RSF field activities in FY 1997 included support with the S-Band Doppler Dual Polarimetric Radar (S-Pol), the airborne Electra Doppler Radar (ELDORA), and the Staring Aerosol Backscatter Lidar (SABL) system. Two projects were supported by S-Pol: the Polarimetric Radar Observations in Winter Storms (PROWS) project, and the Cooperative Atmosphere-Surface Exchange Study (CASES). Both projects addressed the need for improved precipitation measurements from research and operational radar systems. The ELDORA system supported the International Fronts and Atlantic Storm Track Experiment (FASTEX) in its study of extratropical cyclogenesis over the wintertime North Atlantic Ocean. The SABL lidar system was operated in a shipboard configuration in support of JAMSTEC's Tropical Ocean Climate Study (TOCS). On the development side, the RSF Optical Remote Sensing Program, a joint activity with the NOAA Environmental Technology Laboratory (ETL), conducted a strengthened development program that emphasized SABL upgrades, development of a 2-µm Doppler lidar, and development of an H2O-DIAL profiling system.
S-Band Doppler Dual Polarimetric Radar (S-Pol). Development of this advanced, highly-portable radar was completed in FY 1996; the initial fielding of the system occurred in FY 1997. The new system has significantly improved signal-processing and polarization-measurement capabilities, compared with earlier research radars. Based on an FAA Terminal Doppler Weather Radar (TDWR) system, S-Pol uses a high-quality antenna with very low sidelobes, a high-reliability transmitter, and parallel receivers for simultaneous co-polar and cross-polar responses. The innovative design packages S-Pol into six 20-ft shipping containers and eliminates the radome. Field operations in FY 1997 tested this novel radar design and demonstrated the simplified transportation and set-up of the system, including significantly lowered shipping costs. These field tests also provided an opportunity for the initial deployment of the S-Pol Bistatic Receiver System, which allows for dual-Doppler wind measurements in selected areas within 40-60 km of the radar.
Electra Doppler Radar (ELDORA). The ELDORA radar is a dual-beam, X-band Doppler radar mounted on the NCAR/NSF Electra. 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 FASTEX project. The upgraded WARDS 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.
Staring Aerosol Backscatter Lidar (SABL). The SABL lidar 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 Cassegrainian 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.
Ozone Differential Absorption Lidar (O3 DIAL). The Ozone DIAL lidar system, jointly operated with NOAA/ETL during FY 1996, was available but not used during FY 1997.
Table RSF-1. FY 1997 RSF Field Support Activities
| User (Affiliation) | Project | Location | Sensors | Research Period |
|---|---|---|---|---|
| Wakimoto (UCLA), Hildebrand (RSF), Testud (CNET) |
FASTEX | Shannon, Ireland | ELDORA, WARDS | Jan-Feb 97 |
| Rutledge (CSU), et al. | PROWS | Eastlake, CO | S-Pol | Jan-Mar 97 |
| Parsons (ATD/SSSF) | TOCS | Western Pacific | SABL | Jan-Mar 97 |
| Brandes (RAP) | CASES | Wichita, KS | S-Pol; Bistatic Receivers | Apr-Jun 97 |
| O’Bannon (NWS/OSF) | NEXRAD Anomalous Propagation Tests | Memphis, TN | Archive 1, Recorder | Jun-Jul 97 |
Fronts and Atlantic Storm Tracks Experiment (FASTEX). This international program based in Shannon, Ireland, focused on advancing the scientific understanding and prediction of the life cycles of North Atlantic extratropical cyclones and their associated cloud and precipitation systems. The NCAR ELDORA on the Electra aircraft was used by PIs Roger Wakimoto (UCLA), Peter Hildebrand (ATD/RSF), and Jacques Testud (CETP, France) in association with the NOAA P-3 tail Doppler radar and dropsondes released from the UK C-130 to map mesoscale structures of mature or deepening cyclone systems. The rapid-scanning abilities of ELDORA helped document the turbulent ascent and descent of air in shallow rain showers associated with cold and warm frontal systems. The WARDS was also flown on the Electra during FASTEX. The newly developed geostationary-CAPPI WARDS display allowed investigators to see convective bands ahead of the aircraft. This surveillance capability provided critical information to assist investigators in designing and refining flight patterns for optimal ELDORA data collection during FASTEX. A polar-orbiting satellite receiver was also installed on the Electra to receive satellite imagery before and during missions.
