Profiling Fiber-Optic Diode Laser Doppler Velocimeter for Deployment in Coastal Waters: Prototype Development. Phase 2.

摘要

A prototype profiling fiber-optic diode laser Doppler velocimeter (FODLDV) for flow measurement in coastal waters was developed, fabricated, and tested. The two-velocity-component FODLDV, a backscattered version of a field proven diode laser Doppler velocimeter (DLDV), consists of a fiber-optic probe and link, an optronic module, a digital fast Fourier transform (FFT) based signal processor, and a data acquisition and control system (DACS). The fiber-optic probe and link are mounted on a traverse that facilitates velocity profiling up to a maximum range of 3 m. The 1.6-cm diameter probe houses the collimating lenses attached to three single-mode polarizing preserving fibers, the focusing/receiving lenses, and a multimode fiber. The four 12-m-long optic fibers, protected in a water-tight armor cable, serve as the optical link between the probe, and the module; the single mode fibers transmit the frequency-shifted laser beams to the probe, and the multimode fiber transmits the backscattered light back to the photodetector. Command files allow all the operational parameters of the signal processor and the traverse to be modified on-the-fly. To operate the profiling FODLDV in an autonomous mode, a command file may be set up and executed to conduct an experimental sequence lasting for days, limited only by the capacity of the hard disk.