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Prepared by J. Rothermel* and S.C. Johnson (NASA MSFC) P.A. Kromis (Computer Science Corporation)

Non-Contact Velocity Measurements on Simulated River Surfaces Using Coherent Doppler Lidar Preliminary 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

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Prepared by J. Rothermel* and S.C. Johnson (NASA MSFC) P.A. Kromis (Computer Science Corporation)

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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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