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

Wolfe, G. M.; Kawa, S. R.; Hanisco, T. F.; Hannun, Reem A.; Newman, Paul A.; Swanson, Andrew K.; Bailey, Sean W.; Barrick, J. D.; Thornhill, K. L.; Diskin, G. S.; DiGangi, Josh; Nowak, John B.; Sorenson, Carl; Bland, G.; Yungel, James K.; Swenson, C. A.

doi:10.5194/amt-11-1757-2018

Cited by 36 publications

(36 citation statements)

References 87 publications

(119 reference statements)

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“…All three show too much HF noise to resolve the inertial subrange of turbulence. Similar results are shown by Wolfe et al (2018) from low-level airborne carbon flux measurements over Maryland and Virginia. Beyond about 5 Hz (corresponding to 12 m horizontal distance at the typical airspeed of 60 m s −1 ) spectral drop-off due to dampening in the tubing is visible.…”

Section: Spectral Analysissupporting

confidence: 83%

“…We performed coherency and correlation analysis with spectral resolution and as integral statistics and could not find any correlation between pressure and the CH 4 signal. Also Wolfe et al (2018) reported no pressure effect on the CH 4 signal from an airborne LGR analyser.…”

Section: Methane Analysermentioning

confidence: 96%

“…At this point in time only few aircraft are capable of conducting methane flux measurements. Wolfe et al (2018) used a C-23 Sherpa and Desjardins et al (2017) used a Twin Otter to measure direct methane emission over mid-latitude agricultural areas. Over the Alaskan North Slope Sayres et al (2017) and Dobosy et al (2017) flew a Diamond DA42 for methane flux measurements.…”

Section: Introductionmentioning

confidence: 99%

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New calibration procedures for airborne turbulence measurements and accuracy of the methane fluxes during the AirMeth campaigns

et al. 2018

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Abstract. Low-level flights over tundra wetlands in Alaska and Canada have been conducted during the Airborne Measurements of Methane Emissions (AirMeth) campaigns to measure turbulent methane fluxes in the atmosphere. In this paper we describe the instrumentation and new calibration procedures for the essential pressure parameters required for turbulence sensing by aircraft that exploit suitable regular measurement flight legs without the need for dedicated calibration patterns. We estimate the accuracy of the mean wind and the turbulence measurements. We show that airborne measurements of turbulent fluxes of methane and carbon dioxide using cavity ring-down spectroscopy trace gas analysers together with established turbulence equipment achieve a relative accuracy similar to that of measurements of sensible heat flux if applied during low-level flights over natural area sources. The inertial subrange of the trace gas fluctuations cannot be resolved due to insufficient high-frequency precision of the analyser, but, since this scatter is uncorrelated with the vertical wind velocity, the covariance and thus the flux are reproduced correctly. In the covariance spectra the −7/3 drop-off in the inertial subrange can be reproduced if sufficient data are available for averaging. For convective conditions and flight legs of several tens of kilometres we estimate the flux detection limit to be about 4 mg m −2 d −1 for w CH 4 , 1.4 g m −2 d −1 for w CO 2 and 4.2 W m −2 for the sensible heat flux.

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Section: Spectral Analysissupporting

confidence: 83%

Section: Methane Analysermentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

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New calibration procedures for airborne turbulence measurements and accuracy of the methane fluxes during the AirMeth campaigns

et al. 2018

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“…Although some effort is made to capture subgrid variability by combining tower clusters (e.g., IMN, BON) and similar ecosystems (e.g., Figure 2) and by examining sensitivity to spatial resolution (e.g., Fig-ure S1), we caution that spatial representativeness issues remain in the flux tower-model comparisons. Airborne eddy covariance surveys provide a viable option to increase footprint size toward regional scale (Wolfe et al, 2018); (iii) flux partitioning of eddy covariance NEE into GPP and TER also carries large uncertainties and can yield very different results depending on method (e.g., Figure S1). This uncertainty in itself may explain the short time lags between thaw and GPP observed at Bonanza Creek.…”

Section: Limitations and Uncertainties For Eddy Covariance Observatmentioning

confidence: 99%

Spring photosynthetic onset and net CO₂ uptake in Alaska triggered by landscape thawing

