Transcript Ground Based Lidar to Profile Tropospheric CO2 - Update John Burris

Ground Based Lidar to Profile Tropospheric CO2 - Update
John Burris1, Arlyn Andrews2, Haris Riris1, Jim Abshire3, Amelia Gates4, Mike Krainak5 and Xiaoli Sun1
1Code
694, NASA Goddard Space Flight Center, Greenbelt, Md. 20771
Email: [email protected]
2CMDL/NOAA,
3
Boulder, Co. 80305
Code 690, NASA Goddard Space Flight Center, Greenbelt, Md. 20771
4GEST,
5Code
UMBC, Baltimore, Md. 21250
554, NASA Goddard Space Flight Center, Greenbelt, Md. 20771
Poster 4.2 - P
Why Profile CO2 from the Ground
Breadboard Profiling Lidar
Some Sample Measurements
• CO2 an important driver for climate change. Currently only
approximately half of the CO2 produced by man can be
accounted for in the atmosphere and oceans, the rest is
believed to have disappeared into terrestrial sinks whose
location is not known to better than continental scale resolution.
• DIAL Lidar approach in the 1572 nm CO2 absorption band
•The first peak is the online wavelength
• Measure backscatter profiles with laser tuned off & on a
selected CO2 line.
• Online profile has more counts because DFB laser emits
more power at this wavelength.
• Ratio of profiles yields extinction caused by CO2 absorption.
• Identifying location and size of sinks is crucial to
understanding their mode of operation and being able to
characterize their long term behavior.
• Measurement sensitive only to CO2. On and off-line
wavelengths separated by ~0.15 nm.
• Fall off caused by interface between PBL& free
troposphere
• Being able to measure CO2 concentrations within the planetary
boundary layer provides a mechanism to locate sinks on both
local and regional scales.
• Pulse width ~100 ns; Pulse rate 10 kHz for each wavelength
• Combining measurements of CO2’s spatial and temporal
variability with a transport model permits fluxes to be
calculated.
• Fiber lasers leverage telecommunications technology.
• 25 microsecond delay between each channel.
• Laser pulse energy: ~ 2-5 microjoules/pulse.
•The fluxes can be used with an inverse model to identify local
and regional CO2 sinks.
• Detector: InGaAs photon counting PMT. 4% quantum
efficiency.
• Height resolved CO2 measurements are now made using tall
(typically TV) towers;
• Online (1571.111 nm) and
offline (1570.96 nm) profiles
PBL – free trop
interface
• 6 minutes integration time.
• Smoothed on and offline range resolved aerosol returns.
Bin size = 30 m.
• Generally <500 meters tall with in-situ sensors capable of
measuring CO2 at < 1ppmv precision.
• Online profile falls off more rapidly than offline profile .
•Shows measurement of atmospheric CO2 extinction
Goals
• Develop & demonstrate a ground based CO2 profiling lidar,
constructed from commercial parts, which can operate
autonomously
• Goal to measure height resolved CO2 profiles to top of
boundary layer with a precision of 1 ppmv at least every hour.
• Use differential absorption lidar (DIAL) technique. This
approach has been successfully employed in the measurement
of stratospheric ozone to a precision of 1%.
• Use micro-pulse lidar approach as a model - ie a compact, selfcontained reliable & eyesafe lidar capable of autonomous
operation for months in remote locations
Calculated Performance
• Cost goal per unit <$200K.
• Profiler’s measurements of CO2’s spatial and temporal
variability can be used with transport models to derive fluxes.
• Calibration and validation tool for field studies and space
missions (eg OCO) cal/val.
•Aerosol backscatter coefficient  =
1.6*10-7 m-1 sr-1.
• Profiler can acquire data over a period of >4 hours unattended.
• Demonstrated ability to lock laser wavelengths to better than 1
pm, the resolution limit of the instrument making the
measurement. Goal is better than 0.5 pm.
• 10 kHz operation at each wavelength with 100 ns pulses.
August 21-25, 2006
• Test using two Mach-Zender modulators in series to better
extinguish leakage in transmitter.
• Retrieve longer series of on & off-line profile.
•Simulations of profiler measurement
precision for fiber laser () and
optical parametric amplifier (+) for 10minute signal averaging.
Current Status
Near Term Plans
• Calculate series of CO2 concentration profiles.
• Evaluate performance of Optical Parametric Amplifier based
laser (from ITT). Expect higher per pulse energies.
• Evaluate cooled HgCdTe APDs as possible replacement
detectors. Potentially higher QEs at 1570 nm and low
noise. Rugged construction & expect longer lifetime .
• Fiber laser has 15 J per pulse.
• OPA laser has 150 J per pulse at
10 kHz
ACKNOWLEDGEMENTS
We would like to gratefully acknowledge the support provided by NASA’s Tropospheric
Chemistry Program, the Laser Risk Reduction Program and internal Goddard support
including resources from the Earth Sciences Directorate. Last but not least the support,
collaboration and encouragement provided by the CO2 Sounder team headed by Dr. James
Abshire is greatly appreciated.
Joint Workshop on NASA Biodiversity, Terrestrial Ecology, and Related Applied Sciences