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The Remote Sensing of Winds

Student: Paul Behrens. The Remote Sensing of Winds. Placement and monitoring of wind turbines. Supervisor: Stuart Bradley. Modern wind profiling and its problems, Remote sensing as a solution, SODAR remote sensing (Acoustic), LIDAR remote sensing (Laser),

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The Remote Sensing of Winds

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  1. Student: Paul Behrens The Remote Sensing of Winds Placement and monitoring of wind turbines Supervisor: Stuart Bradley

  2. Modern wind profiling and its problems, Remote sensing as a solution, SODAR remote sensing (Acoustic), LIDAR remote sensing (Laser), New design bi-static SODAR, phased array, Other applications, Summary. Outline

  3. The Placement and Monitoring of Wind Turbines • Problems: • Building Met masts for site profiling studies becomes cost prohibitive in an era of large turbine designs. • Requirements for mast planning permission slows procedures. • For complete profiling of all turbine placements many masts or mast movements are needed. • The cost of moving a portable mast is > $30,000. • $30,000 is the cost of one remote wind profiling instrument (a SODAR) • Offshore profiling. Riso, Denmark

  4. The Solution: Remote Sensing • Two dominant types of remote sensing instrument: • SODAR (SOund Detection And Ranging) or LIDAR (Light Detection And Ranging) Remote sensing instruments work on Doppler principles: 1. Transmit energy toward air parcel, 2. Some energy is reflected from air parcel, 3. Detect Doppler shift in phase (SODAR) or colour (LIDAR), 4. Estimate wind velocity component toward instrument, 5. Repeat process in two more directions for all 3 wind speed components, 5. The whole process is repeated for different heights. Horizontal wind Transmitter & receiver

  5. SODAR Technology • Utilizes the reflection of sound from turbulence. • Three beams using three antennas or phased array. • Majority of SODARs monostatic, i.e. Transmitter and receiver co-located. SODAR problems: - Low turbulence == low data availability, - Reflections of acoustic pulses from buildings, turbines etc. - Tilted beams can sample different winds in complex terrain.

  6. Cup vs SODAR residuals Cup vs Cup residuals SODAR Accuracy With proper calibration very little deviation from cup residuals. Slight under estimation wind speeds of 16 m/s and above? Cup vs Cup - Two anemometers sampling the same air parcel

  7. LIDAR Technology Use particulates in atmosphere for Doppler shift. - Similar accuracy to SODARs Two major manufactures of LIDAR: Qinetiq: • Scan Conically • Continuous beam Leosphere: • Scan in N-E-S-W steps. • Pulsed beam LIDAR problems: • In clear air, no particulates for reflection, • High cloud gives false data. (Qinetiq) • Tilted beams sample different winds, • Low spatial resolution above hub height (Qinetiq)

  8. The Tilted Beam Problem Tilted beams don’t sample the same winds in complex terrain Could be significant in New Zealand!

  9. The Bi-static SODAR: Separated Transmitter and receiver modules Advantages: • Solves the tilted beam problem • Able to use microphones instead of speaker to receive pulse return, • Echo strength from air parcels greater (due to additional echo from ) • Overall signal levels increase by 20-40dB. (100x increase in signal to noise). • 5m vertical resolution – better than existing SODAR and LIDAR systems Horizontal wind 5-200m Transmitter 40m Receivers – two phased arrays

  10. Progressive phase shift in memory Voltages sampled at t   Phased Array Receiver Use static array of microphones. Use software based phase shifting to receive signals from different angles. Combine signals from each phase shift for specific height. The two previous bi-static instruments looked at one height only………..

  11. Current Work Software: • Work with ADC board to obtain 12 channels of microphone data. • Repeat triggering of listening. Hardware: • Finding proto-type 12 microphone array beam pattern. • Making cables Theory: • Other meteorological applications?

  12. Other Applications: Monitoring of incoming wind profile: • With knowledge of incoming wind profile we can actively control blade pitch • Increases power performance and reduces mechanical fatigue • Mount LIDAR/Speaker on nacelle of wind turbine SODAR LIDAR Phased array Challenges: vibrations and noise

  13. Other Applications: Monitoring the endangered Kokako bird • Kokako monitoring direct, intrusive and human intensive. • Replace direct monitoringuse two phased arrays and triangulate Kokako position. • Remotely monitor Kokako movements. • Challenges: Kokako acoustic signature, Scanning in software, Signal processing and background noise, Phased array beam pattern

  14. The Future • Complete profiling coverage of potential wind speed sites. • Knowledge of incoming wind profile with real-time blade pitch control. • Bi-static development a possible key instrument in increasing accuracy and coverage.

  15. Thanks!!

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