B53A-0173:
Using aircraft eddy-covariance measurements to examine the spatial heterogeneity of CO2 exchange above three temperate forests

Friday, 19 December 2014
Dana Caulton1, Paul B Shepson2, David Y Hollinger3, J. William Munger4, Sassan S Saatchi5, Mahta Moghaddam6, Paul R Moorcroft7, Stefan Metzger8 and Brian H Stirm2, (1)Purdue University, Chemistry, West Lafayette, IN, United States, (2)Purdue Univ, West Lafayette, IN, United States, (3)USDA Forest Service, Durham, NH, United States, (4)Harvard University, Cambridge, MA, United States, (5)NASA Jet Propulsion Laboratory, Pasadena, CA, United States, (6)University of Southern California, The Ming Hsieh Dept. of Electr. Eng., Los Angeles, CA, United States, (7)Harvard Univ, Cambridge, MA, United States, (8)NEON, Fundamental Instrument Unit, Boulder, CO, United States
Abstract:
Regional and global scale ecosystem models often rely on data from flux towers to simulate the surface-atmosphere exchange of CO2. Such data represent comparatively small source areas (~1 km2) and in many cases exhibit relatively homogeneous land use and surface characteristics. This approach assumes that the small-scale observations yield representative results for larger regions that can be more heterogeneous in terms of land cover, soil moisture, topography and climatology. To complement this data source, aircraft platforms can be used to provide snapshot views of land cover and meteorological properties. Moreover, aircraft provide access to essentially any environment including remote and heterogeneous regions.

Here, we used an instrumented aircraft platform equipped with a 50 Hz wind probe, Global Navigation Satellite System/Inertial Measurement Unit and a 10 Hz Picarro CO2/H2O analyzer. Applying the eddy-covariance technique, this platform permits determining the surface-atmosphere exchange of heat and CO2 fluxes over larger (~101–102 km2) spatial scales. Specifically, thirty-eight flux measurement experiments were conducted as part of the Airborne Observatory of Subcanopy and Subsurface (AirMOSS) campaigns in July, 2012 and May-August, 2013. Each experiment targeted specific land cover types over and near Howland Forest, ME, Harvard Forest, MA and Duke Forest, NC.

A footprint parameterization is used to determine the contribution of different surface sources to the flux measurements. The surface area contributing to the measured fluxes is typically on the order of 37 ± 17 km2, with 90% of the contributions being sourced from within an upwind distance of 1.9 ± 0.8 km. Combining the knowledge of these source areas with land cover and soil moisture data from the NASA G-III aircraft enables investigating the influence of surface heterogeneity on the measured fluxes. Lastly, the measured fluxes are compared to simulated CO2 fluxes from the Ecosystem Demography-2 model, which explicitly incorporates spatial variability in many variables including land cover and soil moisture.

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