Date: Monday, January 6, 2014
Time: 8:00 am
Location: PHYS 401
A New Differential Absorption Lidar Using Raman Cells to Measure Subhourly Variation of Tropospheric Ozone Profiles in the Baltimore - Washington D.C. region
This proposal will detail the theory and background necessary for the ground based tropospheric ozone Differential Absorption Lidar (DIAL) system at the NASA Goddard Space Flight Center (Greenbelt, MD 38.99° N, 76.84° W, 57 meters ASL), with initial results from 500 m to 10 km in Summer 2013. Current atmospheric satellites cannot peer through the optically thick stratospheric ozone layer to remotely sense boundary layer tropospheric ozone. In order to monitor this lower ozone more effectively, NASA has funded the ground based Tropospheric Ozone Lidar Network (TOLNET) which currently consists of five stations across the US. The Goddard instrument is based on the Differential Absorption Lidar (DIAL) technique, which transmits three wavelengths, 266, 289 and 299 nm. Ozone is absorbed more strongly at 266 nm and 289 nm than at 299 nm. The DIAL technique exploits this difference between the returned backscatter signals to obtain the ozone number density as a function of altitude. The transmitted wavelengths are generated by focusing the output of a quadrupled Nd:YAG laser beam (266 nm) into a pair of Raman Cells, filled with high pressure Hydrogen and Deuterium. Stimulated Raman Scattering within the focus shifts the pump wavelength and the first Stokes shift in each cell produces the required wavelengths. With the knowledge of the ozone absorption coefficient at these two wavelengths, the range resolved number density can then be derived. A interesting scientific validation data set will be examined, which yields accurate initial results. There are currently surface ozone measurements hourly and ozonesonde launches occasionally, but this system will be the first to make continuous routine ozone profile measurements in the Washington, DC - Baltimore area.