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Remote Sensing Facility (RSF)

• Development and field operation of remote sensing facilities, including Doppler weather radar and lidar systems, and passive remote sensors.
• Consulting with users of RSF facilities on field project design, field project operations, data analysis, and data interpretation.
• Development and operation of display systems and software for editing, display, and analysis of field data.
• Conduct of scientific research and development closely related to the ATD and RSF missions.
• Collaboration with scientists and engineers in universities, other research organizations, and NCAR divisions in developing new facilities and data analysis techniques.

RSF operated the S-Pol radar in support of the PRECIP-98 studies in the Melbourne, Florida area, aimed at improving radar precipitation measurement techniques. At that same site, the system was also used to support NEXRAD radar technique development and NASA/TRMM research activities.

The ELDORA airborne Doppler radar system was deployed to the U.S. Great Lakes region in support of the Lake-ICE and Snowband field programs in that area. These studies jointly addressed lake-induced convection and the formation of large snowbands by extratropical cyclones in the Midwestern U.S.

The SABL lidar system was operated by RSF staff on the Electra in support of Lake ICE/Snowband, and then in both ground and shipboard configurations for the pre-INDOEX experiment, which was based in the Maldives Islands.

AIMR was upgraded and operated on the NCAR C-130 aircraft in support of the SHEBA study of sea ice in the Arctic Ocean, and then in the WiFE Test study of wildfire behavior.

RSF development activities included upgrades to S-Pol that improved data quality in preparation for PRECIP-98, upgrades to AIMR for SHEBA and WiFE, development of a significantly improved optical laboratory, and design for a side-scanning configuration of SABL in an under-wing pod on the NSF/NCAR C-130 aircraft. The activities of the RSF Optical Remote Sensing Program, a joint program with the NOAA Environmental Technology Laboratory (ETL), included refurbishment of the High Resolution Doppler Lidar (HRDL), a 2-µm Doppler lidar, and continued USWRP-supported development of a water-vapor DIAL profiling system intended for future use as a part of ISS.

Remote Sensors and Capabilities

Electra Doppler Radar (ELDORA). The ELDORA radar is a dual-beam X-band Doppler radar mounted on the NSF/NCAR Electra aircraft. The fore and aft radar beams spin about the longitudinal axis of the aircraft, providing dual-Doppler measurements of internal storm structure and motions as the aircraft flies past the storm. The vector wind field can be measured at scales down to about 300 meters, and, with lower resolution, out to ranges of 60 km. Through use of a complex transmitted waveform, an unambiguous velocity range of up to ± 100 m/s can be obtained.

Weather Avoidance Radar Data System (WARDS). The WARDS was upgraded and fielded during the year to provide radar reflectivity maps along the aircraft flight path during the Lake-ICE/Snowband project. The improved instrument now plots reflectivity data on an aircraft track display in fixed-earth coordinates. This capability greatly enhances the ability of the principal investigator to direct Electra flights by showing the weather echoes within 50 to 200 km of the aircraft in all directions. This display is now available to users at the scientific workstations on the Electra and C-130 aircraft.

Doppler on Wheels (DOW). During FY 1998, RSF continued its collaboration with Josh Wurman of the University of Oklahoma on various signal processing, antenna-control, and other technical improvements to the DOW radars. Operated by Wurman and a University of Oklahoma crew, the DOW radars supported convective storm, tornadoes, and hurricane landfall research during FY 1998.

Airborne Imaging Microwave Radiometer (AIMR). The Airborne Imaging Microwave Radiometer is a dual-frequency (37 and 90 GHz), dual-polarization, scanning radiometer. It was originally constructed for Atmospheric Environment Service (AES/CARD) in Canada for remote airborne measurements of surface ice. On indefinite loan to NCAR, AIMR received a major refurbishment led by RSF engineer Craig Walther in preparation for the FY 1998 SHEBA and WiFE Test experiments. The improved AIMR has improved calibration and characterization of the radio frequency circuitry, improved temperature control, revamped antenna control, and a newly installed onboard data system with modern data processing, display, and recording capabilities.

