function of altitude has been observed, as well as the discrete layered structure of turbulence, especially at higher altitudes; in addition, the maximum range at which an echo has been detected is about 31 km. The results obtained show the importance for stratospheric studies of high resolution when using radar to obtain wind information from the Doppler shift of turbulence echoes.

Woodman, R. F.↗
NASA NTRS1986

An evaluation of errors observed in the measurement of low wind velocities

Measurements of low wind velocities (the absolute value of V sub H is approx. equal to 6 m/s) with a VHF wind profiler can be difficult if ground clutter or other biases in the system dominate in altering the position of the perceived peak in the calculated power spectrum. A variety of methods for ground clutter suppression are used in profiler systems today (Cornish, 1983). An editing method called zero suppression takes the spectral value of selectable number of points (N) on each side of 0 velocity (one point on either side, in this study) and sets them equal to the mean value of the points exterior to the specified N points on either side of 0. Analysis done with the PSU VHF(1) radar, shows that this zero-suppression method can systematically bias horizontal wings V sub H below 6 m/s. With the zero suppression, an artificial increase in absolute wind velocities occurs when the spectral peaks fall within the plus or minus N points of the FFT (personal communication, Strauch, 1985). It was also established that the method artificially decreases the absolute wind velocities inferred from spectral peaks that are outside but near the suppressed region. Comparisons of wind profiles observed with and without zero suppression are given. The range of the biased velocities extends to about plus or minus 6 m/s. Biases have been deduced to be as much as 2 m/s, but more commonly they are on the order of 1.0 m/s.

Williams, S. R.↗
NASA NTRS1973

Surface features on Mars: Ground-based albedo and radar compared with Mariner 9 topography

Earth-based albedo maps of Mars were compared with Mariner 9 television data and ground-based radar profiles to investigate the nature of the bright and dark albedo features. Little correlation was found except at the boundaries of classical albedo features, where some topographic control is indicated. Wind-blown dust models for seasonal and secular albedo variations are supported, but it is not clear whether the fines are derived from bright or dark parent rock. Mars, like the Earth and Moon, has probably generated two distinct types of crustal material.

Frey, H.↗
NASA NTRS2002

Convection and Easterly Waves Observed in the Eastern Pacific ITCZ During EPIC2001

During the last three weeks of September 2001, the East Pacific Investigation of Climate Processes in the Coupled Ocean-Atmosphere System (EPIC2001) intensive field campaign focused on studies of deep convection in the ITCZ-cold tongue complex over the Mexican warm-pool region (10 deg. N 95 deg. W) of the eastern Pacific Ocean. Major observational platforms deployed during this phase of EPIC2001 included two ships, the NOAA R/V Ronald H. Brown and the NSF R/V Horizon, and two research aircraft including a NOAA P-3 and the NCAR C-130. This study utilizes new C-band Doppler radar and sounding observations collected aboard the R/V Ronald Brown to describe the 4-D structure of ITCZ convection as a function of the environmental forcing and phase of 3-5 day easterly wave passages. Three distinct easterly wave passages occurred during EPIC2001. Each wave originated in the eastern Atlantic Ocean and after moving over Central America and into the eastern Pacific, were easily identified in time-height profiles of wind and thermodynamic data collected at the position of the R/V Brown. In all cases, the wave trough axes (as defined by changes in the meridional and zonal wind direction and changes in pressure altitude) exhibited relatively weak shear at low to mid-levels and tilted westward with height. The humidity profile in each wave did not exhibit as great a tilt in the vertical as the trough axes. Consistent with previous studies of westward tilting waves over the western Pacific Ocean, peaks in radar diagnosed rainfall tended to lead the passage of the surface wave trough by 0-2 days.

Petersen, Walter A.↗
NASA NTRS1988

Studies of high latitude mesospheric turbulence by radar and rocket. II - Measurements of small scale turbulence

Measurements of mesospheric small scale turbulence and associated larger scale wave structures were obtained from rocket probe flights during equinox in spring 1985. The measurements were verified by data from the mesosphere-stratosphere-troposphere radar at Poker Flat, Alaska. Electron density irregularities down to an altitude of about 62 km and fluctuations in positive ion density in the altitude region from 50 to 90 km were measured. Turbulence in the inertial subrange was observed at heights where the fluctuations generally were largest. Measurement of background electron density exhibited gradients relative to the monotonically increasing density profile, suggesting the presence of large amplitude wave motions transporting the plasma by mixing. The radar detected the occurrence of 1-3 km wavelike perturbations superimposed on a 7-km wave in the wind velocity field. It is suggested that the 1-3 km waves are more important in the transport of energy and momentum and in the production of turbulence in the lower mesosphere.

