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.