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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 NTRS2011

Sensitivity of Spaceborne and Ground Radar Comparison Results to Data Analysis Methods and Constraints

With the availability of active weather radar observations from space from the Precipitation Radar (PR) on board the Tropical Rainfall Measuring Mission (TR.MM) satellite, numerous studies have been performed comparing PR reflectivity and derived rain rates to similar observations from ground-based weather radars (GR). These studies have used a variety of algorithms to compute matching PR and GR volumes for comparison. Most studies have used a fixed 3-dimensional Cartesian grid centered on the ground radar, onto which the PR and GR data are interpolated using a proprietary approach and/or commonly available GR analysis software (e.g., SPRINT, REORDER). Other studies have focused on the intersection of the PR and GR viewing geometries either explicitly or using a hybrid of the fixed grid and PR/GR common fields of view. For the Dual-Frequency Precipitation Radar (DPR) of the upcoming Global Precipitation Measurement (GPM) mission, a prototype DPR/GR comparison algorithm based on similar TRMM PR data has been developed that defines the common volumes in terms of the geometric intersection of PR and GR rays, where smoothing of the PR and GR data are minimized and no interpolation is performed. The PR and GR volume-averaged reflectivity values of each sample volume are accompanied by descriptive metadata, for attributes including the variability and maximum of the reflectivity within the sample volume, and the fraction of range gates in the sample average having reflectivity values above an adjustable detection threshold (typically taken to be 18 dBZ for the PR). Sample volumes are further characterized by rain type (Stratiform or Convective), proximity to the melting layer, underlying surface (land/water/mixed), and the time difference between the PR and GR observations. The mean reflectivity differences between the PR and GR can differ between data sets produced by the different analysis methods; and for the GPM prototype, by the type of constraints and categorization applied to the data. In this paper, we will show results comparing the 3-D gridded analysis "black box" approach to the GPM prototype volume-matching approach, using matching TRMM PR and WSR-88D ground radar data. The affects of applying data constraints and data categorizations on the volume-matched data to the results will be shown, and explanations of the differences in terms of data and analysis algorithm characteristics will be presented. Implications of the differences to the determination of PR/DPR calibration differences and use of ground radar data to evaluate the PR and DPR attenuation correction algorithms will be discussed.

Morris, Kenneth R.↗
NASA NTRS1980

Radar observations of wave transformations in the vicinity of islands

Remote sensing by ground-based HF radar and airborne synthetic aperture radar and in situ wave measurements performed on March 25, 1977 during the West Coast Experiment have made it possible to form an overall picture of the 7-sec-period wave climate over a 35,000 sq km region off the southern California coast. The picture which emerges from these measurements shows a broad deep-ocean directional distribution arriving from the west and being significantly modified as it travels coastward passing San Clemente and Santa Catalina islands.

Vesecky, J. F.↗
NASA NTRS1972

Fine structure of the lower atmosphere as seen by high resolution radar

A ground-based vertically pointing FM-CW radar is described that permits remote probing of the refractive index structure in the troposphere. The radar has the characteristics of extremely high sensitivity, ultrahigh range resolution, and close minimum detection range without clutter. The sounder routinely detects layer structures in the lower troposphere. These layers are always associated with gradients in the vertical refractive index profile, and are frequently very thin, approaching the resolution of the radar (1 m). Very often they are perturbed by wave motions. Examples of various wave patterns are presented, and an explanation is given for organized substructures frequently superimposed on larger scale wave motions.

