Coherent Doppler Lidar (CDL) has garnered significant attention for its remote sensing capabilities and high accuracy, establishing it as a pivotal technology in environmental monitoring. The dynamics of airborne platforms are intricately linked to wind conditions, making airborne CDL a crucial tool for enhancing aviation safety. Additionally, airborne CDL systems provide comprehensive meteorological data across extensive geographical areas. We introduce an all-fiber Continuous-Wave (CW) CDL system specifically engineered for integration with flight instrumentation. This CDL system excels in measuring and reconstructing critical flight parameters such as True Airspeed (TAS), Angle of Attack (AoA), and sideslip angle (AoS). A key feature of the CW CDL system is providing three-dimensional airspeed measurements at a data rate of 50 Hz, capturing data from a position 30 meters ahead of the aircraft. To ensure the accuracy and reliability, a series of verification experiments were conducted. Initially, ground-based comparison experiments were performed using a wind tunnel, a wind tower, and a vehicle-mounted sonic anemometer. For airborne verification, the lidar was installed on an aircraft. The aircraft flew at three different indicated airspeeds and four different altitudes, enabling a comprehensive comparison between flight instrument speed data and the results obtained from the CW CDL system. The linear analysis of these airborne experiments consistently yielded correlation coefficients exceeding 0.97, with the mean deviation of less than 1 m/s.
A 2 μm single-frequency, all-solid-state laser is one of the preferred light sources for coherent laser wind lidar and differential absorption lidar. In order to obtain 2 μm single frequency pulse laser with the high energy and hundred nanoseconds pulse width, the Ho:YAG non-planar ring cavity laser pumped by Tm:YLF solid state laser was used as the seed source to design and develop an injection-seeding single frequency Q-switched Ho:YAG pulse laser. A 2090 nm single-frequency pulse laser with an average pulse energy of 18.51 mJ and pulse width of 110.9 ns was obtained at a repetition rate of 200 Hz. The beam quality M2 factors of the output laser are 1.16 in the X direction and 1.25 in the Y direction, and the pulse spectrum width is 4.05 MHz.
A1645nm injection-seeded Q-switched Er:YAG ceramic laser pumped by a 1532 nm fiber laser with changeable pulse repetition frequency (PRF) used for Coherent wind measurement Lidar is demonstrated. Single-frequency operation of Er:YAG laser is achieved by injection seeding technique. A ‘M-shape’ ring cavity is utilized to eliminate the effects of spatial hole burning. The laser delivered single-frequency pulses with energy ranging from 6.6 to 10.2 mJ. The corresponding pulse width and PRF varied between 179 ns-271 ns and 300 Hz-1 kHz, respectively. And the line width at 300 Hz is measured to be 2.82 MHz. The measured M2 factors are 1.51 and 1.54 in x and y directions, respectively.
Long-range wind sensing using coherent Doppler lidar is attractive in many fields such as wind shear warning, aerosol detection and aircraft wake vortex detection. Recently, single frequency, all-solid-state laser around 1.6 μm has caused great interests for its eye-safety and high pulse energy. Velocity accuracy which is one of the key factors of wind lidar systems needs to be calibrated. The 1645 nm eye-safe coherent Doppler wind lidar based on injection-seeded technique consists of laser systems, transceiver optics, and data processing systems is developed. The average power of the laser pulses is 2.6 W with a pulse width of 190 ns at a repetition rate of 300 Hz. The accuracy of velocity measured by the lidar system is calibrated with a velocity calibrator based on a servo motor with a maximum speed of 3000 r/min and a rotating disk with a diameter of 300 mm. A real-time display software based on the LabVIEW platform is designed to get the velocity results and signal to noise ratio (SNR) from the FPGA acquisition module, and the central frequency correction algorithm is used to eliminate frequency jitter of the laser. To calibrate the wind velocity near 0 m/s, a nonmoving hard target at the range of 1.2 km with an elevation angle of about 0.5 deg is measured. Results show that a velocity accuracy (standard deviation of the measurement errors) of 0.38 m/s in the range ±40 m/s and the accuracy of zero velocity is 0.16 m/s.
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