Minimizing the Impact of Thin Clouds on CO2 Measurements from an Intensity-Modulated Continuous-Wave Laser Absorption Spectrometer

Fenton Wallace Harrison, NASA Langley Research Center, fenton.w.harrison@nasa.gov (Presenter)
Jeremy Todd Dobler, ITT Space Systems Division, LLC, jeremy.dobler@itt.com
Bing Lin, NASA Langley Research Center, bing.lin@nasa.gov
Douglas McGregor, ITT Space Systems Division, LLC, douglas.mcgregor@itt.com
Edward V. Browell, NASA Langley Research Center, edward.v.browell@nasa.gov
Susan Kooi, SSAI, susan.a.kooi@nasa.gov

Accurate understanding of carbon balance in the environment is critical to projections of the future evolution of the Earth’s climate. Uncertainties in the modeling of carbon sources and sinks remain large due to the limited set of observations from the current network of in-situ and surface measurements. Global, spaceborne measurements of atmospheric CO2 can reduce these uncertainties, and the National Research Council (NRC) Decadal Survey of Earth Science and Applications from Space identified Active Sensing of CO2 Emissions over Nights, Days, and Seasons (ASCENDS) as an important mid-term (Tier II) mission. The active space remote XCO2 measurement that is called for in the ASCENDS mission requires the simultaneous measurements of CO2 and O2 number density columns to derive the average CO2 mixing ratio (XCO2) column. The NRC recommendation calls for XCO2 to be measured to a precision of less than 2 ppm and must be made with minimum biases from aerosols, dust, or clouds. This paper discusses algorithms for minimizing the impact of thin clouds on remote measurements of CO2 obtained from an intensity-modulated (IM) continuous-wave (CW) laser absorption spectrometer (LAS) that is under development for the ASCENDS mission.

A prototype ASCENDS LAS measurement system, called the Multi-frequency Fiber Laser Lidar (MFLL) was tested during two flight campaigns in 2011 using an encoded intensity-modulated (IM) continuous-wave (CW) modulation scheme to minimize the impact of thin clouds on CO2 measurements. MFLLhas demonstrated the ability to simultaneously measure CO2 and O2 number density columns using wavelengths near 1.57 and 1.26 μm, respectively. The MFLL also simultaneously measures range to the surface. Ultimately, these three components are combined to produce a dry air equivalent column mixing ratio (XCO2).

This paper describes the encoded thin cloud rejection modulation technique, presents preliminary flight test results for encoded modulation technique, and discusses algorithms for minimizing bias from thin clouds on CO2 retrievals.

Presentation: 2011_Poster_Harrison_34_306.pdf (8657k)

Presentation Type:  Poster

Session:  Coupled Processes at Land-Atmosphere-Ocean Interfaces   (Mon 4:00 PM)

Associated Project(s): 

• Moore, Berrien: Advancing Our Understanding of the Earth System Through Coupled Carbon-Climate Modeling and Observations ...details

Poster Location ID: 34