Richter, J. H.↗
NASA NTRS1991

CLASS: Coherent Lidar Airborne Shear Sensor. Windshear avoidance

The coherent lidar airborne shear sensor (CLASS) is an airborne CO2 lidar system being designed and developed by Lockheed Missiles and Space Company, Inc. (LMSC) under contract to NASA Langley Research Center. The goal of this program is to develop a system with a 2- to 4-kilometer range that will provide a warning time of 20 to 40 seconds, so that the pilot can avoid the hazards of low-altitude wind shear under all weather conditions. It is a predictive system which will warn the pilot about a hazard that the aircraft will experience at some later time. The ability of the system to provide predictive warnings of clear air turbulence will also be evaluated. A one-year flight evaluation program will measure the line-of-sight wind velocity from a wide variety of wind fields obtained by an airborne radar, an accelerometer-based reactive wind-sensing system, and a ground-based Doppler radar. The success of the airborne lidar system will be determined by its correlation with the windfield as indicated by the onboard reactive system, which indicates the winds actually experienced by the NASA Boeing 737 aircraft.

Targ, Russell↗
NASA NTRS1994

Studies of microwave scattering and canopy architecture for boreal forests

Our primary objectives during the last year have been to develop a helicopter-borne radar system for measuring microwave backscatter from vegetation and to use this system to study the characteristics of backscatter from the boreal forest. Our research is aimed at refining the current microwave models and using these improvements for more accurate interpretation of SAR data. SAR data are very useful for monitoring the boreal forest region because of the microwave signal's ability to penetrate clouds and to see at night. Meeting these objectives involves several stages of development. The first stage is the design and implementation of a frequency-modulated continuous-wave (FM-CW) radar system with the capability of measuring backscatter at three frequencies and four polarizations at each frequency. These requirements necessitate a twelve-channel radar system. Using three frequencies is advantageous because it allows us to look at different parts of the canopy. For instance, the lower frequency signal penetrates deeper into the canopy and allows us to see the ground while the high frequency signal is scattered more by the leaves and needles and typically does not penetrate to the floor of the forest. We designed the radar starting with the antenna system. We then developed the intermediate frequency (IF) and radio frequency (RF) sections of the radar. Also, the need to collect data from twelve channels during each flight line presented a complex data acquisition problem that we solved by using a high-speed data acquisition board. After construction, the radar was tested at the lab. We performed extensive testing of the IF and RF systems of the radar during this time. Once we were satisfied with the operation of the radar it was shipped to Canada for use in the second intensive field campaign (IFC-2) from July 16 - August 8, 1994. During IFC-2, we collected backscatter data over the experimental sites in the southern study area (SSA). Additionally, we used a ground-based step-frequency radar to measure the reflection coefficient of the forest floor at the old jack pine (OJP) and young jack pine (YJP) sites. The ground-based radar data have been processed and a frew examples are included in this report. we are currently processing the helicopter-borne radar data.

Lockhart, G. Lance↗
NASA NTRS1977

HF excited instabilities in space plasmas

It has now become technologically feasible to construct ground-based HF radar systems which can deliver RF energy to the ionospheric plasma, with power densities sufficient to alter the ionospheric electron thermal budget and plasma characteristics. Effects produced by a ground-based transmitter of a power aperture of the order of 10,000 Mw sq m in the frequency range from 4 to 12 MHz are shown in a graph. Another graph presents a profile of electron gas temperature enhancement due to energy deposition by a high power HF transmitter. The conduction of high-power HF ionospheric plasma experiments is discussed. Attention is given to plasma instabilities, wave-particle acceleration effects, spacial and time scales, parametric instabilities, spread-F, and the possibility of placing high power-aperture radars on an orbiting space platform.

Carlson, H. C., Jr.↗
NASA NTRS2010

Plans for the Meter Class Autonomous Telescope and Potential Coordinated Measurements with Kwajalein Radars

