DEVELOPMENT OF A SCANNING PULSED DIODE LASER DOPPLER VELOCIMETER FOR FLOW MEASUREMENTS IN COASTAL AND MARINE ENVIRONMENTS

A SCANNING, PULSED DIODE LASER DOPPLER VELOCIMETER (DLDV/SP) WILL BE DEVELOPED FOR FLOW MEASUREMENTS IN AIR AND WATER, PARTICULARY COASTAL WATERS AND THE MARINE ATMOSPHERIC BOUNDARY LAYER. THE DLDV/SP, BASED ON A FIELD-PROVEN DLDV FOR OCEAN DEPLOYMENT UNDER ICE FLOWS, WILL BE DESIGNED FOR ON-AXIS BACKSCATTER OPERATION. IN A PULSED MODE, THE DIODE LASER WILL GENERATE INSTANTANEOUS LASER POWER IN THE TENS OF WATTS, WHICH IS NECESSARY FOR THE SCANNING, BACKSCATTER OPERATION. TWO CRITICAL ISSUES THAT MUST BE RESOLVED ARE THE EXTREMELY SHORT PULSE WIDTH (200 TO 500 NS) AND THE RELATIVELY LARGE SPECTRAL WIDTH (ABOUT 3.5 NM). TO RESOLVE THESE ISSUES, WE PROPOSE, RESPECTIVELY, THE INCORPORATION OF AN OPTICAL MODULATION SCHEME TO CREATE A "RUNNING" FRINGE PATTERN AND THE IMPLEMENTATION OF OPTICAL FILTERING OR AN ETALON. THE DLDV/SP WILL MEASURE PROFILES OF MEAN AND FLUCTUATING FLOW COMPONENTS AS WELL AS SHEAR FLOW. BECAUSE LASER ANEMOMETRY IS ALSO CAPABLE OF MEASURING PARTICLE SIZE DISTRIBUTION AND NUMBER DENSITY, SIMULTANEOUS MEASUREMENTS OF PARTICLE SPEED AND SIZE DISTRIBUTION AND NUMBER DENSITY MAY BE MADE WITH THE DLDV/SP. A ZOOM OPTICAL SYSTEM WILL BE DESIGNED FOR SCANNING THE FOCAL VOLUME, WITH RANGES ON THE ORDER OF 10 M IN AIR AND 1 M IN WATER. DURING PHASE I, A TEST MODEL WILL BE DESIGNED, ASSEMBLED, AND TESTED TO DETERMINE THE FEASIBILITY OF THE PROPOSED DEVELOPMENT.