Development of a Scanning Laser Velocimeter for Coastal and Marine Applications. Phase 1 Feasibility Investigation

摘要

The feasibility of developing a scanning laser velocimeter (LV/S) for flow measurements in coastal waters and the marine atmospheric boundary layer was investigated. The LV/S, based on a field-proven diode laser Doppler velocimeter (DLDV) for ocean deployment under ice floes, will be designed for backscatter operation. The Phase I investigation has led to the adaptation of a laser diode array rather than a single-element laser diode operating in a pulsed mode, as was originally proposed. At present, the coherence length and pulse width of pulsed laser diodes, which were the two major concerns of the Phase I work, are too short to be suitable as the light source of conventional LDVs. The availability of a high-power laser diode array (up to 5 W) allows operation of the laser diode in the continuous-wave (CW) mode, significantly reducing the potential complexity in the design of signal processors. The scanning diode laser array velocimeter (DLAV/S) will measure profiles of mean and fluctuating flow components as well as wind shear. For measurements in seawater, a diode-pumped YAG laser at 532 nm is a good alternative light source due primarily to its extremely low attenuation, compared to that of diode lasers at 800 nm. Because laser anemometry is also capable of measuring particle size distribution and number density, simultaneous measurements of particle speed, size distribution, and number density may be made with the LV/S. A scanning optical system will be designed for scanning the focal volume, with ranges up to 3 m. During Phase II, test models will be designed, assembled, and tested, leading to the development of a prototype device for field deployment.