Daytime temperature profiling of UV rotational Raman lidar using a multispectral detector

Abstract:

Temperature profiling in the atmospheric boundary layer is essential in meteorological studies for understanding atmospheric processes. In this study, we developed a temperature lidar with a multispectral detector to construct a system that is compact, robust, and easy to align for the detection of rotational Raman signals. The multispectral lidar detector, which is based on a linear array multianode photomultiplier tube assembly, allows simultaneous detection of multiple spectrometer wavelengths. We can select a suitable observation wavelength using motorized accessory controls in spectroscopy and scanning software. The developed system enables the acquisition of shapes of rotational Raman spectra. Atmospheric temperature can be estimated by direct fitting of the observed lidar signals to the acquired theoretical shapes that exhibit different dependencies on temperature.

In the laser wavelength of the Raman lidar system, the ultraviolet (UV) wavelength has advantages over the visible wavelength because the rotational Raman backscatter coefficient is proportional to the minus fourth power of wavelength. Moreover, UV lidars achieve better daytime performances than visible systems because of reduced sky background. Here, we have developed two Raman lidar systems, which are equipped with lasers at wavelengths of 266 nm and355 nm. In the multispectral detector, the rotational Raman lidar signal has several uncertainties that cause significant errors during temperature estimation. For example, the light detection efficiency is not uniform for each channel in the multispectral detector. Here, we demonstrate the calibration techniques of the developed system and report the preliminary results of temperature observations in the planetary boundary layer at the middle and upper (MU) radar observatory (34.8°N, 136.1°E) in Shigaraki, Japan.