Polarimetric Radar Observations in Winter Storms (PROWS). This program used S-Pol to collect multiparameter radar observations and near-coincident ground-truth measurements (e.g., rain and snow amounts, particle types, etc.) in Front Range winter storms. The primary scientific objectives were to improve the estimation of precipitation rates and hydrometer types via radar and to evaluate the benefits of polarimetric measurement capability as a future NEXRAD enhancement. PIs Steven Rutledge, V.N. Bringi, and V. Chandrasekar (all from CSU) approached the problem from a microphysical point of view to improve understanding of the scattering properties of various hydrometer types. A high-performance mechanical polarization switch developed in ATD during FY 1997 was used for collecting polarization data. A CSU video disdrometer was used to measure precipitation particle characteristics, and snowfall records were collected at the Marshall test site. The PROWS data set consists of coordinated dual-polarimetric radar data, CSU campus microphysical data, video disdrometer data, and snow-gage measurements.
Tropical Ocean Climate Study (TOCS). The Japanese Marine Science and Technology Center (JAMSTEC) employed a state-of-the-art oceanographic research vessel, the R.V. Kaiyo, to conduct a field study in the western Pacific, an area characterized by mostly open ocean with a few scattered atolls and islands (Majuro to Palau). David Parsons (ATD/SSSF) used SABL on the R.V. Kaiyo to assist in studying the coupling between the upper ocean and the atmospheric mixed layer. SABL provided high-resolution measurements of mixed-layer changes and the evolution of non-precipitating clouds. With these data, Parsons will investigate the factors that control the diurnal variation of clouds and convection, including variations in the dynamic and kinetic controls on deep convection.
Cooperative Atmosphere-Surface Exchange Study (CASES-97). In this field study, S-Pol was located approximately 10 km from the Wichita, KS WSR-88D radar to determine the benefits of polarimetric radar measurements of precipitation. The radar was also used to study the low-level jet and boundary-layer evolution as part of the larger, multi-agency CASES project. Data from ten storm systems were collected during CASES, and over 200 hours of "clear-air" monitoring were conducted in support of the boundary-layer experiment. CASES PI Edward Brandes (NCAR/RAP) is comparing the differential phase and cross-polar correlation coefficient measurements from S-Pol in CASES-97 with results from a previous S-Pol test project east of Denver last year. RSF also fielded three S-Pol Bistatic receiver systems in an area east of Wichita as a demonstration and research project for the recovery of three-dimensional winds in real time. Co-investigators Tammy Weckwerth (RSF) and Josh Wurman (Univeristy of Oklahoma) headed up the Bistatic effort. Both the S-Pol and Bistatic deployments were implemented with software developed by the ATD Research Data Program (RDP). This real-time software allowed the monitoring of radar-estimated precipitation accumulations and the display of Bistatic wind vectors.
NEXRAD Anomalous Propagation Data Collection. The NEXRAD Archive 1 Recorder, developed by RSF, was deployed to gather I/Q time series data from the Memphis, TN NEXRAD radar. The Memphis site (along with many other sites) frequently experiences 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 complete, these algorithms will be implemented on the NEXRAD radar network.
Airborne Imaging Microwave Radiometer (AIMR). The Airborne Imaging Microwave Radiometer is a dual-frequency (90 GHz and 37 GHz) scanning radiometer. It was originally constructed for Atmospheric Environment Service (AES/CARD) in Canada for remote airborne measurements of surface ice. AES has loaned the radiometer to NCAR for the foreseeable future, and RSF is responsible for its improvement and support. FY 1997 efforts included characterization of the radio frequency circuitry and replacement of the onboard data system. The new data system consists of a SUN workstation for control and display, and a VxWorks computer on a VMEBus for real-time data gathering and control of the scanner.
