The Remote Sensing of Winds

Student: Paul Behrens

Placement and monitoring of wind turbines

Supervisor: Stuart Bradley

Outline

● 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.

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

The Solution: Remote Sensing

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.

• Two dominant types of remote sensing instrument:

• SODAR (SOund Detection And Ranging) or LIDAR (Light Detection And Ranging)

Horizontal wind

Transmitter & receiver

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.

SODAR Accuracy

Cup vs SODAR residuals

Cup vs Cup residuals

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

LIDAR TechnologyUse particulates in atmosphere for Doppler shift. - Similar accuracy to SODARs

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)

Two major manufactures of LIDAR:

Qinetiq: • Scan Conically• Continuous beam

Leosphere:• Scan inN-E-S-W steps.• Pulsed beam

The Tilted Beam Problem

Tilted beams don’t sample the same winds in complex terrain

Could be significant in New Zealand!

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

Transmitter

Receivers – two phased arrays

2VC

40m

5-200m

The Bi-static SODAR: Separated Transmitter and receiver modules

Phased Array Receiver

Voltages sampled at t

Progressive phase shift in memory

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………..

Current WorkSoftware:• 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?

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

LIDAR SODAR

Phased array

Challenges: vibrations and noise

Other Applications:

• Kokako monitoring direct, intrusive and human intensive.

• Replace direct monitoring use two phased arrays and triangulate Kokako position.

• Remotely monitor Kokako movements.

• Challenges:

Kokako acoustic signature,

Scanning in software,

Signal processing and background noise,

Monitoring the endangered Kokako bird

Phased array beam pattern

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.

Thanks!!