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WATER VAPOUR RAMAN LIDARS IN THE UTLS: Where Are We Now? or “The JPL-Table Mountain Experience”

WATER VAPOUR RAMAN LIDARS IN THE UTLS: Where Are We Now? or “The JPL-Table Mountain Experience”. Thierry Leblanc. NASA Jet Propulsion Laboratory California Institute of Technology Wrightwood, CA USA. Lidar Technique: Brief Overview.

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WATER VAPOUR RAMAN LIDARS IN THE UTLS: Where Are We Now? or “The JPL-Table Mountain Experience”

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  1. WATER VAPOUR RAMAN LIDARS IN THE UTLS: Where Are We Now? or “The JPL-Table Mountain Experience” Thierry Leblanc NASA Jet Propulsion Laboratory California Institute of Technology Wrightwood, CA USA

  2. Lidar Technique: Brief Overview Raman-backscatter Lidar Equationfor any atmospheric molecule M: AL dz sM(lR) NM(z) SM(z) = PL t(lL,lR,z) hM eM(lR) OM(z) (z - zL)2

  3. Lidar Technique: Brief Overview Raman-backscatter Lidar Equationfor any atmospheric molecule M: AL dz sM(lR) NM(z) SM(z) = PL t(lL,lR,z) hM eM(lR) OM(z) (z - zL)2 Signal collectedin Raman channelfor altitude z…

  4. Lidar Technique: Brief Overview Raman-backscatter Lidar Equationfor any atmospheric molecule M: AL dz sM(lR) NM(z) SM(z) = PL t(lL,lR,z) hM eM(lR) OM(z) (z - zL)2 Signal collectedin Raman channelfor altitude z… …is proportional to the numberof photons emitted by laser…

  5. Lidar Technique: Brief Overview Raman-backscatter Lidar Equationfor any atmospheric molecule M: AL dz sM(lR) NM(z) SM(z) = PLt(lL,lR,z) hM eM(lR) OM(z) (z - zL)2 Signal collectedin Raman channelfor altitude z… …is proportional to the numberof photons emitted by laser… …and after a fewtypical lidar corrections…

  6. Lidar Technique: Brief Overview Raman-backscatter Lidar Equationfor any atmospheric molecule M: AL dz sM(lR) NM(z) SM(z) = PL t(lL,lR,z) hM eM(lR) OM(z) (z - zL)2 Signal collectedin Raman channelfor altitude z… …to the number ofscattering moleculesat altitude z …is proportional to the numberof photons emitted by laser… …and after a fewtypical lidar corrections…

  7. Lidar Technique: Bref Overview Raman-backscatter Lidar Equationfor any atmospheric molecule M: AL dz sM(lR) NM(z) SM(z) = PL t(lL,lR,z) hM eM(lR) OM(z) (z - zL)2 This equation applies similarly to water vapour (our target)and Nitrogen (a well-mixed “reference” gas) …so that the ratio of the signal collected in the H2O channel to thatcollected in the N2 Raman channel is proportional to H2O mixing ratio q: SH2O(z) NH2O(z) R(z) = = k = k q(z) SN2(z) NN2(z) sH2OhH2O eH2O OH2O with k = Dt sN2hN2 eN2 ON2 The determination of k is referred to as the lidar calibration

  8. Calibration: Two Approaches 1. Independent, also known as “absolute” or “experimental”Calculate each individual term in lidar ratio equationNeed calibrated lamp, manufacturer specs of all optics and electronics, etc…Difficult to achieve, especially on a routine basisEstimated uncertainty: 7-20% 2. External, also known as “absolute” or “a priori”Estimate all the altitude-dependent terms in lidar ratio equation,then normalize to a well-known external measurement,for example, radiosonde in the lower troposphere, or GPS total columEasier to achieve than method 1, but not independent from other instrumentsEstimated uncertainty (radiosonde): 3-15%Estimated uncertainty (GPS): 7-15% Hybrid Method: A combination of the two methods above1. Perform external calibration during (yearly) campaigns2. Monitor lidar receiver stability between campaigns using lampNot more accurate than external calibration, but saves money and timeby avoiding systematic routine radiosonde launches  Recommended (but not mandatory) practice by NDACC

  9. Calibration:One example (radiosonde) Radiosonde in blue

  10. Calibration:One example (radiosonde) Lidar in red Best fit to radiosonde Calibrated

  11. Why are H2O Lidar MeasurementsChallenging in the UTLS? 1. Vibrational Raman scattering is 1000 times weaker than Rayleigh scattering 2. Water Vapor mixing ratio drops down to less than 10 ppmv in the UTLS As a result: H2O signal is 109 times weaker than Rayleigh signal in UTLSand therefore very challenging to detect…

  12. Resulting in a Long and Winding Road… 2002:NDACC considers Raman WV lidar as new NDACC instrument April 2005: TMF WV Raman Lidar First Light June 2005 - Present: Routine measurements 2h/night, 3-4 nights per week Oct 2006: Validation campaign MOHAVE  Fluorescence Detected! Oct 2007: Validation campaign MOHAVE-II Fall 2008: H2O Raman lidar becomes an official NDACC instrument Summer 2009: Six H2O Raman lidars provisionally accepted (need validation) Fall 2009: TMF H2O Raman lidar Validated

