An aircraft-based data analysis method for discerning individual fluxes in a heterogeneous agricultural landscape Scott Kirby a, *, Ronald Dobosy b , Derek Williamson a , Ed Dumas b a University of Alabama, Department of Civil, Construction, and Environmental Engineering, Box 870205, Tuscaloosa, AL 35487-0205, USA b National Oceanic and Atmospheric Administration (NOAA) Atmospheric Turbulence and Diffusion Division (ATDD), 456 South Illinois Avenue, Oak Ridge, TN 37830, USA 1. Introduction Terrestrial carbon budgets worldwide are currently being studied on the full range of scales, both temporal and spatial, to determine areas with high carbon sequestration potential and to develop accurate global carbon budgets (Sellers et al., 1997; Melillo et al., 1993; Oechel et al., 1993; Soegaard et al., 2003; Cha ´ vez et al., 2005; Fan et al., 1998). Because these budgets ultimately have a global scale, satellite-based model- ing is a critical component of this effort. Many of these models are calibrated using flux towers each of which explicitly represents less than 1 km 2 of surface (their ‘‘footprint’’). The fidelity with which these widely-spaced tower-based flux measurements represent the landscape is a continuing question. Aircraft-based flux platforms have been used to address this spatial uncertainty for more than twenty years (Lenschow et al., 1981; Desjardins et al., 1982). Technological advances in instrumentation have allowed aircraft data to be viewed with the same confidence as tower data, the difference being in the agricultural and forest meteorology 148 (2008) 481–489 article info Article history: Received 6 February 2007 Received in revised form 14 October 2007 Accepted 17 October 2007 Keywords: Aircraft Carbon dioxide Flux Regional scale Land use Heterogeneous abstract The utility of aircraft-based flux data is hindered in heterogeneous landscapes by the averaging length required for proper flux calculations. In regions where the scale of heterogeneity is smaller than the traditional 3–5 km averaging length, it has been proble- matic to relate measured flux signals to an individual land use. This paper introduces the ‘‘Flux Fragment’’ method (FFM) which is based on traditional eddy-covariance flux techni- ques but uses a conditional sampling scheme to better segregate flux signals by surface type with aircraft-based data. Flux measurements from a low-flying aircraft and from towers were obtained as part of a campaign in the ‘patchy’ agricultural landscape of the Midwestern United States. The fluxes from maize and soybean were computed and compared to the tower-based flux signals from both land uses. The FFM-derived fluxes of CO 2 clearly discern the maize and soybean signals in all midday flights and display the same diurnal patterns as observed using the flux towers. The quantitative match between airborne and fixed measures of CO 2 exchange is good, but displays significant discrepancies. The discrepancies arise, we argue, from the natural variation in flux within the same land-use class over the landscape, a variation invisible to a single tower. Spatially averaged fluxes from the FFM complement towers’ temporal coverage to provide an improved basis for scaling local fluxes to regional estimates based on total areas of each land use. # 2007 Elsevier B.V. All rights reserved. * Corresponding author. E-mail address: SAK4UA@yahoo.com (S. Kirby). available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/agrformet 0168-1923/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.agrformet.2007.10.011