Preliminary Measurements with CODI: an Automated Compact Water Vapor DIAL

1. Preliminary Measurements with CODI:an Automated Compact Water Vapor DIAL Janet Machol, NOAA ETL / CIRES Need for a New Lidar Measurements Continuous water vapor profiles would help improve weather forecasts and climate studies. Currently, routine water vapor profiles are taken with twice-daily radiosondes. Lidars can provide continuous profiles, but to date, most water vapor lidars have been large, expensive and complex instruments. We built an eye-safe automated DIfferential Absorption Lidar (DIAL) to profile water vapor in the lower troposphere. CODI (COmpact DIAL) was designed to be a prototype of a low-cost lidar which can be duplicated for multiple deployments. The lidars could be placed adjacent to wind profilers to measure moisture transport. Water vapor lidar deployed at CART site during IHOP. The first field test of the system was at the SGP ARM CART site in Oklahoma during the IHOP experiment. Failure of the air conditioners precluded getting good data at IHOP. Here we present nighttime profiles taken in Boulder compared with both ground-based in situ sensors and with a radiosonde. Design CODI is a low power infrared DIAL based on diode lasers and photon counting detection. A DIAL measures water vapor by detecting the returns from laser pulses emitted at two wavelengths, on and off of a water vapor absorption line. The instrument is in a weather-proof housing and can run unattended for days. The lidar automatically switches and locks the DIAL wavelengths and does periodic adjustments of the optics. The seed laser is a distributed feedback (DFB) laser amplified by a flared diode amplifier. Typical nighttime traces use 30-minute and 180-m averages Comparison of vertical DIAL measurement with a radiosonde. On- and off-line atmospheric returns. Results These Boulder measurements validate the lidar, but also demonstrate the need for several improvements on the instrument: the addition of a near-field channel to obtain measurements below 500 m, a higher-power laser to permit better resolution and daytime measurements, and improved climate control in extreme conditions. Horizontal water vapor profiles. Specifications Acknowledgements Special thanks to Mike Hardesty, Tom Ayers, Karl Schwenz, Keith Koenig, Mike Krainak, Jim Abshire, Leo Hollberg, Hector Bravo, Dave White, Christoph Senff, and Scott Sandberg. Funding was provided by NOAA ETL, NOAA OGP, NCAR ATD, and NASA GSFC. Comparison of horizontal DIAL measurements at 1000-m range gate with in situ sensors. Boulder map at right shows sensor locations.