Development and testing of a triplebeam Doppler lidar
Development and testing of a triple-beam Doppler lidar system for 3 D wind measurement 19 th Coherent Laser Radar Conference 18 th - 21 st June 2018, Okinawa, Japan Matthew S. Warden (a), Simon T. Sørensen (a), John Macarthur (a), Mark Silver (b), Theodore C. Holtom (c), Craig Mc. Donald (d), Peter Clive (d), Henry T. Bookey (a) Fraunhofer Centre for Applied Photonics, Technology and Innovation Centre, 99 George Street, Glasgow G 1 1 RD, UK (b) Thales UK, 1 Linthouse Road, Glasgow, G 51 4 BZ, UK (c) Wind Farm Analytics Ltd. , 2/1, 3 Queens Park Avenue, Glasgow, G 2 5 LD, UK (d) Wood, Floor 2, St Vincent Plaza, 319 St Vincent Street, Glasgow, G 2 5 LD, UK Lead Author e-mail address: matthew. warden@fraunhofer. co. uk © Fraunhofer
Introduction: What is this talk about? © Fraunhofer
Fraunhofer Centre for Applied Photonics © Fraunhofer
Converging beams concept: Information gained from a single lidar measurement cation nt lo e m e r u s Mea ed measur true For 3 D wind measurement, combine ≥ 3 measurements, with different beam directions. © Fraunhofer city ‘line velo ’ t h g i s of win dv elo city
Combining beams concept: Two options for multiple beam directions Diverging lidar 1 lidar large measurement volume sequential measurements © Fraunhofer Converging lidar 3 lidars small measurement volume simultaneous measurements
Lidar Design Lidar head Remote unit Central unit © Fraunhofer
Lidar Design We have combined common functions where possible. © Fraunhofer Parameter Value Wavelength 1550 nm Pulse duration 200 ns Pulse energy 6 μJ Pulse repitition rate 20 k. Hz Telescope diameter 50 mm Beam steering anglular range +/- 60 degree cone
Control PC and Digitiser Shared control PC • good for synchronisation of lidar functions • fast PC required for analysis (3× the data) Shared Digitiser • good timing synchronisation © Fraunhofer
Optical amplifier design © Fraunhofer
Optical amplifier design § Seed laser shared between 3 lidar heads § Good for synchronisation and low cost § Adds complexity, no redundancy § SBS limits pre-amp power: power amps required close to telescopes © Fraunhofer
Laser system Seed laser § < 5 k. Hz linewidth § 1550. 12 nm, 80 m. W, linear pol. AOM (x 2) § Pulse modulation: 200 ns, 20 k. Hz § Self heterodyne freq. shift Preamp § Core pumped PM fibre Power amp § Cladding pumped PM fibre x 3 © Fraunhofer
Power amp © Fraunhofer § Power limited to ~120 m. W by SBS in >1 m fibre between amplifier and circulator § Can be improved with various techniques (or shorter fibre length) § Don’t need high power / long range
Stimulated Brillouin Scattering (SBS) Increasing pump power Signal Backscattered light § Coupling of optical fields and acoustic waves (phonons) § At high powers: traveling refractive index grating backscatters the signal © Fraunhofer
Testing © Fraunhofer
Comparison of measured wind speed © Fraunhofer
Comparison of measured wind speed Lidar-Lidar Comparison © Fraunhofer Lidar-Mast Comparison
Test of intersecting beam measurements © Fraunhofer
Test of intersecting beam measurements (bottom) Measured 1 -minute averaged LOS velocities of the converging lidar beams. (middle) Reconstructed velocities in the (east, north, vertical) reference frame and (top) wind speed and direction. © Fraunhofer
Summary 1. Converging beam concept 2. Lidar design 3. Test results © Fraunhofer
© Fraunhofer
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