NonContact Velocity Measurements on Simulated River Surfaces Using Coherent Doppler Lidar Preliminar

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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_at_msfc.nasa.gov David.Bowdle_at_msf
c.nasa.gov
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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

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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
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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

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(Very) Preliminary Experiment at MSFC
Target
350 m range
Target
Lidar
Lidar
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Water Slide Geometry
Slit
Water Flow
Lidar Beam
Water slide
Nadir Angle
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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

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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