S-Band Doppler Dual Polarimetric Radar (S-Pol). S-Pol was deployed for the PROWS program in East Lake, CO, and the CASES experiment in Wichita, KS. These two field programs proved the economy, reliability, and feasibility of S-Pol deployments. S-Pol generates an extensive array of polarimetric products in real time, including polarimetric rainfall-rate determinations. Data from these experiments are now being analyzed, and refinements to the radar and its software to improve future data quality are being made.
S-Pol Bistatic Receiver System. This system consists of three receiving antennas, radio data-transmission equipment, and real-time data-display software. The Bistatic system provides real-time multiple-Doppler radar measurements of winds using the S-Pol radar as a signal source. Jointly developed by RSF, University of Oklahoma, and ATD's Research Data Program, the system can be operated in the field on any S-Pol project.
Doppler on Wheels (DOW). RSF continued to collaborate with Josh Wurman of the University of Oklahoma on various signal-processing, antenna-control, and other technical improvements to the DOW radars.
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 effected a major upgrade to the 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.
DIAL Water-Vapor Profiling Lidar. During FY 1997, 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 profiling capabilities. Initial laboratory testing of the system is planned for early FY 1999.
Polarimetric Rainfall Estimation. Jim Wilson, J. Vivekanandan, Ed Brandes (NCAR/RAP), and Dick Oye (ATD/RDP) developed new precipitation accumulation products to supplement S-Pol’s polarimetric data products. This real-time capability was first used during the CASES field program near Wichita, KS.
SOLO Perusal and Editing Software. This year’s Solo release contained bug fixes and enhancements such as click-and-drag window resizing, and porting to Linux operating system.
GRID2PS. Susan Stringer and Wen-Chau Lee developed a PostScript-based contour and vector drawing software program that produces publication-quality, two-dimensional color or gray-scale figures from a variety of gridded datasets. GRID2PS reads CEDRIC files and can be easily customized to ingest any user-generated ASCII gridded dataset. Products from GRID2PS have already been used in a variety of ATD scientific publications and seminars.
TRACK-PLOT. Susan Stringer and Wen-Chau Lee developed this PERL program to plot aircraft tracks to assist investigators in identifying flight legs for mission review and research analysis. Track-Plot reads latitude, longitude, altitude, and time information from an ASCII file. Aircraft symbols, time, and altitude can also be plotted at a user-specified time interval.
NEXRAD Data Quality. Joe VanAndel continued development on the Archive 1 Recorder instrument that records time-series data from NEXRAD radars. The instrument can continuously record events that last for several hours to a collection of disks. This capability is being used to record phase-coded data for a range/velocity ambiguity reduction test, and for analysis of anomalous propagation problems.
Archive 1 Data Analysis Tool (A1Tool). Joe VanAndel continued development of the A1Tool to allow browsing and analysis of multi-gigabyte collections of time-series data. The A1Tool now uses a simple database to locate a particular record in a collection of files. A "bookmark" feature was recently added, allowing the user to note comments about a particular feature in the time series data, and save the current display configuration. This allows a user to later find a particular "feature", similar to how one uses bookmarks in a Web browser.
Anomalous Propagation (AP) Clutter Mitigation. Optimization of the fuzzy-logic recognition scheme was begun for intercomparison with the previous neural network scheme. Data from the Memphis WSR-88D, which is notorious for AP clutter, was taken with the A1 Data Recorder for detailed analysis and processing.
Range/Velocity Mitigation. In collaboration with NOAA's National Severe Storms Laboratory (NSSL), CSU, and the University of Colorado, RSF began investigating range and velocity mitigation techniques that might be applicable to the NEXRAD system. The project team developed a phase-coding scheme using spectrum analysis that spreads the interfering echoes equally across the Doppler spectrum and allows separation and recovery of that information. Phase-coded I/Q time-series data were collected at the Norman, OK, WSR-88D testbed radar using the RSF A1 Data Recorder for detailed analysis.
