Articles | Volume 11, issue 3
Research article
28 Mar 2018
Research article |  | 28 Mar 2018

The NASA Carbon Airborne Flux Experiment (CARAFE): instrumentation and methodology

Glenn M. Wolfe, S. Randy Kawa, Thomas F. Hanisco, Reem A. Hannun, Paul A. Newman, Andrew Swanson, Steve Bailey, John Barrick, K. Lee Thornhill, Glenn Diskin, Josh DiGangi, John B. Nowak, Carl Sorenson, Geoffrey Bland, James K. Yungel, and Craig A. Swenson

Abstract. The exchange of trace gases between the Earth's surface and atmosphere strongly influences atmospheric composition. Airborne eddy covariance can quantify surface fluxes at local to regional scales (1–1000 km), potentially helping to bridge gaps between top-down and bottom-up flux estimates and offering novel insights into biophysical and biogeochemical processes. The NASA Carbon Airborne Flux Experiment (CARAFE) utilizes the NASA C-23 Sherpa aircraft with a suite of commercial and custom instrumentation to acquire fluxes of carbon dioxide, methane, sensible heat, and latent heat at high spatial resolution. Key components of the CARAFE payload are described, including the meteorological, greenhouse gas, water vapor, and surface imaging systems. Continuous wavelet transforms deliver spatially resolved fluxes along aircraft flight tracks. Flux analysis methodology is discussed in depth, with special emphasis on quantification of uncertainties. Typical uncertainties in derived surface fluxes are 40–90 % for a nominal resolution of 2 km or 16–35 % when averaged over a full leg (typically 30–40 km). CARAFE has successfully flown two missions in the eastern US in 2016 and 2017, quantifying fluxes over forest, cropland, wetlands, and water. Preliminary results from these campaigns are presented to highlight the performance of this system.

Short summary
We describe a new NASA airborne system for directly observing the surface–atmosphere exchange of greenhouse gases and energy over regional scales. Such measurements are needed benchmark model and satellite products and can improve process-level understanding of greenhouse gas sources and sinks over forest, croplands, wetlands, urban areas, and other ecosystems.