  13. Resulting in a Long and Winding Road… April 2005: TMF WV Raman Lidar First Light  June 2005 – Present: Routine measurements 2h/night, 3-4 nights per week Oct 2006: Validation campaign MOHAVE  Fluorescence Detected! Oct 2007: Validation campaign MOHAVE-II Fall 2008: H2O Raman lidar becomes an official NDACC instrument Summer 2009: Six H2O Raman lidars provisionally accepted (need validation) Fall 2009: TMF H2O Raman lidar Validated

  14. Early Results: 2005-2006 RS92 (corrected) vs. LidarComparison shows: 2005-2007 Climatology (average of 202 profiles)  Lidar Very Wet or RS92 Very Dryor Both!

  15. A Long and Winding Road… April 2005: TMF WV Raman Lidar First Light June 2005 - Present: Routine measurements 2h/night, 3-4 nights per week Oct 2006: Validation campaign MOHAVE  Fluorescence Detected!  Oct 2007: Validation campaign MOHAVE-II Fall 2008: H2O Raman lidar becomes an official NDACC instrument Summer 2009: Six H2O Raman lidars provisionally accepted (need validation) Fall 2009: TMF H2O Raman lidar Validated

  16. MOHAVE Campaign (Oct 2006):Fluorescence Detected Strong Rayleigh signal (355 nm) induces fluorescence in lidar receiverComparison below shows lidar vs. CFH mean profileswhen 355 nm blocked at the receiver’s entrance (right), andwhen 355 nm is not blocked (left)  New anti-fluorescent optics were ordered, custom-madeand installed on the TMF lidar during summer 2007

  17. Since July 2007: Fluorescence is gone RS92 (corrected) vs. LidarComparison shows: 2007-2009 by Season (154 profiles) The corrected RS92 is still too dry: Not a lidar problem anymore

  18. A Long and Winding Road… April 2005: TMF WV Raman Lidar First Light June 2005 - Present: Routine measurements 2h/night, 3-4 nights per week Oct 2006: Validation campaign MOHAVE  Fluorescence Detected! Oct 2007: Validation campaign MOHAVE-II Fall 2008: H2O Raman lidar becomes an official NDACC instrument  Summer 2009: Six H2O Raman lidars provisionally accepted (need validation) Fall 2009: TMF H2O Raman lidar Validated

  19. (as of 2008) Prior to 2009:No Water Vapor Lidars in NDACC

  20. (as of 2009) Since 2009:Six Water Vapor Lidars provisionally in NDACC “Provisionally” because (more) validation is required

  21. A Long and Winding Road… April 2005: TMF WV Raman Lidar First Light June 2005 - Present: Routine measurements 2h/night, 3-4 nights per week Oct 2006: Validation campaign MOHAVE  Fluorescence Detected! Oct 2007: Validation campaign MOHAVE-II Fall 2008: H2O Raman lidar becomes an official NDACC instrument Summer 2009: Six H2O Raman lidars provisionally accepted (need validation)  Fall 2009: MOHAVE-2009 Campaign TMF H2O Raman Lidar Validated

  22. October 2009:TMF Lidar Profiles Fully Validated Latest (optimized) receiver configuration since July 2009Comparison below shows lidar vs. CFH mean profiles during MOHAVE-2009Below 14 km: Average of 12 one-hour-integrated profiles coincident with balloonAbove 14 km: Average of 8 full nights with coincident CFH flights

  23. Conclusions and Perspectives TMF Water Vapor Lidar Program:Started in 2005 Period 2005-2007:Plagued with fluorescence(no satisfactory results above 12 km) Early Analysis (2007-2009):Pronounced Annual Cycle (summer max) Re-Analysis Back to 2007:Expected to be Available Late 2011

  24. OZONE TEMPERATURE WATER VAPOR ? Table Mountain 15-25 km water vapor anomaly (%) 2010 2020 2030 from Steinbrecht et al., 2008 Back to NDACC (long-term) Context TMF = Significant NDACC past and presentcontribution to Ozone and Temperature Trends… We hope for a similar contributionfor Water Vapor… in 2030! THANK YOU ! Please visit JPL-TMF lidar website:http://tmf-lidar.jpl.nasa.gov/

  25. Backup Slides

  26. Tropopause All 2005-2009 RS92 Temperature Profiles:WMO TP in BlueCold-Point TP in red Text Text Typically Two Regimes:Well-defined Tropical-Type Unique Cold-Point TP in SummerSeparate WMO and Cold-Point TP Typical of mid-lat. in Winter

  27. What is the Hybrid Calibration Method? 1. A calibrated laboratory lamp is permanently mounted above the lidar’s primary telescope mirror 2. Routine 5-min lamp data acquisition is performed just before and after the normal data acquisition 3. Once a year, absolute calibration campaigns are organized (lamp runs still included) 4. The “transfer function”, which is the quotient of the lamp ratio by the absolute calibration constant, is monitored with time, and should remain constant if the lidar receiver remains stable

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