This study developed rotational Raman lidar system for atmospheric temperature measurement. Measuring temperature using lidar is taken only in the night time because of strong elastic scattering signal caused by the effect of the sunlight background signal and a small difference of 0.5 to 1.1nm in wavelength between rotational Raman signal and elastic scattering signal.
To decrease the background signal from sunlight, lidar system installed a 0.5nm FWHM narrow band pass filter with a high rejection rate of 10-6 and designed using a 1650groove/mm grating, a 400μm pinhole and a fiber bundle.
Generally, other research teams use 354.70nm wavelength to find atmospheric temperature from the ratio of signals by selecting 353.35nm and 354.20nm wavelength which are proportion and inverse proportion to the temperature change. In this study, the selected wavelengths for the calculation of the temperature are 353.1nm and 353.9nm and those are the wavelengths for elastic scattering signal and rotational Raman signal. Atmospheric temperature was calculated by the ratio of 353.1nm Raman signal to 353.9nm Raman signal.
During the strongest sunlight time of 13:00 ∼ 14:00 PM measurement 1,600 photons were measured as a background signal due to the bright sunlight. The separation of elastic scattering signal and the rotational Raman signals also measured and confirmed in a cloudy day.
The horizontal temperature profile measured in our lidar system was compared with KMA (Korea Meteorological Administration) data and it was well matched with theoretical calculations and come out in agreement within a margin of error ±1℃. We have found that our temperature profile has a good correlation with KMA data within our theoretically expected variance. And we have used these calibration values in obtaining a vertical temperature distribution.
To check the accuracy of our system, we also have compared our vertical temperature data with US standard atmospheric temperature profile. It was found that there is some error up to 1,300m, but, over 1,300m the mean values tend to be in good agreement accord with the standard temperature data. Simultaneous measurement of our lidar and Radiosonde in January 6, 2012 in Pohang Regional Meteorological Office show that the measured temperature profile is in good agreement in the range of 2,000m ∼ 5,000m.