The National Aeronautics and Space Administration's (NASA) Orbital Debris Program Office is teaming with the US Air Force Research Laboratory's (AFRL) Maui Optical Site to deploy a moderate field-of-view, 1.3 m aperture, optical telescope for orbital debris applications. The telescope will be located on the island of Legan in the Kwajalein Atoll and is scheduled for completion in the Spring of 2011. The telescope is intended to sample both low inclination/high eccentricity orbits and near geosynchronous orbits. The telescope will have a 1 deg diagonal field-of-view on a 4K x 4K CCD. The telescope is expected to be able to detect 10-cm diameter debris at geosynchronous altitudes (5 sec exposure assuming a spherical specular phase function w/ albedo =0.13). Once operational, the telescope has the potential of conducting simultaneous observations with radars operated by the US Army at Kwajalein Atoll (USAKA) and located on the island of Roi-Namur, approximately 55 km to the north of Legan. Four radars, representing 6 frequency bands, are available for use: ALTAIR (ARPA-Long Range Tracking and Instrumentation Radar) operating at VHF & UHF, TRADEX (Target Resolution and Discrimination Experiment) operating at L-band and S-band, ALCOR (ARPA-Lincoln C-band Observables Radar) operating at S-band, and MMW (Millimeter Wave) Radar operating at Ka-band. Also potentially available is the X-band GBRP (Ground Based Radar-Prototype located 25 km to the southeast of Legan on the main island of Kwajalein.

Stansberry, Gene↗
NASA NTRS1978

Application of microprocessors to spacecraft synthetic aperture radar processing

A ground-based digital synthetic aperture radar (SAR) processor capable of correlating images from raw spacecraft data at real-time rates is currently under development. The processor design requirements are particularly formidable due to (1) range migration effects resulting from planetary curvature and rotation, (2) antenna beam pointing errors, and (3) variation of the Doppler reference function with changing orbital parameters. Based upon the current effort, this paper describes a candidate real-time on-board SAR processing implementation approach that might evolve for future spacecraft applications. Key features include the use of custom large scale integration (LSI) charge-coupled device (CCD) technology to accomplish the correlation functions and microprocessor technology to effect control.

Arens, W. E.↗
NASA NTRS1984

Analysis of lidar, radar and satellite measurements on severe thunderstorms and their environments

Intercomparison of wind data from the airborne Doppler lidar, ground-based Doppler radars, the 444 m NSSL-KTVY tower, and rawinsonde were completed. The vertical profile of wind in the PBL measured by the radars compared favorably with the profiles measured by the tower and rawinsonde while the one obtained from lidar data differed from the other three by as much as 3m/sec in wind speed and 38 degrees in direction. The time dependence of differences in wind estimates from radar and lidar suggested that these discrepencies could be attributed to a Schuler resonance in the aircraft's inertial navigation system which caused an erroneous component of the aircraft's velocity vector to be subtracted from the lidar radial velocities, thus creating errors in the synthesized wind speed and direction. The vertical profile of turbulent fluctuations of the horizontal wind detected by the different systems compared well. Also, spectra from the different sensing systems compared well in both magnitude and shape, suggesting that the lidar and radar detected similar turbulent structure.

