A Temperature and Water Vapor Scanning Raman Lidar for Observation of Land-Atmosphere Interaction

To understand the interaction and feedback between the terrestrial ecosystem and the atmosphere, rapid (every few seconds) and spatially resolved (every few meters) vertical measurements of temperature and water vapor concentration in the atmospheric boundary layer are highly desired. The Raman lidar technique applied in the solar blind region is a suitable approach for achieving the task: pure rotational Raman spectra of atmospheric nitrogen and oxygen molecules excited by laser radiation of 266-nm wavelength are used to measure the air temperature. Working in a solar blind region with no sky background noise gives an advantage of all day operation as well as an opportunity to use high field-of-view receiving telescopes that allows the operational range of the lidar starting from ten-fifteen meters. Multi-mirror facet telescope design of the lidar provides small dynamic range of the signals (less than three times within the range from 50 to 500 meters), and therefore allows nearly constant measurement accuracy within the whole operational range. A unique diffraction grating polychromator with capability of stray light suppression of 7-8 orders of magnitude provides sufficient spectral purity of the Raman signals even when working in clouds or in a dense haze condition. The polychromator of the lidar is designed to combine in one optical channel the light collected with four receiving telescopes, while using the same dispersion elements for all the telescopes. Equipped with elevation and azimuthal scanning drives the system is capable of 3D mapping of atmospheric parameters. Calibration and field-test experiments have demonstrated the capability of lidar to acquire temperature profiles with high spatial and temporal resolutions and reasonable accuracy.