All-fiber upconversion high spectral resolution wind lidar using a Fabry-Perot interferometer

摘要

An all-fiber, micro-pulse and eye-safe high spectral resolution wind lidar(HSRWL) at 1550nm is proposed and demonstrated by using a pair of upconversionsingle-photon detectors and a fiber Fabry-Perot scanning interferometer(FFP-SI). In order to improve the optical detection efficiency, both thetransmission spectrum and the reflection spectrum of the FFP-SI are used forspectral analyses of the aerosol backscatter and the reference laser pulse. Thereference signal is tapped from the outgoing laser and served as a zerovelocity indicator. The Doppler shift is retrieved from a frequency responsefunction Q, which is defined as the ratio of difference of the transmittedsignal and the reflected signal to their sum. Taking advantages of highsignal-to-noise ratio of the detectors and high spectral resolution of theFFP-SI, the Q spectra of the aerosol backscatter are reconstructed along theline-of-sight (LOS) of the telescope. By applying a least squares fit procedureto the measured Q spectra, the center frequencies and the bandwidths areobtained simultaneously. And then the Doppler shifts are determined relative tothe center frequency of the reference signal. To eliminate the influence oftemperature fluctuations on the FFP-SI, the FFP-SI is cased in a chamber withtemperature stability of 0.001 during the measurement. Continuous LOS windobservations are carried out on two days at Hefei (31.843 N, 117.265 E), China.In the meantime, LOS wind measurements from the HSRWL show good agreement withthe results from an ultrasonic wind sensor (Vaisala windcap WMT52). Due to thecomputational expensive of the convolution operation of the Q function, anempirical method is adopted to evaluate the quality of the measurements. Thestandard deviation of the wind speed is 0.76 m/s at the 1.8 km. The standarddeviation of the retrieved bandwidth variation is 2.07 MHz at the 1.8 km.