S-Pol Antenna Pattern Measurement. A limited set of S-Pol antenna pattern measurements was collected during the PROWS field experiment. S-Pol was located at the Eastlake site south of the Boulder Atmospheric Observatory (BAO) tower. A coherent source was placed on top of the tower and the antenna was scanned for recording azimuth-elevation radiation patterns. The antenna was scanned over a 36° sector in the azimuthal plane and a 10° sector in the elevation plane. Both vertical and horizontal polarization patterns were analyzed. As expected, the minimum in cross-polarization coincides with the maximum in co-polarization. The data were analyzed to determine the differential reflectivity (ZDR) bias and minimum linear depolarization return (LDR) that can be measured by S-Pol. Based on this analysis, the ZDR bias is 0.4 dB and the minimum detectable LDR is -27 dB.
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.
Lee also worked with Roger Wakimoto (UCLA) on a VORTEX squall-line/downburst study using ELDORA, WP-3Dand WSR-88D data.
Jim Wilson, in collaboration with Tom Keenan of the Australian Bureau of Meteorology Ma href="http://www.bom.gov.au"> (BoM) and Rit Carbone of NCAR/MMM, conducted research on the initiation and evolution of thunderstorms in northern Australia as part of the Maritime Continent Thunderstorm Experiment (MCTEX). These large thunderstorms, called Hector, are among the tallest in the world and result from convection forced by local sea breezes. These storms are found to 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.
Ed Brandes (NCAR/RAP), J. Vivekanandan, and Wilson collaborated on research efforts to refine techniques using polarimetric radar variables to estimate precipitation. S-Pol rainfall estimates derived in Colorado and Kansas were compared with rainfall estimates from nearby WSR-88D radars. The eventual goal is to add cost-effective dual-polarization capability to the national network of Doppler radars. During 15 January - 31 March 1997, a systematic collection of polarization-radar and snow-gauge datasets of winter precipitation was performed in collaboration with CSU investigators.
Tammy Weckwerth and Tom Horst (ATD/SSSF) have been analyzing Small Cumulus Microphysical Study (SCMS) data on the evolution of horizontal convective rolls. Data from the CP-2 radar are being combined with data from a Flux-PAM network, an ISS wind profiler, and a balloon sounder to determine the environmental parameters affecting roll formation, evolution, and dissipation.
Weckwerth and Shane Mayor (now University of Wisconsin-Madison) are examining data from the Flatland/LIFT project to examine small-scale linear streaks in the surface layer. Data from the DOW radar and the 2-µm Doppler lidar illustrate that the radar and lidar see features having distinctly different scales: the radar detects horizontal convective rolls with a horizontal wavelength of 1.25 km, while the lidar detects surface-layer linear streaks with a wavelength of 200 m.
Bruce Morley is working with SABL data to develop analysis techniques for extracting aerosol optical properties from the backscatter data.
Peter Hildebrand analyzed NCAR Electra and ELDORA data from TOGA COARE to investigate some rapidly changing and highly cellular shear-parallel rainbands. These rainbands consist of east-west elongated clusters of small convective cells, aligned with the low-level shear. Radar and aircraft in-situ data were used to investigate the structure and discrete propagation of these rainbands and to relate the speed of propagation to cold-pool flow. A connection was found between the observed increases in westerlies to the passage of the rainbands. These observations are in confirmatory agreement with the hypothesis that tropical westerly wind bursts are closely related to mesoscale convective processes.
Hildebrand collected NCAR Electra and ELDORA data during research flights in the FASTEX field program to study the mesoscale structure of frontal rainbands, as well as the structure, evolution, and movement of cold and warm fronts.
Hildebrand and Lee collaborated with Frank Marks (NOAA/HRD) and Robert Gall (NCAR/MMM) in research relating to hurricane structure, small-scale rainband features, and their relation to hurricane evolution; the remote measurement of location and movement of hurricane centers; and landfall effects and forecasting.
Volker Wulfmeyer continued his work on improving the 2-µm Doppler lidar: redesign of the slave oscillator with new pumps; characterization of the pumps for the slave; measurement of the thermal lensing of Tm:YAG; setup of a new, dynamically stable, resonator configuration; and specification of a new resonator.
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’s study was focused on simultaneous heterodyne water-vapor DIAL and Doppler wind measurements using the Mini-Mopa system (NOAA) and the 2-µm Doppler lidar (NCAR).