Bluestein, H.↗
NASA NTRS1999

Radar Observations of Convective Systems from a High-Altitude Aircraft

Reflectivity data collected by the precipitation radar on board the tropical Rainfall Measuring Mission (TRMM) satellite, orbiting at 350 km altitude, are compared to reflectivity data collected nearly simultaneously by a doppler radar aboard the NASA ER-2 flying at 19-20 km altitude, i.e. above even the deepest convection. The TRMM precipitation radar is a scanning device with a ground swath width of 215 km, and has a resolution of about a4.4 km in the horizontal and 250 m in the vertical (125 m in the core swath 48 km wide). The TRMM radar has a wavelength of 217 cm (13.8 GHz) and the Nadir mirror echo below the surface is used to correct reflectivity for loss by attenuation. The ER-2 Doppler radar (EDOP) has two antennas, one pointing to the nadir, 34 degrees forward. The forward pointing beam receives both the normal and the cross-polarized echos, so the linear polarization ratio field can be monitored. EDOP has a wavelength of 3.12 cm (9.6 GHz), a vertical resolution of 37.5 m and a horizontal along-track resolution of about 100 m. The 2-D along track airflow field can be synthesized from the radial velocities of both beams, if a reflectivity-based hydrometer fall speed relation can be assumed. It is primarily the superb vertical resolution that distinguishes EDOP from other ground-based or airborne radars. Two experiments were conducted during 1998 into validate TRMM reflectivity data over convection and convectively-generated stratiform precipitation regions. The Teflun-A (TEXAS-Florida Underflight) experiment, was conducted in April and May and focused on mesoscale convective systems mainly in southeast Texas. TEFLUN-B was conducted in August-September in central Florida, in coordination with CAMEX-3 (Convection and Moisture Experiment). The latter was focused on hurricanes, especially during landfall, whereas TEFLUN-B concentrated on central; Florida convection, which is largely driven and organized by surface heating and ensuing sea breeze circulations. Both TEFLUN-A and B were amply supported by surface data, in particular a dense raingauge network, a polarization radar, wind profilers, a mobile radiosonde system, a cloud physics aircraft penetrating the overflown storms, and a network of 10 cm Doppler radars(WSR-88D). This presentation will show some preliminary comparisons between TRMM, EDOP, and WSR-88D reflectivity fields in the case of an MCS, a hurricane, and less organized convection in central Florida. A validation of TRMM reflectivity is important, because TRMM's primary objective is to estimate the rainfall climatology with 35 degrees of the equator. Rainfall is estimated from the radar reflectivity, as well from TRMM's Microwave Imager, which measures at 10.7, 19.4, 21.3, 37, and 85.5 GHz over a broader swath (78 km). While the experiments lasted about three months the cumulative period of near simultaneous observations of storms by ground-based, airborne and space borne radars is only about an hour long. Therefore the comparison is case-study-based, not climatological. We will highlight fundamental differences in the typical reflectivity profiles in stratiform regions of MCS's, Florida convection and hurricanes and will explain why Z-R relationships based on ground-based radar data for convective systems over land should be different from those for hurricanes. These catastrophically intense rainfall from hurricane Georges in Hispaniola and from Mitch in Honduras highlights the importance of accurate Z-R relationships, It will be shown that a Z-R relationship that uses the entire reflectivity profile (rather than just a 1 level) works much better in a variety of cases, making an adjustment of the constants for different precipitation system categories redundant.

Heymsfield, G.↗
NASA NTRS1985

Preliminary planning for the Satellite Precipitation And Cloud Experiment (SPACE) Field Program

Preliminary planning has been performed to support NASA/Marshall Space Flight Center (MSFC) in the coordination of the field experiment to be conducted in Central Tennessee, Northern Alabama, and Mississippi during the Spring/Summer of 1986. The goal of Satellite Precipitation and Cloud Experiments (SPACE) is to investigate mesoscale cloud/precipitation systems and development of associated satellite remote sensing technology. The field program will incorporate remote sensing observations from aircraft, satellite imagery, radar observations, ground based lightning measurements, rawinsonde observations, and various surface meteorological observations. The coordination of existing and special observation networks will provide a data base for analysis of precipitation events and provide ground truth comparisons for remote sensing capabilities. Existing surface-based observational networks include National Weather Service Meso/Alpha Scale Rawinsonde, radar, and surface measurements; the Tennessee Valley Authority automated and manual precpitation recording stations; and NASA/MSFC lightning measurement stations. Special observational features to be implemented include a meso/beta scale rawinsonde network, a special surface observational network within the rawinsonde network, and the installation of a RADAP II/ICRAD data processing unit on the National Weather Service radar at Nashville, TN. Initial coordination of these observational requirements to accomplish the goals of SPACE have been performed.