Optical Remote Sensors: The RSF optical remote sensing activities include SABL, and several joint projects with NOAA/ETL on lidar development (see RSF Sensor Development). SABL is designed to measure and map distributions of relative aerosol concentrations. It is a dual-wavelength system operating at 532 and 1064 nm and transmitting up to 60 pulses per second. Each pulse has approximately 75 mJ of 1064 nm energy and 45 mJ of 532 nm energy. A 14-inch-diameter Cassegrain telescope receives the transmitted energy scattered back to the receiver by aerosols in the atmosphere. The received signal can be resolved down to 3.75 m in range. A real-time data display allows scientists to use SABL for real-time experimental control during field studies. SABL can be operated on the ground, on board ship, or on the Electra or C-130. Another system, the Ozone Differential Absorption Lidar (O₃ DIAL), jointly operated with NOAA/ETL since FY 1996, was available but not used during FY 1998.

Data Management: The RSF data management capabilities are an integral portion of the RSF remote sensing instruments, providing routine data archival, calibration, and data access capabilities for the users of RSF instruments. The growing number of RSF-supported instruments, and large number of field projects in FY 1998, together with worldwide fielding, presented a challenge that has required improved staff efficiency and additional computer hardware during the year.

Field Support Activities

Lake-effect Initiation of Convection Experiment (Lake-ICE). George Young (Pennsylvania State University) used ELDORA to study lake-induced boundary-layer convective phenomena on the meso- and microscales and the impact of these phenomena on regional atmospheric circulations. Data were collected on lake-induced convection episodes of different intensities during eight research missions. ELDORA was used at maximum sensitivity to examine the coherent structures within the boundary layer. Some high-level legs were flown to obtain SABL measurements of boundary-layer depth.

Snow Band Dynamics Experiment (Snowband). Robert Rauber (University of Illinois) used ELDORA to measure the dynamic and thermodynamic structure of heavy precipitation bands that form in the northwest quadrant of continental cyclones and in "reverse lake-effect" regions west of Lake Michigan. Three research flights provided excellent ELDORA measurements of details of the three-dimensional airflow within the snowbands.

PRECIP-98/Tropical Experiment (PRECIP-98). This program using the S-Pol radar is one in a series of experiments being conducted in different geographic and climatic regions to improve radar estimation of rainfall. The radar was used by Edward Brandes (RAP) in an area south of Melbourne, Florida. This project coincided with the Melbourne Ground Validation field campaign for NASA’s Tropical Rainfall Measuring Mission (TRMM), utilizing rain-gauge data in south-central Florida. A comprehensive study of the usefulness of polarimetric radar in estimating precipitation provided a basis for determining the cost effectiveness of adding dual polarization to the WSR-88D. A large quantity of data with high spatial and temporal resolution were obtained in regions optimal for comparison with data from the Melbourne WSR-88D (NEXRAD) radar and with observations from dense rain-gauge networks. Preliminary analyses suggest that the current WSR-88D rainfall algorithm significantly underestimates the amount of rainfall, and that addition of capabilities similar to those of S-Pol will significantly improve the precipitation measurement capabilities of NEXRAD. Ongoing research will determine the optimal combination of parameters to achieve estimates more consistent with the rain gauges.

Surface Heat Budget of the Arctic Ocean (SHEBA). Judith Curry (University of Colorado) used the newly refurbished AIMR in this experiment to determine the characteristics and evolution of Arctic surface sea ice. AIMR was flown on the C-130 aircraft based out of Fairbanks, Alaska during two research periods in May and July 1998. Missions were flown to the north over the Arctic Ocean, where the SHEBA ship was frozen in the ice-pack during the winter. AIMR measurements mapped the age of the ice in the area surrounding the ship and the leads in the ice, determining when those leads had frozen over, and measuring the percentage of open water. The data from SHEBA will also be used to develop algorithms for measuring column-integrated liquid water and water vapor beneath the aircraft. These algorithms will be used with AIMR during the INDOEX experiment.

