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B. Gentry/GSFCSLWG 06/29/05 Scaling Ground-Based Molecular Direct Detection Doppler Lidar Measurements to Space Using Wind Profile Measurements from GLOW B. Gentry, J. Comer, M. McGill NASA / GSFC
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B. Gentry/GSFCSLWG 06/29/05 Q: How can we use ground based measurements to refine and validate future space based lidar system designs? 1)Validate the instrument performance behaves predictably versus measurable quantity (signal photocounts; signal to noise) under a variety of conditions. 2)Establish reference system designs to examine impact of performance trades (e.g. spatial and temporal averaging schemes) or engineering trades 3)Scaling of ground based system performance to equivalent space- based system reveals where improvements are required and provides direction for technology and instrument system development programs 4)Scaling also provides a sanity check for space based designs
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B. Gentry/GSFCSLWG 06/29/05 Mobile Lidar Optical Layout
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B. Gentry/GSFCSLWG 06/29/05 Double Edge Etalon Channels
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B. Gentry/GSFCSLWG 06/29/05 Wind Measurement and Error Analysis Case study: Field measurements of wind speed and direction in stable atmospheric conditions HARGLO-2, November 16, 2001 Algorithms used to determine wind speed and direction Error analysis based on shot noise limited error
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B. Gentry/GSFCSLWG 06/29/05
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B. Gentry/GSFCSLWG 06/29/05 1 2 3 4 5
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B. Gentry/GSFCSLWG 06/29/05 Combined Molecular Sensitivity vs. T and v T= 150K to 350K, v = 0 to 100 m/s
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B. Gentry/GSFCSLWG 06/29/05
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B. Gentry/GSFCSLWG 06/29/05
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B. Gentry/GSFCSLWG 06/29/05
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B. Gentry/GSFCSLWG 06/29/05 Q: How can we use ground based measurements to refine and validate future space based lidar system designs? 1)Validate the instrument performance behaves predictably versus measurable quantity (signal photocounts; signal to noise). 2)Establish reference system designs to examine impact of performance trades (e.g. spatial and temporal averaging schemes) or engineering trades 3)Scaling of ground based system performance to equivalent space- based system reveals where improvements are required and provide direction for technology and instrument system development programs 4)Scaling also provides a sanity check for space based designs
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B. Gentry/GSFCSLWG 06/29/05 N S = number of laser shots atm ( )=1 way atmos transmission A= telescope area a ( )= aerosol backscatter E= laser pulse energy m ( )=molecular backscatter = detection efficiencyR= range to sample volume opt = optical efficiency R= range resolution h = photon energy Direct Detection Doppler Lidar SNR N S EA opt atm 2 ( ) [ a ( )+ m ( )] R h R 2 SNR=sqrt
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B. Gentry/GSFCSLWG 06/29/05 Wavelength354.7 nm Telescope/Scanner Area0.116 m 2 Laser Linewidth (FWHH)80 MHz Laser Energy/Pulse 25 mJ @ 50pps Etalon FSR 12 GHz Etalon FWHH1.7 GHz Edge Channel Separation5.1 GHz Locking Channel Separation 1.7 GHz Interference filter BW (FWHH)150 pm PMT Quantum Efficiency22% GLOW Lidar System Parameters -- June 21, 2005
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B. Gentry/GSFCSLWG 06/29/05 GLOW System Efficiencies (6/21/2005) Energy Monitor Channel Edge Channels Telescope/Scanner0.26 FO Attenuation0.82 FO Coupling0.75* Interference Filter0.42 Receiver Optics0.930.90 Optical efficiency (w/o BS and Etalon) 0.0830.080 BS0.0560.41 Etalon Trans (Mol. Edge)--0.154 PMT PD0.22 Total efficiency0.0010.0011 * Estimated value. Includes Fresnel losses, boresight and alignment losses.
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B. Gentry/GSFCSLWG 06/29/05 Comparison of Measured and Simulated Signals June 21, 2005
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B. Gentry/GSFCSLWG 06/29/05 GLOW LOS Error z=0.5 km; t=1 min
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B. Gentry/GSFCSLWG 06/29/05 Scaling GLOW to 400 km at z=10km GroundSpaceScaling factor parameters Integration Time (s)60106 z/cos (km) 0.7071.410.5 Laser Power J/s1.25 W (50 Hz, 0.025 J) 30W (100 Hz, 0.3 J) 0.0417 Telescope area (m 2 )0.1160.750.155 Atmospheric transmission0.20.950.21 Detector quantum efficiency0.220.30.73 Optics transmission0.060.300.2 Range to Target Volume (km)14.14551.61522 Scale factor product = 0.9
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B. Gentry/GSFCSLWG 06/29/05 Edge Signals from 400 km
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B. Gentry/GSFCSLWG 06/29/05 Simulated LOS Error from 400 km z=1 km; t=10 sec
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B. Gentry/GSFCSLWG 06/29/05 Summary Ground based lidar measurements provide important insight into performance of future air and space based lidar systems –Measurements provide experimental validation of atmospheric and instrument models –Inversion of lidar measurement performance can be scaled to space for a single altitude/signal level –This information can be used to guide technology development and explore sysetem trades for future designs
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B. Gentry/GSFCSLWG 06/29/05
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B. Gentry/GSFCSLWG 06/29/05
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B. Gentry/GSFCSLWG 06/29/05 Incident Photon Count Rate
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B. Gentry/GSFCSLWG 06/29/05 2-way atmospheric transmission
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B. Gentry/GSFCSLWG 06/29/05
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B. Gentry/GSFCSLWG 06/29/05
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