GEWEX/GlobVapour Workshop, Mar 8-10, 2011, ESRIN, Frascati, Italy 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

GEWEX/GlobVapour Workshop, Mar 8-10, 2011, ESRIN, Frascati, Italy Lidar Technique: Brief Overview Raman-backscatter Lidar Equation for any atmospheric molecule M: S M (z) = P L t( L, R,z)  M  M ( R ) O M (z) A L  z (z - z L ) 2  M ( R ) N M (z)

GEWEX/GlobVapour Workshop, Mar 8-10, 2011, ESRIN, Frascati, Italy Lidar Technique: Brief Overview Raman-backscatter Lidar Equation for any atmospheric molecule M: S M (z) = P L t( L, R,z)  M  M ( R ) O M (z) A L  z (z - z L ) 2  M ( R ) N M (z) Signal collected in Raman channel for altitude z…

GEWEX/GlobVapour Workshop, Mar 8-10, 2011, ESRIN, Frascati, Italy Lidar Technique: Brief Overview Raman-backscatter Lidar Equation for any atmospheric molecule M: S M (z) = P L t( L, R,z)  M  M ( R ) O M (z) A L  z (z - z L ) 2 …is proportional to the number of photons emitted by laser…  M ( R ) N M (z) Signal collected in Raman channel for altitude z…

GEWEX/GlobVapour Workshop, Mar 8-10, 2011, ESRIN, Frascati, Italy Lidar Technique: Brief Overview Raman-backscatter Lidar Equation for any atmospheric molecule M: S M (z) = P L t( L, R,z)  M  M ( R ) O M (z) A L  z (z - z L ) 2 …is proportional to the number of photons emitted by laser… …and after a few typical lidar corrections…  M ( R ) N M (z) Signal collected in Raman channel for altitude z…

GEWEX/GlobVapour Workshop, Mar 8-10, 2011, ESRIN, Frascati, Italy Lidar Technique: Brief Overview Raman-backscatter Lidar Equation for any atmospheric molecule M: S M (z) = P L t( L, R,z)  M  M ( R ) O M (z) A L  z (z - z L ) 2 Signal collected in Raman channel for altitude z… …to the number of scattering molecules at altitude z …is proportional to the number of photons emitted by laser… …and after a few typical lidar corrections…  M ( R ) N M (z)

GEWEX/GlobVapour Workshop, Mar 8-10, 2011, ESRIN, Frascati, Italy Lidar Technique: Bref Overview This equation applies similarly to water vapour (our target) and Nitrogen (a well-mixed “reference” gas) Raman-backscatter Lidar Equation for any atmospheric molecule M: S M (z) = P L t( L, R,z)  M  M ( R ) O M (z) A L  z (z - z L ) 2  M ( R ) N M (z) R(z) = S H2O (z) S N2 (z) = k q(z)  H2O  H2O  H2O O H2O  N2  N2  N2 O N2 with k =  t The determination of k is referred to as the lidar calibration N H2O (z) N N2 (z) = k …so that the ratio of the signal collected in the H2O channel to that collected in the N2 Raman channel is proportional to H2O mixing ratio q:

GEWEX/GlobVapour Workshop, Mar 8-10, 2011, ESRIN, Frascati, Italy Calibration: Two Approaches 1. Independent, also known as “absolute” or “experimental” Calculate each individual term in lidar ratio equation Need calibrated lamp, manufacturer specs of all optics and electronics, etc… Difficult to achieve, especially on a routine basis Estimated 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 colum Easier to achieve than method 1, but not independent from other instruments Estimated uncertainty (radiosonde): 3-15% Estimated uncertainty (GPS): 7-15% Hybrid Method: A combination of the two methods above 1. Perform external calibration during (yearly) campaigns 2. Monitor lidar receiver stability between campaigns using lamp Not more accurate than external calibration, but saves money and time by avoiding systematic routine radiosonde launches  Recommended (but not mandatory) practice by NDACC

GEWEX/GlobVapour Workshop, Mar 8-10, 2011, ESRIN, Frascati, Italy Radiosonde in blue Calibration: One example (radiosonde)

GEWEX/GlobVapour Workshop, Mar 8-10, 2011, ESRIN, Frascati, Italy Calibration: One example (radiosonde) Lidar in red Best fit to radiosonde  Calibrated

GEWEX/GlobVapour Workshop, Mar 8-10, 2011, ESRIN, Frascati, Italy 1. Vibrational Raman scattering is 1000 times weaker than Rayleigh scattering Why are H2O Lidar Measurements Challenging in the UTLS? 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 UTLS and therefore very challenging to detect…

GEWEX/GlobVapour Workshop, Mar 8-10, 2011, ESRIN, Frascati, Italy Resulting in a Long and Winding Road… Oct 2006: Validation campaign MOHAVE  Fluorescence Detected! Oct 2007: Validation campaign MOHAVE-II Fall 2008: H2O Raman lidar becomes an official NDACC instrument June Present: Routine measurements 2h/night, 3-4 nights per week April 2005: TMF WV Raman Lidar First Light Summer 2009: Six H2O Raman lidars provisionally accepted (need validation) Fall 2009: TMF H2O Raman lidar Validated 2002: NDACC considers Raman WV lidar as new NDACC instrument

GEWEX/GlobVapour Workshop, Mar 8-10, 2011, ESRIN, Frascati, Italy Oct 2006: Validation campaign MOHAVE  Fluorescence Detected! Oct 2007: Validation campaign MOHAVE-II Fall 2008: H2O Raman lidar becomes an official NDACC instrument June 2005 – Present: Routine measurements 2h/night, 3-4 nights per week April 2005: TMF WV Raman Lidar First Light Summer 2009: Six H2O Raman lidars provisionally accepted (need validation) Fall 2009: TMF H2O Raman lidar Validated  Resulting in a Long and Winding Road…

GEWEX/GlobVapour Workshop, Mar 8-10, 2011, ESRIN, Frascati, Italy Early Results: RS92 (corrected) vs. Lidar Comparison shows: Climatology (average of 202 profiles)  Lidar Very Wet or RS92 Very Dry or Both!