Wildfire Experiment (WiFE Test). During summer 1998, Larry Radke (ATD) and Terry Clark (MMM) used the AIMR on the C-130 to observe the dynamics and thermodynamics of intense forest fires. These data will be used with the Clark convection model to refine the model’s ability to predict the structure and evolution of forest fires. Results from WiFE suggest that comparison of the horizontal and vertical polarization channels of AIMR at 37 GHz can estimate the amount of fuel available for burning in the fire. The Clark model is one of the few simulations today that takes into account the amount and location of fuel available to the fire in predicting the fire track and behavior. Since AIMR has never been used as a vegetation (fuel) measurement device before, the sensor was flown over two different experimental forests for ground-truth verification of the vegetation algorithm. The AIMR data also aided in mapping the fuel in the path of the fires and in mapping the extent of the fire. Preliminary results show that AIMR is effective at seeing through the smoke and measuring the actual fire. Processing and studying this data set has just begun.

Pre-Indian Ocean Experiment (Pre-INDOEX). SABL was used by Andrew Heymsfield (MMM) in support of the pre-INDOEX experiment. After being operated on the ground in Male, Maldives for 10 days, the system was installed on the Indian ship R/V Sagar Kanya and measurements were taken during a cruise in the Indian Ocean. In addition to operating SABL, RSF staff also launched two balloon soundings per day and operated a vertically staring radiometer used to measure column-integrated liquid water and water vapor. Much of the interest in the INDOEX experiment lies in determining how the aerosol cloud coming off the Indian sub-continent is dispersed over the Indian Ocean. The SABL data were intended to map this plume, believed sometimes to be trapped in the tropopause. The Sagar Kanya sailed from Male to Mauritius and then back to Goa, India, with SABL operating continuously, 24 hours per day. This provided two separate transects of the ICTZ, as well as two fairly complete north-south and east-west transects of the eastern Indian Ocean. Data collected from all three instruments has been studied extensively by Heymsfield and has been used in planning the main INDOEX experiment, scheduled for mid-FY 1999.

NEXRAD Time Series Data Collection. RSF has been developing techniques for improving data quality of the WSR-88D radars in the NEXRAD system. These techniques are equally applicable to S-Pol and other ATD sensor systems, and the technology will be installed in these systems at an appropriate future time. Dual-PRT data were collected at S-Pol during the PRECIP-98 program and will be analyzed to compare the actual performance with the theoretical expectation in a formal statistical test and evaluation.

Sensor Development Activities

S-Band Doppler Dual-Polarimetric Radar (S-Pol). In preparation for PRECIP-98, the S-Pol radar was upgraded in several respects. The RSF VIRAC signal processor on S-Pol was upgraded to enable the time series data collection needed for support of NOAA/OSF NEXRAD time series tests, and the antenna pattern was carefully evaluated. Data from these experiments are now being analyzed, and refinements to the radar and its software to improve future data quality are being planned. The processor was also upgraded for recording the full co- and cross-polarization matrix. Data quality has been improved considerably. Antenna patterns, solar calibrations, and sphere measurements were performed to improve data calibration. The receivers were modified to improve differential reflectivity stability for more accurate rainfall measurements. The radar control center was completed. Real-time polarization rainfall and microphysics product displays are now available in the field. The S-Pol radar is now fully packaged and operational.

Polarimetric Hydrometeor Rainfall Particle Identification. J. Vivekanandan, Ed Brandes, Scott Ellis, Dick Oye, and Jim Wilson developed a precipitation particle-typing product that ran in real-time during PRECIP-98. This product applies fuzzy-logic techniques to the S-Pol polarimetric variables to estimate hydrometeor particle type. This successful new development is the first time these capabilities have been available at a precipitation radar in real-time.

Solid-State High-Resolution Doppler Lidar (HRDL). Following the Lidars in Flat Terrain (LIFT) program in mid-FY 1997, the joint NCAR-NOAA/ETL Optical Remote Sensing Program performed a major upgrade on HRDL. The upgrade includes a new pump system, improved stability and Doppler coherence, and improved packaging. HRDL will be ready for a field-test program planned for summer 1998. Volker Wulfmeyer also investigated the requirements for water-vapor DIAL system on ground-based and airborne platforms for accurate water-vapor and turbulence measurements. These results will be applied to the needs of future experimental programs. Wulfmeyer studied the performance of direct-detection water-vapor DIAL in comparison to heterodyne water-vapor DIAL using the Mini-MOPA system (NOAA) and the 2-µm Doppler HRDL lidar (NCAR-NOAA). The latter could allow simultaneous water-vapor and wind measurements with a single lidar system.

