A Comparison Between High Spectral Resolution and Raman Lidars
| Edwin Eloranta | University of Wisconsin |
| David Turner | University of Wisconsin-Madison |
| John Goldsmith | Sandia National Laboratories |
Category: Instruments
Information on the vertical distribution of optical depth in clouds and aerosol layers is required for radiative transfer computations. It cannot be reliably obtained from standard backscatter lidar or radar measurements. Both high spectral resolution and Raman lidars use molecular backscatter profiles, which have been separated from cloud and aerosol scattering to make robust optical depth measurements. The high spectral resolution lidar (HSRL) separates molecular Rayleigh scattering based on the spectral broadening. This broadening occurs due to the Doppler shifts caused by the thermal motion of molecules, while the Raman system uses the frequency shifts due to vibrational Raman scattering for the separation. The Rayleigh scattering cross section is approximately 1000 times larger than the Raman cross section, which benefits the HSRL and allows high signal-to-noise ratio measurements with low power transmitters. However, by virtue of operating at an eye-safe wavelength, Raman lidars can use much higher power transmitters. This, combined with the use of large telescopes, helps to compensate for the smaller Raman cross section. In addition, they are technically simpler systems and they also provide water vapor profiles. These factors make the choice of technologies more difficult. This presentation will examine the tradeoffs that must be considered in selecting between a Raman and HSRL system by examining their relative performance in tropical and Arctic atmospheres.
This poster will be displayed at ARM Science Team Meeting.
