Characterization of candidate DIAL lidar water-vapor and carbon dioxide absorption lines in the 2-um region

Abstract

DIAL lidar for water-vapor and temperature remote sensing in the eye-safe two micron region has been receiving much interest. Such systems rely on accurate spectral line characterization. Typically spectral line properties are taken from the HITRAN database. A series of transmittance measurements are made to complete and improve the HITRAN database in this important spectral region. A 3-meter base-path White cell attached to a BOMEM DA3.02 is used for the transmittance measurements. The White cell is set to a path length of 216 meters for all experiments. Measurements of pure water-vapor, nitrogen broadened water-vapor, pure carbon dioxide, and nitrogen broadened carbon dioxide are collected at room temperature. Data analysis is performed on water-vapor lines that are relatively temperature insensitive and carbon dioxide lines that are relatively temperature sensitive over the range of typical atmospheric temperatures. The measured spectrum is converted to the absorption coefficient and is nonlinear least squares fitted to determine the spectral line parameters. Some lines show good agreement (within a few percent) with the HITRAN database, other lines disagree by more than +/- 10%. Thus care must be exercised in applying the HITRAN database to DIAL lidar applications. New parameters are obtained that are not available on the current 1992 HITRAN database, such as the self width and pressure shift.