Blood, S. P.↗
NASA NTRS2006

The Dryline on 22 May 2002 during IHOP_2002: Convective-Scale Measurements at the Profiling Site

A detailed analysis of the structure of a double dryline observed over the Oklahoma panhandle during the first International H2O Project (IHOP_2002) convective initiation (CI) mission on 22 May 2002 is presented. A unique and unprecedented set of high temporal and spatial resolution measurements of water vapor mixing ratio, wind, and boundary layer structure parameters were acquired using the National Aeronautics and Space Administration (NASA) scanning Raman lidar (SRL), the Goddard Lidar Observatory for Winds (GLOW), and the Holographic Airborne Rotating Lidar Instrument Experiment (HARLIE), respectively. These measurements are combined with the vertical velocity measurements derived from the National Center for Atmospheric Research (NCAR) Multiple Antenna Profiler Radar (MAPR) and radar structure function from the high-resolution University of Massachusetts frequency-modulated continuous-wave (FMCW) radar to reveal the evolution and structure of the late afternoon double-dryline boundary layer. The eastern dryline advanced and then retreated over the Homestead profiling site in the Oklahoma panhandle, providing conditions ripe for a detailed observation of the small-scale variability within the boundary layer and the dryline. In situ aircraft data, dropsonde and radiosonde data, along with NCAR S-band dual-polarization Doppler radar (S-Pol) measurements, are also used to provide the larger-scale picture of the double-dryline environment. Moisture and temperature jumps of about 3 g kg(sup -1) and 1 -2 K, respectively, were observed across the eastern radar fine line (dryline), more than the moisture jumps (1-2 g kg(sup -1)) observed across the western radar fine line (secondary dryline). Most updraft plumes observed were located on the moist side of the eastern dryline with vertical velocities exceeding 3 m s(sup -1) and variable horizontal widths of 2-5 km, although some were as wide as 7-8 km. These updrafts were up to 1.5 g kg(sup -1) moister than the surrounding environment. Although models suggested deep convection over the Oklahoma panhandle and several cloud lines were observed near the dryline, the dryline itself did not initiate any storms over the intensive observation region (IOR). Possible reasons for this lack of convection are discussed. Strong capping inversion and moisture detrainment between the lifting condensation level and the level of free convection related to an overriding drier air, together with the relatively small near-surface moisture values (less than 10 g kg(sup -1)), were detrimental to CI in this case.

Demoz, Belay↗
NASA NTRS1977

Detection and interpretation of ocean roughness variations across the Gulf Stream inferred from radar cross section observations

Radar cross section data shows that the Gulf Stream has a higher cross section per unit area (interpreted here as a greater roughness) than the water on the continental shelf. A steep gradient in cross section was often seen at the expected location of the western boundary. There were also longer-scale (10-20 km) gradual fluctuations within the stream of significant magnitude. These roughness variations are correlated with the surface shear stress that the local wind imposes on the sea. Using the available surface-truth information concerning the wind speed and direction, an assumed Gulf Stream velocity profile, and high-resolution ocean-surface temperature data obtained by the VHRR onboard a NOAA-NESS polar-orbiting satellite, the present study demonstrates that the computed surface stress variation bears a striking resemblance to the measured radar cross-section variations.

Weissman, D. E.↗
NASA NTRS1998

Nineteenth International Laser Radar Conference

This publication contains extended abstracts of papers presented at the Nineteenth International Laser Radar Conference, held at Annapolis, Maryland, July 6-10, 1998; 260 papers were presented in both oral and poster sessions. The topics of the conference sessions were Aerosol Clouds, Multiple Scattering; Tropospheric Profiling; Stratospheric/Mesospheric Profiling; Wind Profiling; New Lidar Technology and Techniques; Lidar Applications, including Altimetry and Marine; Space and Future Lidar; and Lidar Commercialization/Eye Safety. This conference reflects the breadth of research activities being conducted in the lidar field. These abstracts address subjects from lidar-based atmospheric investigations, development of new lasers and lidar system technology, and current and future space-based lidar systems.

Upendra N. Singh↗
NASA NTRS1998

Nineteenth International Laser Radar Conference

This publication contains extended abstracts of papers presented at the Nineteenth International Laser Radar Conference, held at Annapolis, Maryland, July 6-10, 1998; 260 papers were presented in both oral and poster sessions. The topics of the conference sessions were Aerosol Clouds, Multiple Scattering; Tropospheric Profiling, Stratospheric/Mesospheric Profiling; Wind Profiling; New Lidar Technology and Techniques; Lidar Applications, Including Altimetry and Marine; Space and Future Lidar; and Lidar Commercialization/Eye Safety. This conference reflects the breadth of research activities being conducted in the lidar field. These abstracts address subjects from lidar-based atmospheric investigations, development of new lasers and lidar system technology, and current and future space-based lidar systems.

