Preliminary Testing of a Water-Vapor Differential Absorption LIDAR (DIAL) Using a Widely Tunable Amplified Diode Laser Source

Abstract

Water vapor plays an enormous role in Earth's atmospheric dynamics through cloud formation, precipitation, and interactions with electromagnetic radiation, especially its absorption of longwave infrared radiation. Detailed data of water vapor distribution and flux and related feedback mechanisms are required to better understand and predict local weather, global climate, and the water cycle. One method of obtaining this data in the boundary layer with improved vertical resolution relative to passive remote sensors is with a Differential Absorption LIDAR (DIAL) utilizing a compact laser diode source. While small, low power DIAL systems do not typically have the resolution capabilities of larger LIDARs, DIAL systems can be built much smaller and more robust at less cost, and therefore may be a reasonable choice for a multi-point array or satellite-borne system. Montana State University, with the expertise of its laser source development group, is engaged in experiments leading to a water vapor DIAL system that utilizes a widely tunable amplified external cavity diode laser (ECDL) transmitter. This transmitter will have the ability to tune across a 17 nm spectrum near 830 nm, allowing it access to multiple water vapor absorption lines of varying strengths. Because of this wide tunability, the optimal absorption line for the DIAL technique in this region can be used based upon existing atmospheric conditions. This paper highlights the progress made in several areas at Montana State University (MSU) towards characterization, design, and construction of a water vapor DIAL using this widely tunable amplified ECDL transmitter.