Imaging doppler lidar for wind turbine wake profiling
An imaging Doppler lidar (IDL) enables the measurement of the velocity distribution of a large volume, in parallel, and at high spatial resolution in the wake of a wind turbine. Because the IDL is non-scanning, it can be orders of magnitude faster than conventional coherent lidar approaches. Scattering can be obtained from naturally occurring aerosol particles. Furthermore, the wind velocity can be measured directly from Doppler shifts of the laser light, so the measurement can be accomplished at large standoff and at wide fields-of-view.
1. An imaging Doppler lidar, comprising:
a laser transmitter that provides a pulsed, narrow linewidth laser light to flood illuminate a scene comprising aerosol particles moving at a velocity,
a frequency discriminator for measuring the Doppler frequency shift of laser light scattered from the moving aerosol particles, and
at least one imaging receiver for detecting the scattered laser light and having a variable gate delay at the repetition frequency of the laser transmitter for range-gating the detected scattered laser light.
2. The imaging Doppler lidar of claim 1 , wherein the laser transmitter has a repetition rate of greater than 1 Hz.
3. The imaging Doppler lidar of claim 1 , wherein the laser transmitter comprises a Q-switched solid-state laser.
4. The imaging Doppler lidar of claim 1 , wherein the laser light has a pulse width of less than 10 nanoseconds.
5. The imaging Doppler lidar of claim 1 , wherein the laser light has a wavelength of between 300 and 1500 nanometers.
6. The imaging Doppler lidar of claim 1 , wherein the laser light has a linewidth of less than 200 MHz.
7. The imaging Doppler lidar of claim 1 , wherein the frequency discriminator can discriminate a Doppler frequency shift of the scattered laser light of less than 100 MHz.
8. The imaging Doppler lidar of claim 1 , wherein the frequency discriminator comprises a single-edge spectral absorption filter.
9. The imaging Doppler lidar of claim 1 , wherein the frequency discriminator comprises a gas absorption cell.
10. The imaging Doppler lidar of claim 1 , wherein the at least one imaging receiver has a gate width of less than 10 ns.
11. The imaging Doppler lidar of claim 1 , wherein the at least one imaging receiver is not on a line-of-sight with the laser transmitter.
12. The imaging Doppler lidar of claim 1 , wherein the at least one imaging receivers comprises at least three imaging receivers, thereby providing a vector velocity image of the scene.
13. The imaging Doppler lidar of claim 1 , wherein the at least one imaging receiver comprises a focal plane array.
14. The imaging Doppler lidar of claim 1 , wherein the scene comprises a wind wake downstream from a wind turbine.