GEWEX/GlobVapour Workshop, Mar 8-10, 2011, ESRIN, Frascati, Italy A Long and Winding Road… Oct 2006: Validation campaign MOHAVE  Fluorescence Detected! Oct 2007: Validation campaign MOHAVE-II Fall 2008: H2O Raman lidar becomes an official NDACC instrument June Present: Routine measurements 2h/night, 3-4 nights per week April 2005: TMF WV Raman Lidar First Light Summer 2009: Six H2O Raman lidars provisionally accepted (need validation) Fall 2009: TMF H2O Raman lidar Validated 

GEWEX/GlobVapour Workshop, Mar 8-10, 2011, ESRIN, Frascati, Italy MOHAVE Campaign (Oct 2006): Fluorescence Detected Strong Rayleigh signal (355 nm) induces fluorescence in lidar receiver Comparison below shows lidar vs. CFH mean profiles when 355 nm blocked at the receiver’s entrance (right), and when 355 nm is not blocked (left)  New anti-fluorescent optics were ordered, custom-made and installed on the TMF lidar during summer 2007

GEWEX/GlobVapour Workshop, Mar 8-10, 2011, ESRIN, Frascati, Italy Since July 2007: Fluorescence is gone RS92 (corrected) vs. Lidar Comparison shows: by Season (154 profiles) The corrected RS92 is still too dry: Not a lidar problem anymore

GEWEX/GlobVapour Workshop, Mar 8-10, 2011, ESRIN, Frascati, Italy A Long and Winding Road… Oct 2006: Validation campaign MOHAVE  Fluorescence Detected! Oct 2007: Validation campaign MOHAVE-II Fall 2008: H2O Raman lidar becomes an official NDACC instrument June Present: Routine measurements 2h/night, 3-4 nights per week April 2005: TMF WV Raman Lidar First Light Summer 2009: Six H2O Raman lidars provisionally accepted (need validation) Fall 2009: TMF H2O Raman lidar Validated 

GEWEX/GlobVapour Workshop, Mar 8-10, 2011, ESRIN, Frascati, Italy Prior to 2009: No Water Vapor Lidars in NDACC (as of 2008)

GEWEX/GlobVapour Workshop, Mar 8-10, 2011, ESRIN, Frascati, Italy (as of 2009) Since 2009: Six Water Vapor Lidars provisionally in NDACC “Provisionally” because (more) validation is required

GEWEX/GlobVapour Workshop, Mar 8-10, 2011, ESRIN, Frascati, Italy A Long and Winding Road… Oct 2006: Validation campaign MOHAVE  Fluorescence Detected! Oct 2007: Validation campaign MOHAVE-II Fall 2008: H2O Raman lidar becomes an official NDACC instrument June Present: Routine measurements 2h/night, 3-4 nights per week April 2005: TMF WV Raman Lidar First Light Summer 2009: Six H2O Raman lidars provisionally accepted (need validation) Fall 2009: MOHAVE-2009 Campaign TMF H2O Raman Lidar Validated 

GEWEX/GlobVapour Workshop, Mar 8-10, 2011, ESRIN, Frascati, Italy October 2009: TMF Lidar Profiles Fully Validated Latest (optimized) receiver configuration since July 2009 Comparison below shows lidar vs. CFH mean profiles during MOHAVE-2009 Below 14 km: Average of 12 one-hour-integrated profiles coincident with balloon Above 14 km: Average of 8 full nights with coincident CFH flights

GEWEX/GlobVapour Workshop, Mar 8-10, 2011, ESRIN, Frascati, Italy Conclusions and Perspectives TMF Water Vapor Lidar Program: Started in 2005 Re-Analysis Back to 2007: Expected to be Available Late 2011 Period : Plagued with fluorescence (no satisfactory results above 12 km) Early Analysis ( ): Pronounced Annual Cycle (summer max)

GEWEX/GlobVapour Workshop, Mar 8-10, 2011, ESRIN, Frascati, Italy TMF = Significant NDACC past and present contribution to Ozone and Temperature Trends… THANK YOU ! from Steinbrecht et al., 2008 OZONETEMPERATURE km water vapor anomaly (%) ? Table Mountain WATER VAPOR Please visit JPL-TMF lidar website: Back to NDACC (long-term) Context We hope for a similar contribution for Water Vapor… in 2030!

GEWEX/GlobVapour Workshop, Mar 8-10, 2011, ESRIN, Frascati, Italy Backup Slides

GEWEX/GlobVapour Workshop, Mar 8-10, 2011, ESRIN, Frascati, Italy Tropopause All RS92 Temperature Profiles: WMO TP in Blue Cold-Point TP in red Text Typically Two Regimes: Well-defined Tropical-Type Unique Cold-Point TP in Summer Separate WMO and Cold-Point TP Typical of mid-lat. in Winter

GEWEX/GlobVapour Workshop, Mar 8-10, 2011, ESRIN, Frascati, Italy 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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