Upendra N. Singh↗
NASA NTRS1996

Wind Monitor

NASA needed a way to make high-resolution measurements of the wind profile before launching Saturn vehicles. The standard smooth-surface weather balloons zigzagged or spiraled as they ascended due to air vortices that shed off the surface at various positions, which made accurate radar-tracking measurement impossible. A Marshall Space Flight Center engineer modified the surface of the balloons with conical dixie cups, which stabilized them. Now produced by Orbital Sciences Corporation, the Jimsphere is the standard device at all U.S. missile/launch vehicle ranges.

Source record↗
NASA NTRS1994

The discrepancy between stratospheric ozone profiles from balloon soundings and from other techniques: A possible explanation

Regular balloon ozone soundings with electrochemical sondes have been performed at Uccle since 1969. More than 450 ozone soundings between 1985 and 1989 were used to calculate the altitudes Zs from the VIZ radiosonde data and the altitudes Zr deduced from the tracking of the balloon train with a primary wind-finding radar. The values of Zs at fixed times appeared to be systematically too low as compared to Zr. The differences Zr-Zs increase with altitude; at 30 km the annual mean values of Zr-Zs (plus or minus standard deviation) vary between 590 plus or minus 910 m and 1410 plus or minus 1160 m, according to the pressure calibration of different manufacturing series of radiosondes. From these results it is found that around the 30 km level the ozone concentrations calculated from soundings with VIZ sondes are too low by 7.5 to 14 percent, depending upon the manufacturing series of radiosondes. At least part of the discrepancy which has often been found between ozone profiles from balloon soundings and from other techniques such as rocket observations or Umkehr measurements may be explained by this effect. An altitude correction would have important consequences as to the climatology of ozone in the middle stratosphere as adopted at the moment. About half of the day-to-day variability of ozone observed from soundings with VIZ radiosondes above the 30 km level, is induced by the variability of Zr-Zs. The agreement between altitudes calculated from radar data and Vaisala radiosondes is much better; from 34 comparative soundings a mean difference (plus or minus standard deviation) of about -300 plus/minus 180 m was found at 30 km.

Demuer, Dirk↗
NASA NTRS1977

An investigation of the temporal character of mesoscale perturbations in the troposphere and stratosphere

The effectiveness of mesoscale models in explaining perturbations observed in vertical detailed wind profile measurements in the troposphere and lower stratosphere is assessed. The structure and persistence of the data were analyzed and interpreted in terms of several physical models with the goal of establishing explanations for the observed persistent features of the mesoscale flow patterns. The experimental data used in the investigation were obtained by a unique detailed wind profile measurement system. This system is capable of providing resolution of 50 to 100 m wavelengths for the altitude region from approximately 200 m to 18 km. The system consists of a high-resolution tracking radar and special super-pressure balloon configuration known as a Jimsphere.

Vaughan, W. W.↗
NASA NTRS2014

Offshore Wind Measurements Using Doppler Aerosol Wind Lidar (DAWN) at NASA Langley Research Center

The latest flight demonstration of Doppler Aerosol Wind Lidar (DAWN) at NASA Langley Research Center (LaRC) is presented. The goal of the campaign was to demonstrate the improvement of DAWN system since the previous flight campaign in 2012 and the capabilities of DAWN and the latest airborne wind profiling algorithm APOLO (Airborne Wind Profiling Algorithm for Doppler Wind Lidar) developed at LaRC. The comparisons of APOLO and another algorithm are discussed utilizing two and five line-of-sights (LOSs), respectively. Wind parameters from DAWN were compared with ground-based radar measurements for validation purposes. The campaign period was June - July in 2013 and the flight altitude was 8 km in inland toward Charlotte, NC, and offshores in Virginia Beach, VA and Ocean City, MD. The DAWN system was integrated into a UC12B with two operators onboard during the campaign.

Beyon, Jeffrey Y.↗
NASA NTRS2015

Validation of Rain Rate Retrievals for the Airborne Hurricane Imaging Radiometer (HIRAD)

NASA's Global Hawk aircraft (AV1)has two microwave sensors: the passive Hurricane Imaging Radiometer (HIRAD), and the active High-altitude Imaging Wind and Rain Airborne Profiler(HIWRAP). Results are presented for a rain measurement validation opportunity that occurred in 2013, when the AV1 flew over a tropical squall-line that was simultaneously observed by the Tampa NEXRAD radar. During this experiment, Global Hawk made 3 passes over the rapidly propagating thunderstorm, while the TAMPA NEXRAD performed volume scans every 5 minutes. In this poster, the three-way inter-comparison of HIRAD Tb (base temperature), HIWRAP dbZ (decibels relative to equivalent reflectivity) and NEXRAD rain rate imagery are presented. Also, observed HIRAD Tbs are compared with theoretical radiative transfer model results using HIWRAP Rain Rates.

Retrieval↗