Williams, S. F.↗
NASA NTRS1985

The structure of the convective atmospheric boundary layer as revealed by lidar and Doppler radars

Results on the structure of the convective atmospheric boundary layer based on the analyses of data from the instrumented NSSL-KTVY tower, airborne Doppler lidar, and ground-based Doppler radars are presented. The vertically averaged wind over the boundary layer was found to be insensitive to baroclinicity, supporting the hypothesis of Arya and Wyngaard (1975). The computed momentum flux profiles were affected by baroclinicity. Horizontal wind spectra from lidar, radar, and tower data compared well with each other both in shape and magnitude. A consistent peak found near 4 km in all the computed spectra might have been caused by horizontally symmetric cells with horizontal wavelength 4 times the boundary-layer height as shown in Kuettner (1971) for the case of weak wind shear.

Eilts, M. D.↗
NASA NTRS2003

An Automated Cloud-edge Detection Algorithm Using Cloud Physics and Radar Data

An automated cloud edge detection algorithm was developed and extensively tested. The algorithm uses in-situ cloud physics data measured by a research aircraft coupled with ground-based weather radar measurements to determine whether the aircraft is in or out of cloud. Cloud edges are determined when the in/out state changes, subject to a hysteresis constraint. The hysteresis constraint prevents isolated transient cloud puffs or data dropouts from being identified as cloud boundaries. The algorithm was verified by detailed manual examination of the data set in comparison to the results from application of the automated algorithm.

Ward, Jennifer G.↗
NASA NTRS2005

A Range Compensating Feed Motion Concept for Spaceborne Radar

Tropical cyclones can cause major loss of both life and property, so that improvements in forecasting motion, intensity, and rainfall are needed. Such forecasting requires accurate measurements of the current state of the cyclone. Ground-based Doppler radars have long been used as an effective means of monitoring severe precipitating storms. Because of the oceanic nature of tropical cyclones, remote monitoring from space is desirable. Recently, the Precipitation Radar (PR) [1] aboard the Tropical Rainfall Measuring Mission (TRMM) [2] satellite has demonstrated an unprecedented capacity for 3-D imaging of precipitating storms. Nonetheless, due to the relatively long TRMM return cycle (less than once per day) the value of PR data has primarily been limited to the understanding of climatological properties of tropical cyclones [3]. The return cycle can be substantially reduced by sensing from a geostationary platform.

reflector antennas↗
NASA NTRS2006

Radio Frequency (RF) Attenuation Measurements of the Space Shuttle Vehicle

Following the loss of Columbia, the Columbia Accident Investigation Board (CAIB) provided recommendations to be addressed prior to Return To Flight (RTF). As a part of CAIB Recommendation 3.4.1 - Ground Based Imagery, new C-band and X-band radars were added to the array of ground-based radars and cameras already in-situ at Kennedy Space Center. Because of higher power density considerations and new operating frequencies, the team of Subject Matter Experts (SMEs) assembled to investigate the technical details of introducing the new radars recommended a series of radio frequency (RF) attenuation tests be performed on the Space Shuttle vehicle to establish the attenuation of the vehicle outer mold line structure with respect to its external RF environment. Because of time and complex logistical constraints, it was decided to split the test into two separate efforts. The first of these would be accomplished with the assistance of the Air Force Research Laboratory (AFRL), performing RF attenuation measurements on the aft section of OV-103 (Discovery) while in-situ in Orbiter Processing Facility (OPF) 3, located at Kennedy Space Center. The second would be accomplished with the assistance of the National Institute of Standards and Technology (NIST) and the electromagnetic interference (EMI) laboratory out of the Naval Air Warfare Center, Patuxent River, Maryland (PAX River), performing RF attenuation measurements on OV-105 (Endeavour) in-situ inside the Space Shuttle Landing Facility (SLF) hangar, also located at Kennedy Space Center. This paper provides a summary description of these efforts and their results.

