Atmospheric CO 2 Concentration Measurements to Cloud Tops with an Airborne Lidar Jianping Mao 1, Anand Ramanathan 1, James B. Abshire 2, S. Randy Kawa 2, Haris Riris 2, Graham R. Allan 3, Michael Rodriguez 3, William E. Hasselbrack 3, Xiaoli Sun 2, Kenji Numata 2, Jeff Chen 2, Yonghoon Choi 4, Mei Ying Melissa Yang 4 1 University of Maryland, College Park, MD 20740, USA 2 NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA 3 Sigma Space Inc., Lanham, MD 20706, USA 4 NASA Langley Research Center, Hampton, VA 23681, USA JM 1
Outline Range & Height-Resolved Backscatter Surface Roughness cloud tops Surface Reflectance cloud tops XCO 2 Retrievals to Cloud Tops Resolving CO 2 Gradient Summary and Discussion JM 2
Where are the clear skies? JM 3
Measurement Challenges I total I 0 r I I on off e c on c off ( )/ I direct I diffuse atmospheric state (P, T, H 2 O) & XCO 2 Scattering Cloud FOV photon path length advantage of lidar ranging capability JM 4
Measurement Approach - highlights Measurement Approach Pulsed laser and time-gated receiver >> Height-resolved backscatter measurements >> High spectral resolution, high measurement sensitivity Multiple-wavelength measurement cross one CO 2 absorption line >> Lineshape-resolved w/ 30 wavelengths >> very narrow spectral coverage (< 0.15 nm) Fixed nadir-pointed Measurement Parameters 1-μs laser pulse width 10 khz pulse rate ~ a step of 100-μs 300 Hz laser scan rate cross 30 wavelengths on the 1572.335 nm CO 2 line 10 Hz receiver data recording rate for all wavelengths ~ 0.1 s raw data reporting interval 10 ns receiver bin width ~ up to 1.5 m vertical resolution JM 5
Lidar Ranging Capability 25 cm to flat surface over a horizontal path (Amediek et al., 2013) 2.8 m over the water surface of Chesapeake Bay when compared to GPS JM 6
CO 2 Sounder Lidar Backscatter Profiles Cirrus Cumulus Flight to Iowa, 8/10/2011; Height-resolved; Clearly-separated line shapes for returns from elevated surfaces ground, cumulus and cirrus cloud tops cirrus cumulus CO 2 ground JM 7
Surface Roughness Measurements Aug. 22, 2014 ASCENDS flight over Pacific Ocean near California coast S.D. = 0.49 m within 0.1 second S.D. = 0.96 m within 5 seconds JM 8
Surface Roughness Measurements Aug. 20, 2014 ASCENDS flight over stratus clouds along California coastline S.D. = 5.3 m within 0.1 second S.D. = 17.6 m within 5 seconds JM 9
Surface Roughness Measurements Aug. 25, 2014 ASCENDS flight above cumulus clouds in Iowa S.D. = 42 m with 0.1 second S.D. = 107 m within 5 seconds JM 10
Surface Reflectance Measurements Aug. 25, 2014 ASCENDS flight above cumulus clouds in Iowa Kuze et al., 2010 Cumulus 5% vs. 20% Ground 1 μs ~ 150-m vertical layer JM 11
XCO 2 Measurements Aug. 2, 2011, above marine stratus clouds along California coastline optimal meas. range cloud top 10-s average Bias < 1 ppm S.D. 2~3 ppm, small sample size JM 12
XCO 2 Measurements to cumulus cloud tops Aug. 10, 2011 flight in Iowa 10-s average S.D. 2~3 ppm, clear sky S.D. 4-6 ppm, cumulus clouds cloud tops clear small sample size 20 ppm Drawdown over cornfield JM 13
XCO 2 Measurements to Cloud Tops Aug. 25, 2011 sunset flight to Iowa spiral WBI A B Find continuous cloud cover > 5 minutes Large sample size > 30 retrievals Similar flight altitude JM 14
Backscatter cross-section for Segment A & B 7-minute cumulonimbus cumulus ground Segment A 7 minutes cumulus cloud tops ~ 2 km Segment B ~ 30 minutes cumulus ~ 1.5 km altocumulus ~ 3.5 km 10-minute altocumulus cumulus ground JM 15
XCO 2 Measurement Comparison Segment A vs Segment B Parameterized Chemical Transport Model (PCTM; Kawa et al., 2004, 2010) cumulus flight altitude ~ 5.5 km S.D. 1.60 ppm clear 1.85 ppm cumulus 4.47 ppm altocumulus Cumulonimbus Cumulus XCO 2 =389 ppm N = 32 Segment B 393 ppm N = 28 ground cumulus 395.8 ppm N = 39 altocumulus Segment A XCO 2 =395.2 ppm N=40 395.4 ppm - AVOCET XCO 2 measurements to cloud tops help resolving horizontal and vertical gradient!!! JM 16
XCO 2 Measurements to Cirrus Cloud Tops Stratosphere cumulus aircraft 1.6 km cirrus clouds In situ: 392.4 ppmv Cumulonimbus Cumulus only dense cirrus allow quality retrieval short absorption path length for airborne measurements stronger absorption signal for space-borne JM 17
Summary Demonstrated CO 2 measurement capability to cloud tops using NASA/ CO 2 Sounder lidar Demonstrated XCO 2 to cloud tops help resolving CO 2 gradients and vertical structure Full data coverage and sampling will improve carbon flux estimate OSSE studies are needed to evaluate the benefits of the partial column XCO 2 measurements Acknowledgement: This work was funded by the NASA ESTO IIP-10 program and the NASA ASCENDS formulation activity. We also thank DC-8 team at NASA Armstrong Flight Center for helping plan and conduct the flight campaigns. JM 18
Timeline of Measurement Progress Detector InGaAs PMT HgCdTe APD Laser Source Free Scanning Step-Locked CO 2 Sounder Instrument Timeline Detector Nonlinearity (ppm) X CO2 scatter (ppm) 30 20 10 0 6 4 2 10s ave 1s ave 0 2010 2011 2012 2013 2014 2015 2016 2017 Year clear-sky JM 19
Column Retrieval through aerosol layers 8/22/2014 Std. dev. Time-gated and range-resolved measurements: 1) minimize atmospheric scattering effect and yield low-biased retrievals; 2) minimizes retrieval errors over rough surfaces (terrains, tree covers) JM 20
Lidar Cloud Slicing allows CO 2 measurements at several altitudes JM 21