Knowledge Bank

DIAL lidar for water vapor and temperature remote sensing in the eye safe atmospheric window regions has been receiving much interest. Such systems rely on accurate spectral line characterization. Typically the HITRAN data base on atmospheric spectral lines is used. However, the database is incomplete and not sufficiently accurate. A series of transmittance measurements are made on water vapor and carbon dioxide to verify and improve the HITRAN data base in $2\mu m$ spectral $region1$. 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 on pure $H2O$ at various pressures, $N2$ broadened $H2O$ and $N2-O2$ broadened $H2O$ are collected at room temperature. Also, measurements on pure $CO2$ at various pressures and $N2$ broadened $CO2$ are collected at room temperature. Data analysis is performed on lines that are accessible by lasers. The measured spectrum is converted to the absorption coefficient and is fitted to a synthetic spectrum to determine the spectral line parameters. This includes the pressure shift, halfwidth and line strength. Water vapor exhibits a strong pressure shift effect. Oxygen broadening is observed to be significantly less than that due to nitrogen. Some lines show good agreement (within a few percent) with the HITRAN database, other lines disagree by more than $\pm 10$. Thus care must be exercised in applying the HITRAN data based to DLAL lidar applications. The pressure shift, self-halfwidth and oxygen-broadened halfwidth are not available on the HITRAN database.