Scully, R. C.↗
NASA NTRS2021

Assessing the Impact of Light/Shallow Precipitation Retrievals from Satellite-Based Observations Using Surface Radar and Micro Rain Radar Observations

The accurate representation of precipitation across the Earth’s surface is crucial to furthering our knowledge and understanding of the Earth System and its component processes. Precipitation poses a number of challenges, particularly due to the variability of precipitation over time and space and whether it falls as snow or rain. While conventional measures of precipitation are reasonably good at the location of their measurement, their distribution across the Earth’s surface is uneven with some regions having no surface measurements. Spaceborne sensors have the capability of providing regular observations across the Earth’s surface that can provide estimates of precipitation. However, the estimation of precipitation from satellite observations is not necessarily straightforward. Visible and/or infrared techniques rely upon imprecise cloud-top to surface precipitation relationships, while the sensitivity of passive microwave techniques to different precipitation types is not consistent. Active microwave (radar) observations provide the most direct satellite measurements of precipitation but cannot provide estimates close to the surface and are generally not sufficiently sensitive to resolve light precipitation. This is particularly problematic at mid to high latitudes, where light and/or shallow precipitation dominates. This paper compares measurements made by ground-based weather radars, Micro Rain Radars and the spaceborne Dual-frequency Precipitation Radar to study both light precipitation intensity and shallow precipitation occurrence and to assess their impact on satellites retrievals of precipitation at the mid to high latitudes.

light precipitation↗
NASA NTRS2005

Dual-Band Deramp Radar Design for Ocean Current Measurements

A mission has been proposed to remotely measure ocean surface currents and surface wind velocities. It will provide the highest resolution and repeat time of these measurements to date for ocean current models with scientific and societal applications. A ground-based experimental radar unit is needed for proof of concept. The proposed experiment set up is to mount the radar on an oil rig to imitate satellite data acquisition. This summer, I completed the radar design. The design employs chirp/deramp topology with simultaneous transmit/receive channels. These two properties allow large system bandwidth, extended sample time, close range imaging, and low sampling rate. The radar operates in the Ku and Ka microwave bands, at 13.5 and 35.5 GHz, respectively, with a system bandwidth of 300 MHz. I completed the radar frequency analysis and research on potential components and antenna configurations. Subsequent work is needed to procure components, as well as to build, test, and deploy the radar.

Haynes, Mark S.↗
NASA NTRS2014

A Preliminary Analysis of Precipitation Properties and Processes during NASA GPM IFloodS

The Iowa Flood Studies (IFloodS) is a NASA Global Precipitation Measurement (GPM) ground measurement campaign, which took place in eastern Iowa from May 1 to June 15, 2013. The goals of the field campaign were to collect detailed measurements of surface precipitation using ground instruments and advanced weather radars while simultaneously collecting data from satellites passing overhead. Data collected by the radars and other ground instruments, such as disdrometers and rain gauges, will be used to characterize precipitation properties throughout the vertical column, including the precipitation type (e.g., rain, graupel, hail, aggregates, ice crystals), precipitation amounts (e.g., rain rate), and the size and shape of raindrops. The impact of physical processes, such as aggregation, melting, breakup and coalescence on the measured liquid and ice precipitation properties will be investigated. These ground observations will ultimately be used to improve rainfall estimates from satellites and in particular the algorithms that interpret raw data for the upcoming GPM mission's Core Observatory satellite, which launches in 2014. The various precipitation data collected will eventually be used as input to flood forecasting models in an effort to improve capabilities and test the utility and limitations of satellite precipitation data for flood forecasting. In this preliminary study, the focus will be on analysis of NASA NPOL (S‐band, polarimetric) radar (e.g., radar reflectivity, differential reflectivity, differential phase, correlation coefficient) and NASA 2D Video Disdrometers (2DVDs) measurements. Quality control and processing of the radar and disdrometer data sets will be outlined. In analyzing preliminary cases, particular emphasis will be placed on 1) documenting the evolution of the rain drop size distribution (DSD) as a function of column melting processes and 2) assessing the impact of range on ground‐based polarimetric radar estimates of DSD properties.

Carey, Lawrence↗