Research Group
"Optical Remote Measurements - Analysis of Atmospheric Processes with Optical Methods"

Doppler-Windlidar WiLi

Motivation

Vertical and horizontal transport processes control the large-scale distribution of particles and trace gases in the atmosphere. Pollutants which are transported from the planetary boundary layer to the free troposphere by vertical fluxes may be distributed over tens of thousands of kilometres, cross the oceans, and travel from one continent to another. From this point of view, vertical fluxes are of great interest in atmospheric research. The determination of vertical fluxes requires the measurement of the vertical wind component with high accuracy (<0.1 m/s) and high temporal resolution (<10-30 s).

Such measurements are possible with Doppler wind lidar. To complement our instruments, we have developed a pulsed coherent Doppler lidar. The eye-safe 2-µm lidar measures atmospheric vertical wind fields with high spatial and temporal resolution (50-100 m, 10-30 s) and high accuracy (<0.1 m/s error of vertical velocity). The use of the new lidar in combination with the existing IfT lidars shall allow us to investigate transport and mixing processes in the lower atmosphere in detail. The potential was shown during a joint measurement campaign with the Doppler wind lidar of the Max Planck Institute for Meteorology Hamburg in fall 2003.

Instrument

WiLi is a coherent Doppler wind lidar for:

1. measurement of vertical wind velocity with high precision
2. investigation of vertical transport processes in the planetary boundary layer and the lower free troposphere (in combination with multiwavelength lidar systems)
3. measurement of horizontal wind by use of a 3D Beam steering unit.

Setup

		Specifications Wind speed accuracy: 10 cm/s Maximum wind speed: ± 20 m/s Maximum height: 15 km Spatial resolution: 75 m Temporal resolution: 1-5 s
Master Oscillator Laser crystal: Tm:LuAG Design: near-hemispherical Wavelength: 2022.5 nm Power: 25 mW	Power Oscillator Laser crystal: Tm:LuAG Design: L-shaped Pulse energy: 1.5 mJ Pulse repetion rate: 750 Hz Frequency offset: 80 MHz Frequency stability: ±1 MHz Pulse duration: 450 ns Chirp: 0.95 MHz/µs	Transceiver Type: off-axis Mersenne Free aperture: 140 mm Photodetector: InGaAs, 75 µm diameter	Data Acquisition Preamplifier: DC - 200 MHz, 20 kV/A Digitizer: PCI, 8 bit, 250 MS/s Computer: two 2.8-GHz processors Data processing: 15 km@1 kHz, 75 m resolution

Measurements

Development of vertical wind speed in a convective planetary boundary layer and a lofted aerosol layer.	Backscatter signal and vertical wind speed during the passover of a rotating wall cloud with strong dispersion of dust .	Observation of an internal gravity wave at the top of the planetary boundary layer and of the fall speed of ice-crystalls in an altocumulus cloud.

top of page