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Principles of Wind Profiler Operation Wind Profiler Training Manual

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Principles of Wind Profiler Operation Wind Profiler Training Manual 9 nts LIBRARY g P R I N C I P D P R O F I L E R OPE w TRAINING MANUAL NUMBER ONE : V* PREPARED FOR THE OFFICE OF METEOROLOGY NATIONAL WEATHER SERVICE fe no BY THE PROGRAM FOR REGIONAL OBSERVING AND FORECASTING SERVICES ENVIRONMENTAL RESEARCH LABORATORIES NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION PROFILER TRAINING MANUAL #1 Principles of Wind Profiler Operation Developed for the National Weather Service Office of Meteorology J 1 o s Lb: jul < r I? -J Douglas W. van de Kamp SIS. DOT OHMUMBT Profiler Program NOAA/ERL Boulder, Colorado (yw Poc, , c March 1988 55. 2 ■■ W NOTICE Mention of a commercial company or product does not constitute an endorsement by NOAA Environmental Research Laboratories. NOAA does not authorize, for publicity or advertising, the use of any information from this publication concerning proprietary products or the tests of such products. 11 Author's Preface In the past decade, wind profilers have evolved from individual atmospheric research systems to a 30-site demonstration network which will be installed in the central United States by mid 1990, called the Wind Profiler Demonstration Network (WPDN). Although the research community has been observing wind profiler data for over five years, we have not explored all their uses, This manual is the first in a series of four manuals and videotapes summarizing our current experience with the operation, quality control, and meteorological use of wind profiler data. I would like to thank Tom Schlatter of the Program for Regional Observing and Fore­ casting Services (PROFS) and Fred Zbar, Brian Smith, Dan Smith, Joe Schaefer, Andy Edman, and Larry Dunn of the National Weather Service for their constructive reviews and comments. Thanks also to the Wind Profiler Research group of the Wave Propaga­ tion Laboratory for supplying the profiler data presented in this manual. - Ill Contents 1. Introduction and Short History of Wind Profilers ................................................... 1 1.1. What is a Wind Profiler?...................................................................................... 1 1.2. From Early Research Systems to the Present Development of a 30-Station Demonstration Network........................................................................................ 1 1.3. Description and Uses of Wind Profiler Data........................................................ 2 1.4. Advantages and Disadvantages of the Wind Profilers..........................................6 2. Principles of Operation ................................................................................................... 8 2.1. System Hardware ................................................................................................... 8 2.1.1. Transmitter and power supply ................................................................ 8 2.1.2. Antenna......................................................................................................... 9 2.1.3. Receiver and computer.......................................................................... 10 2.2. Antenna Configuration........................................................................................ 11 2.2.1. Number of beams needed .................................................................... 11 2.2.2. Pointing angles of each beam .............................................................. 12 2.2.3. How a phased array works.................................................................... 13 2.3. Use of Atmospheric Turbulence as a Measure of the Mean Wind ............ 15 2.3.1. Scales of turbulence .............................................................................. 15 2.3.2. Doppler shift............................................................................................. 15 2.4. The Doppler Signal Spectrum and Its Uses .................................................... 15 2.4.1. Returned power estimate........................................................................ 16 2.4.2. Radial velocity estimate.......................................................................... 16 2.4.3. Spectral width estimate.......................................................................... 17 2.5. From Radial Components to Horizontal Winds................................................ 17 3. Accuracy and Limitations of Wind Profiler Data .................................................... 20 3.1. Assumption of Uniformity of the Wind Field Across All Beams ..................... 20 3.2. Increased Signal-to-noise Ratio by Time-averaging .......................................... 21 3.3. Internal Electronic Noise....................................................................................... 21 3.4. External Electronic Noise ..................................................................................... 21 3.5. Side Lobes..............................................................................................................23 3.6. Precipitation and Vertical Velocity Correction.................................................... 23 3.7. Effect of Aircraft on the Data...............................................................................24 3.8. Expected Accuracy............................................................................................... 24 3.8.1. Profiler vs. rawinsonde .......................................................................... 24 3.8.2. Profiler vs. lidar ......................................................................................... 25 3.8.3. Profiler vs. profiler .....................................................................................25 4. Practical Information on the 30-Station Demonstration Network ......................27 4.1. Location of Profiling Sites.....................................................................................27 4.2. Products, Schedules, and Communications ...................................................... 27 4.3. Effects of Minimizing Satellite Interference .........................................................28 4.4. The Hub..................................................................................................................30 V 4.5. Expected Height Coverage...................................................................................31 4.6. Mean Time Between Failure (MTBF).................................................................. 31 4.7. Mean Time To Repair...........................................................................................32 4.8. Hub Failure..............................................................................................................32 5. References..................................................................................................................... 33 Appendix A. A Detailed Look at the Doppler Signal Spectrum...............................35 Appendix B. Examples of Wind Profiler Data................................................................40 VI 1. Introduction and Short History of Wind Profilers 1.1. What is a Wind Profiler? A wind profiler is a Doppler radar used to measure the atmospheric winds above a profiler site. Typical operation of a wind profiler produces a vertical profile of the winds every hour from near the Earth's surface to above the tropopause. The WPDN wind profilers are designed to operate reliably and unattended in nearly all weather conditions. To achieve this reliability, they have a minimum number of moving parts; therefore a fixed beam antenna is used. Obtaining wind profiles consistently to the tropopause in nearly all weather conditions requires the use of a relatively long wavelength radar. Typical NWS weather radars that have been operational for the past 30 years operate with wavelengths of 10 cm or less and require cloud or precipitation particles to act as reflectors. Wind profilers are relatively low-power, highly sensitive clear-air radars, operating with wavelengths from 33 cm to 6 meters. The radars detect fluctuations in atmospheric density, caused by the turbulent mixing of volumes of air with slightly different temperature and moisture content. The resulting fluctuations of the index of refraction are used as a tracer of the mean wind in the clear air. Although re­ ferred to as clear-air radars, wind profilers are capable of operating in the presence of clouds and precipitation. 1.2. From Early Research Systems to the Present Development of a 30-Station Demonstration Network Early radars (1920's-30's) were used primarily for upper atmospheric research con­ cerning the ionosphere. World War II sped the development and use of short wave­ length radars. It was not until the late 1960's and early 1970's that the potential for us­ ing sensitive clear-air radars to study the lower atmosphere became apparent. Chad­ wick and Gossard (1983) give an excellent account of the developments in clear-air radars. In the late 1970’s, the Aeronomy Laboratory of the Environmental Research Laborato­ ries (ERL) in Boulder, Colorado, built and tested a very high frequency (VHF) 50-mega­ hertz (MHz) radar near Platteville, Colorado. This radar was a scaled-down prototype of a Mesosphere-Stratosphere-Troposphere (MST) research radar built and operated near Poker Flat, Alaska. In 1980, the Wave Propagation Laboratory (WPL) of ERL began operation of the Platteville radar jointly with the Aeronomy Laboratory to measure tropospheric winds. This system operated for several years and produced coarse vertical resolution wind profiles.
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