Characterization of optical extinction profiles using Raman lidar techniques
Document ID: 135
O'Brien, Michael D.
Philbrick, C. Russell
The Pennsylvania State University, Department of Electrical Engineering, University Park, PA, U.S.A.
Abstract
The presence of aerosol particles and cloud droplets in the atmosphere strongly affects the propagation of light through the atmosphere. These particles have an important impact on the Earth's climate and the operation of electro-optical sensors. A useful tool for measuring optical extinction due to aerosols is a Raman lidar. Raman lidars also have the capability to measure atmospheric temperature and humidity. The lidars we have at Penn State also have the capability to measure ozone in the lower troposphere. This profile can then be used to determine the extinction due to ozone absorption. The present lidar system provides extinction measurements at UV and visible wavelengths. The technique has been verified over a horizontal path with independent measurements of the particle size distribution and provides measurements with a high degree of temporal resolution.
The current lidar system employs Raman scatter from a ND:YAG laser beam from the 2nd, 3rd, and 4th harmonics at 532, 355, and 266 nm to obtain the profiles of optical extinction. The measurements have been made using the molecular nitrogen profiles at 607, 387, and 285 nm, which are the first Stokes vibrational Raman shifts from the ND:YAG laser. The rotational Raman scatter at 530 nm has also been used to obtain optical extinction profiles. This paper will begin with a description of the two Raman lidars used to acquire the data to be presented. Next, the details of our analysis will be discussed. Then, the capabilities of the system will be illustrated with several examples of data taken during two field campaigns.