Continuous-wave bistatic laser Doppler wind sensor

Abstract

A coherent laser radar has been built by use of a master-oscillator power-amplifier arrangement in which the master oscillator is an external-cavity semiconductor laser and the power amplifier is an erbium-doped fiber amplifier with approximately 1-W output at a wavelength of 1.55 microm. The beams are routed within single-mode optical fiber, allowing modular construction of the optical layout with standard components. The system employs separate transmit and receive optics (a bistatic configuration) and has sufficient sensitivity for reliable Doppler wind-speed detection in moderate scattering conditions at short range (to as much as approximately 200 m). The bistatic arrangement leads to a well-defined probe volume formed by the intersection of the transmitted laser beam with the virtual backpropagated local-oscillator beam. This could be advantageous for applications in which the precise localization of wind speed is required (e.g., wind tunnel studies) or in which smoke, low cloud, or solid objects can lead to spurious signals. The confinement of the probe volume also leads to a reduction in the signal power. A theoretical study has been carried out on the reduction in wind signal strength compared with the monostatic arrangement, and the results are compared with experimental observation.

Lidar for Turbine Control: March 1, 2005 - November 30, 2005

“…While more light is scattered from aerosols at shorter wavelength, long wavelength systems are inherently more sensitive [16] (reasons include the emission of more photons per Watt of laser power and reduced Doppler shifts leading to lower noise bandwidth). These effects largely cancel, leaving an overall dependence in SNR of order λ 0.5 in the relevant weak signal regime of low β(π).…”

“…New developments in optical fiber and related components from the telecommunications industry offered a promising approach to lidar construction. The team successfully demonstrated CW all-fiber lidar anemometers (at a wavelength 1.55µm) in the late 1990s [9,16] and have remained at the forefront with the development of a commercial fiber lidar system (ZephIR) that has an established track record of successful wind measurement in a number of applications related to the wind power industry [17][18][19][20][21].…”

Monostatic coaxial 15 μm laser Doppler velocimeter using a scanning Fabry-Perot interferometer

“…Both employ a commercial off-the-shelf scanning Fabry-Perot interferometer (FPI 100, Toptica Photonics AG). Unlike in a previous sFPI-LDV demonstration with bistatic or biaxial design [8], our setups use monostatic coaxial arrangement that provides for easy alignment and better receiver efficiency. Instead of photon counter, we use an InGaAs photodetector with built-in transimpedance amplifier (LCA-S femtowatt photoreceiver, FEMTO GmbH).…”

“…In addition, we employ a monostatic coaxial architecture to achieve high optical receiver efficiency and easy alignment, which are the main drawbacks in bistatic or biaxial designs [8]. The use of sFPI in Doppler velocimetry was first demonstrated by Jackson and Paul in 1970 [9].…”

Wind Turbine Wake Characterization from Temporally Disjunct 3-D Measurements

“…Currently, new technologies are being developed that allow for more flexible scanning geometries [2,11], thus broadening the application range of such systems [12] and exploiting the measuring potential of multiple LiDAR arrays [13]. While cw LiDARs can sample at very short ranges, they are typically limited to distances <200 m because the effective probe volume increases to the fourth power of the focus range [14], thus increasing the uncertainty in the wind speed measurements away from the instrument [15].…”