System Evaluation of an Incoherent Wind Doppler LIDAR Using an Iodine Filter

Abstract

This study is carried out system error evaluation of an incoherent wind Doppler LIDAR system that uses an iodine filter. Sharp slopes of an iodine filter provide better wind-measuring sensitivity than a Fabry-Perot etalon. The magnitude and sign of the Doppler shift are obtained from the ratio of the intensities of two signals arising from two slopes of an iodine absorption line. Systematic errors of wind measurement are caused mainly by the fluctuations of laser frequency and iodine absorption linewidth. The standard deviation of the zero Doppler shift is experimentally evaluated to be 1.8 MHz, which corresponds to the uncertainty in line-of-sight wind velocity of 0.5 m/s. This result shows a good agreement with the result of an experiment of the tuning stability of laser frequency with respect to the absorption line slope. Moreover, comparison of wind profiles is made between the Doppler LIDAR and concurrent radiosonde measurements. The measured horizontal wind speeds are from 8 to 21 m/s in the altitude range from 8 to 25 km, indicating a reasonable agreement between the two instruments. Experimentally, the total optical efficiency of this Doppler LIDAR system is estimated to be 4.0%, which is close to the value expected from the evaluation of each component of the instrument.

Low-Altitude Wind Measurement Using Incoherent Doppler Lidar by Utilizing Both Absorption Slopes of the Iodine Absorption Spectrum

“…Figure 1 shows a schematic diagram of our previously proposed incoherent Doppler lidar using an iodine absorption spectrum for the upper troposphere and stratosphere. 8) The Doppler lidar system consists of a pulsed, frequencydoubled Nd:YAG laser that is injection-seeded by a CW Nd:YAG laser, and a receiving unit. The oscillation frequency of a narrowband laser switches alternately from the frequency 1 on one slope of the iodine absorption spectrum to the frequency 2 on the other slope using two AO shifters; 1 and 2 are shown in Fig.…”

“…7) We have proposed an incoherent Doppler wind lidar using an iodine absorption spectrum for wind measurement in the upper troposphere and stratosphere. [8][9][10] The laser used is an injection-seeded Nd:YAG laser (532 nm wavelength), and the laser frequency alternates between intermediate points ( 1 and 2 ) of the slopes of an absorption line of iodine absorption spectrum. Doppler-shifted velocity is obtained from the ratio of the intensities of the two transmission signals.…”

Flow Velocity Measurement Using an Orthogonally Radiated Ultrasonic Beam

“…Many physical measurement methods and applications utilizing the Doppler effect have been proposed or implemented in acoustic [1][2][3][4] and optical [5][6][7][8][9] domains. When Doppler flowmetry is applied to the velocity measurement of flow in a pipe, normally the transducer needs to be fixed oblique to the flow as the ultrasonic beam axis has an angular component that is parallel to the flow direction.…”