DIAL Water-Vapor Profiling Lidar. During FY 1998, system design and initial test and development of system concepts were initiated on this new, relatively inexpensive, USWRP-supported lidar system for the remote profiling of water vapor. When completed, the system will be an important addition to ATD's ISS profiling capabilities. Initial laboratory testing of the system is planned for early FY 1999.

NEXRAD Support. RSF has an ongoing, NOAA-funded technique development effort aimed at improving the data quality of the nation's NEXRAD (WSR-88D) radars. These techniques include development of anomalous propagation (AP) clutter mitigation, automatic range-velocity folding mitigation, installation of the RAF-developed A-1 Data Recorder on the OSF NEXRAD radar, and polarization radar hydrometeor identification techniques, also applicable to S-Pol and other ATD sensor systems. This arrangement is a unique coupling of the research and operational communities for their common benefit.

Jeff Keeler and Cathy Kessinger (RAP) continued the AP Clutter Mitigation development based on fuzzy logic; this improvement is planned for implementation on NEXRAD and S-Pol in FY 2000. A parallel, ongoing WSR-88D instrumentation support effort monitors the operating and environmental conditions of that radar. Many of the concepts developed as a part of the NEXRAD support effort may be applied to S-Pol and ELDORA in the future. An RSF-designed data acquisition system has been used on both the WSR-88D and S-Pol for assessing data quality and defining needed system upgrades.

Chuck Frush continued the Range/Velocity Folding Mitigation technique development for application to NEXRAD and S-Pol. In collaboration with NOAA's National Severe Storms Laboratory (NSSL), CSU, and the University of Colorado, this work involves theoretical studies, test-data acquisition, and performance testing of advanced pulsing waveforms (phase-coded and dual-PRT) to improve both research radar data quality and the acceptability of operational weather products from the WSR-88D. This work is being tested on the S-Pol radar during field projects in FY 1998 and FY 1999, and is targeted for implementation on NEXRAD in several years.

The NEXRAD Archive 1 Recorder and A-1 Data Analysis Tool, developed by RSF engineers Don Ferraro and Joe VanAndel, was installed on the OSF NEXRAD radar during this reporting period. Installation of this RSF-developed data recording and analysis tool, and training of OSF staff to use it, have fundamentally improved the ability of OSF staff to investigate aspects of NEXRAD operation and to improve the radar's capabilities. The NEXRAD radars frequently experience anomalous propagation conditions, which produce confusing radar-product displays and erroneous hydrology estimates. By analyzing these data using alternative signal-processing techniques, RSF staff are verifying new algorithms that mitigate the anomalous propagation problem. When completed, these algorithms will be implemented on the NEXRAD radar network, and, as appropriate, on S-Pol.

Research Activities

Mesoscale Alpine Program (MAP). Peter Hildebrand and Jim Wilson are assisting with planning of U.S. participation MAP, an international study of the effects of complex topography on wind, precipitation, and flooding. The orographic precipitation portion of MAP seeks to better understand the factors that result in severe mountain-influenced flooding events, the structure of the storms that produce severe flooding events, and the precursors that can be used to improve prediction and warning of those events. The program will include extensive use of numerical prediction models and ground measurement networks. RSF scientists will be associated with the radar and aircraft field programs for the MAP intensive observation period in autumn 1999, and in the subsequent evaluation of the data on strong precipitation events that are observed during MAP.

Hydrometeor Particle Type Identification. This capability has been extended during FY 1998 by Jim Wilson, J. Vivekanandan, Ed Brandes (RAP), Scott Ellis, and Dick Oye, and incorporated into the S-Pol radar precipitation product package to display hydrometeor estimates in real time. The lack of in-situ microphysical data has been a limiting factor in verifying the accuracy of this particle classification method. During FY 1998 the technique was improved and verification measurements were obtained with cloud physics aircraft during PRECIP-98 and the Florida component of TRMM/TExas and Florida UNderflights (TEFLUN-B). Studies are underway to determine whether the particle classification technique can also distinguish convective from stratiform regions in clouds. The separation of cloud systems into convective and stratiform is one of the primary objectives of TRMM for obtaining four-dimensional structures of latent heating in the atmosphere.

