Exploration of Whole Atmosphere Lidar: Mach-zehnder Receiver to Extend Fe Doppler Lidar Wind Measurements from the Thermosphere to the Ground

Abstract

A receiver employing a field-widened Mach-Zehnder interferometer (MZI) is investigated for extending the wind measurement range of a narrowband Fe Doppler (372 nm) lidar from its existing measurement range in the mesosphere and lower thermosphere (MLT) down to the ground. This design uses the multiple transmitted frequencies available from the base Fe Doppler lidar in combination with an MZI receiver to make a measurement of the Doppler shift from Rayleigh-Mie scattering that is independent of aerosol backscatter ratio, temperature and pressure of the lidar volume and also independent of geometric overlap, the chopper function and any other factor affecting the signal in both MZI channels equally. A ratio is constructed from the three frequencies and two channels of the interferometer that exhibits a measurement performance of 1.75 times the Cramer-Rao lower bound, which is comparable to the dual MZI (DMZ) while preserving the insensitivity to backscatter spectrum of the quad MZI (QMZ). Using actual data obtained recently from the Fe Doppler lidar, we show the expected measurement performance of this whole atmosphere lidar instrument concept.

Detection of Atmospheric Wind Speed by Lidar Based on Quadrichannel Mach–Zehnder Interferometer

“…Combined with R β = (M p − M m )/(M p − Q S ), the standard deviation of radial wind speed measurement(See Appendix A.3.) can finally be obtained as follows [13][14][15][16]:…”

“…Because the output fiber of the experiment is short, it cannot ensure good mode mixing and good beam depolarization; thus, the mode scrambler can be inserted into the output of the fiber coupler before being injected into the interferometer. Four avalanche photodiodes and differential amplifiers (AD8138) used to detect the interferometer output signals ensure the detection accuracy of the signals, and the signals are collected by 16 Figure 2b shows the optical transmission schematic diagram of the laser radar (the figure shows an off-axis transceiver system, which is a coaxial transceiver system when the transmitted beam is in the geometric center of the receiving telescope). In the figure, the transmitting laser emits a Gaussian beam into the atmosphere.…”