National Institute of Information and Communications Technology (NICT) has made efforts in order to develop a 2-μm coherent lidar for measuring CO2 concentration and line-of-sight (LOS) wind speed. Experimental horizontal CO2 measurements were made to examine the detection sensitivity of the 2-μm coherent lidar in April and May, 2008, and October, 2009. Experimental vertical CO2 measurements were made for the Greenhouse gas Observing SATellite (GOSAT) data products validation in February 2010 and in January and February 2011. Bias and random error in the LOS wind speed measurements were also investigated in order to evaluate of the 2-μm coherent lidar for wind measurements in 2010. In the paper, we present an overview of our 2-μm coherent lidar developed at the NICT and also of the experimental results.
A coherent 2-μm differential absorption and wind lidar (Co2DiaWiL) has been built with a high power Q-switched
Tm,Hm:YLF laser to measure CO2 concentration and radial wind velocity. Our experiment was conducted to test the
ability of the Co2DiaWiL to make wind measurement in the atmospheric boundary layer and lower free troposphere. The bias in the velocity measurement was estimated as –0.0069 m/s using measurements from a stationary hard target. The magnitude of the random error of radial velocity measurements was determined from data in the vertical pointing mode and the Co2DiaWiL achieved a velocity precision of 0.12 m/s. The radial velocity measurements to ranges up to 20-25 km by the horizontally fixed beam mode for average times of 1 min have been demonstrated with the high laser output power. The Co2DiaWiL-measured radial velocities were directly compared with the wind speeds measured by a closelylocated sonic anemometer. The correlation coefficient was as large as 0.99 for comparison of radial velocities averaged for 1 min from the Co2DiaWiL and sonic anemometer.
We developed a coherent 2-μm differential absorption and wind lidar to measure CO2 concentration and line-of-sight
wind speed. The wavelength of on-line laser was set at the R30 absorption line center of CO2 and the atmospheric
transmission for the on-line backscattered signal caused by CO2 is large. Measurable range of CO2 measurement was
limited. A laser frequency offset locking system was installed into the laser system to improved measurable range of
CO2 measurement. Two single-frequency continuous wave lasers are used for the laser frequency offset locking. One
laser (center, λCenter) of the two continuous lasers is directly locked to the R30 absorption line center of CO2 and the other
(on-line, λOn) is frequency-shifted to λCenter laser. Although long-range CO2 measurement depends on the laser frequency offset, the installation of the laser frequency offset realized vertical CO2 measurement in a range of up to the