Hurricane Research. Scientists at RSF and NOAA's Hurricane Research Division (HRD) in Miami are collaborating in investigating hurricane eyewall and rainband structures, the relationship of these structures to hurricane intensification, and the Ground Based VTD hurricane intensity and track algorithm. Wen-Chau Lee and NOAA researchers are jointly developing the operational Ground-Based Velocity Track Display (GBVTD) algorithm for use in forecasting hurricane track and intensity using NEXRAD radars. The first real-time, GBVTD-derived, low-level tropical cyclone primary circulation was successfully performed for Hurricane Earl (1998). The National Hurricane Center is assessing the usefulness of the technique for estimating parameters of landfalling tropical cyclones, such as mean tangential wind and radius of hurricane-force winds. Other hurricane research by Peter Hildebrand, Robert Gall (MMM), and Kevin Petty (ASP) is focused on circulation structure within the hurricane eye, the relationship of changes in hurricane eye airflow to the formation of new hurricane eyewalls and to hurricane re-intensification, and the effect of hurricane rainband structures on overall hurricane dynamics. This study also involves examination of the evolution of the eyewall and rainband convection in terms of shearing instability and surface friction.

Severe Storm Research. Using the high-resolution ELDORA data collected during VORTEX (1995), Wen-Chau Lee has examined fine structures within a squall line such as mesocyclones, Kelvin-Helmholtz instabilities near inflow/outflow boundaries, vaults, and gravity waves near storm tops. With the exception of mesocyclones, these features have not been studied in detail in the past. Dual-Doppler radar analyses, satellite images, damage surveys, and profiler data will be used to investigate these features. This research is collaborative among scientists from RSF, UCLA, and HRD. In a related study, Lee worked with John Gamache (NOAA/HRD) to develop and test a variational dual-Doppler wind-analysis technique to fully utilize airborne Doppler radar data at high incidence angles. Such data cannot be handled by conventional dual-Doppler methods.

Maritime Continent Thunderstorm Experiment (MCTEX). Jim Wilson, in collaboration with Tom Keenan of the Australian Bureau of Meteorology (BoM) and Rit Carbone of MMM, continued his research on the initiation and evolution of thunderstorms in northern Australia as part of MCTEX. These large thunderstorms, called Hector, are among the highest in the world and result from convection forced by local sea breezes. These storms form at locations controlled by the low-level environmental flow, e.g., where a gust front from small showers and thunderstorms interacts with the sea-breeze front.

Fronts and Atlantic Storms Experiment (FASTEX). During FY 1998, Peter Hildebrand’s extra-tropical cyclone research was directed at obtaining an improved understanding of the structure and dynamics of oceanic, winter cold fronts as observed in the recent FASTEX field program. Many of the oceanic cold fronts observed in FASTEX, and in other recent field efforts, have a character similar to density currents, being extremely shallow and having very large horizontal scales. Using FASTEX data from research aircraft, research vessels, satellites and sounding systems, Hildebrand is investigating the role of frontal rainbands in developing and maintaining these shallow frontal structures, and the relationship of these structures to the larger scale weather pattern.

Boundary-Layer Research. RSF scientists Volker Wulfmeyer and Tammy Weckwerth continued their analyses of Flatland/LIFT data. They have compared the different scales of motion observed by the DOW-1 radar and the HRDL lidar. They continue to collaborate with scientists from the South Dakota School of Mines and Technology and the Illinois State Water Survey in this work, with the goal of determining the causes of boundary-layer coherent structures.

Water-Vapor Measurements. Volker Wulfmeyer has used available data from different DIAL systems to estimate the performance of potential future water-vapor DIAL systems for measurements in the troposphere, such as an advanced water-vapor DIAL on the HIAPER aircraft. Initial simulations show that a high average-power DIAL system could have a range as long as 20 km with temporal and spatial resolutions of 10s and a few hundred meters, respectively. RSF staff have also initiated interactions with international researchers to measure atmospheric water vapor. Preliminary studies with scientists from Delft University in Holland using high-resolution interferometric synthetic-aperture radar (SAR) techniques onboard satellites are enlightening. With some assumptions, information about the water-vapor content of the troposphere can be derived.
 
 

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