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Non-Contact Velocity Measurement on Simulated River Surfaces with Coherent Doppler Lidar

Preliminary results of Doppler Lidar technology validated for flow measurement on simulated river surfaces. Investigates velocity profiles, surface topography, and discharge using Coherent Doppler Wind Lidar. Collaboration with USGS and U. Washington planned.

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Non-Contact Velocity Measurement on Simulated River Surfaces with Coherent Doppler Lidar

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  1. Non-Contact Velocity Measurementson Simulated River Surfaces Using Coherent Doppler LidarPreliminary Results Prepared by J. Rothermel* and S.C. Johnson (NASA MSFC) P.A. Kromis (Computer Science Corporation) Earth Science Department NASA Marshall Space Flight Center Updated by D. Bowdle** (University of Alabama in Huntsville) *jeffry.rothermel@msfc.nasa.gov **David.Bowdle@msfc.nasa.gov

  2. MSFC Coherent Doppler Wind Lidar • Initiated April 1999 • Purpose: CDWL technology validation Atmospheric properties research Space CDWL concepts investigation CDWL targets research Student Instruction • Location: MSFC Building 4467 GSFC van (proposed) Van or trailer (future) Aircraft (future) • Initial components: Transceiver, 50 mJ, 6.6 Hz, 2.017 microns, FL pumped 10 cm telescope from Schwartz Electro-Optics, Inc. Full hemispheric scanner (Bldg. 4467) Data acquisition & processing

  3. Long-term Objective Streamflow Measurement with Doppler Lidar • Complement proposed microwave radar measurements • Relationship among surface velocity profile, bottom topography, and discharge • Based on phased approach • Controlled experimental conditions (initial phase) • Collaborations with USGS, U. Washington (later phases) Doppler lidar is only technique that can directly measure the influence of near-surface winds

  4. Background Water surface velocity measurements depend on: • Lidar wavelength • Surface roughness • Incidence (or nadir) angle • Turbidity • Surface contaminants (e.g., foam) • Depth of penetration (of order millimeters at 2 micron) • Near-surface wind velocity

  5. (Very) Preliminary Experiment at MSFC Target ~350 m range Target Lidar Lidar

  6. Water Slide Geometry Slit Water Flow Lidar Beam Water slide Nadir Angle

  7. Experiment Parameters • MSFC Doppler lidar, 6.6 Hz, 2.017 m • Velocities toward lidar are negative (-) • Water discharge nozzles: weirgate on new waterslide • Water slide surface composition: plexiglass • Lidar beam footprint: ~10 cm • Discharge depth: several mm (variable) • Nadir angles at target: 30, 60 deg • Integration: 20 pulses • Range gate, velocity plots: 210 m, centered on target • Range gate, range plots: 38.4 meters • Range to target: ~350 meters • Minimum range: ~150 meters • Number of good range gates in air near target: ~5

  8. Conclusions and Plans Conclusions • Velocity standard deviation for hard target is ~0.1 m/s. • Velocity decreases slowly as reservoir empties, allows integration • Surface tension effects from untreated plexiglass slide surface create • flow channeling, with variable water layer thickness • non-riverine water surface microstructure • Sanding the plexiglass surface reduces surface tension effects • virtually eliminates flow channeling • nearly mirror smooth water surfaces Plans • Resume lidar operations (after minor repairs) • Test runs with variable flow velocity and layer thickness • Test runs with controlled surface condition

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