Parazoo

Arneth

Pugh

et al. 2018

Global Change Biology

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The springtime transition to regional-scale onset of photosynthesis and net ecosystem carbon uptake in boreal and tundra ecosystems are linked to the soil freeze-thaw state. We present evidence from diagnostic and inversion models constrained by satellite fluorescence and airborne CO from 2012 to 2014 indicating the timing and magnitude of spring carbon uptake in Alaska correlates with landscape thaw and ecoregion. Landscape thaw in boreal forests typically occurs in late April (DOY 111 ± 7) with a 29 ± 6 day lag until photosynthetic onset. North Slope tundra thaws 3 weeks later (DOY 133 ± 5) but experiences only a 20 ± 5 day lag until photosynthetic onset. These time lag differences reflect efficient cold season adaptation in tundra shrub and the longer dehardening period for boreal evergreens. Despite the short transition from thaw to photosynthetic onset in tundra, synchrony of tundra respiration with snow melt and landscape thaw delays the transition from net carbon loss (at photosynthetic onset) to net uptake by 13 ± 7 days, thus reducing the tundra net carbon uptake period. Two global CO inversions using a CASA-GFED model prior estimate earlier northern high latitude net carbon uptake compared to our regional inversion, which we attribute to (i) early photosynthetic-onset model prior bias, (ii) inverse method (scaling factor + optimization window), and (iii) sparsity of available Alaskan CO observations. Another global inversion with zero prior estimates the same timing for net carbon uptake as the regional model but smaller seasonal amplitude. The analysis of Alaskan eddy covariance observations confirms regional scale findings for tundra, but indicates that photosynthesis and net carbon uptake occur up to 1 month earlier in evergreens than captured by models or CO inversions, with better correlation to above-freezing air temperature than date of primary thaw. Further collection and analysis of boreal evergreen species over multiple years and at additional subarctic flux towers are critically needed.

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“…Airborne eddy covariance (EC) provides neardirect measurements of surface-atmosphere exchange over landscape-to-regional scales (e.g. Lenschow et al 1981, Desjardins et al 1982, 1989, Crawford et al 1996, Sellers et al 1997, Gioli et al 2004, Sayres et al 2017, Wolfe et al 2018. Such observations have successfully been used to evaluate CH 4 emissions inventories (Hiller et al 2014) and to scale up tower-or aircraft-based fluxes via empirically-derived environmental response functions (Miglietta et al 2007, Metzger et al 2013, Zulueta et al 2013.…”

Section: Introductionmentioning

confidence: 99%

Spatial heterogeneity in CO₂, CH₄, and energy fluxes: insights from airborne eddy covariance measurements over the Mid-Atlantic region

Hannun

Wolfe

Kawa

et al. 2020

Environ. Res. Lett.

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The exchange of carbon between the Earth's atmosphere and biosphere influences the atmospheric abundances of carbon dioxide (CO 2 ) and methane (CH 4 ). Airborne eddy covariance (EC) can quantify surface-atmosphere exchange from landscape-to-regional scales, offering a unique perspective on carbon cycle dynamics. We use extensive airborne measurements to quantify fluxes of sensible heat, latent heat, CO 2 , and CH 4 across multiple ecosystems in the Mid-Atlantic region during September 2016 and May 2017. In conjunction with footprint analysis and land cover information, we use the airborne dataset to explore the effects of landscape heterogeneity on measured fluxes. Our results demonstrate large variability in CO 2 uptake over mixed agricultural and forested sites, with fluxes ranging from −3.4±0.7 to −11.5±1.6 μmol m −2 s −1 for croplands and −9.1±1.5 to −22.7±3.2 μmol m −2 s −1 for forests. We also report substantial CH 4 emissions of 32.3±17.0 to 76.1±29.4 nmol m −2 s −1 from a brackish herbaceous wetland and 58.4±12.0 to 181.2± 36.8 nmol m −2 s −1 from a freshwater forested wetland. Comparison of ecosystem-specific aircraft observations with measurements from EC flux towers along the flight path demonstrate that towers capture ∼30%-75% of the regional variability in ecosystem fluxes. Diel patterns measured at the tower sites suggest that peak, midday flux measurements from aircraft accurately predict net daily CO 2 exchange. We discuss next steps in applying airborne observations to evaluate bottom-up flux models and improve understanding of the biophysical processes that drive carbon exchange from landscapeto-regional scales.

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

Cited by 36 publications

References 87 publications

New calibration procedures for airborne turbulence measurements and accuracy of the methane fluxes during the AirMeth campaigns

New calibration procedures for airborne turbulence measurements and accuracy of the methane fluxes during the AirMeth campaigns

Spring photosynthetic onset and net CO₂ uptake in Alaska triggered by landscape thawing

Spatial heterogeneity in CO₂, CH₄, and energy fluxes: insights from airborne eddy covariance measurements over the Mid-Atlantic region

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

Cited by 36 publications

References 87 publications

New calibration procedures for airborne turbulence measurements and accuracy of the methane fluxes during the AirMeth campaigns

New calibration procedures for airborne turbulence measurements and accuracy of the methane fluxes during the AirMeth campaigns

Spring photosynthetic onset and net CO2 uptake in Alaska triggered by landscape thawing

Spatial heterogeneity in CO2, CH4, and energy fluxes: insights from airborne eddy covariance measurements over the Mid-Atlantic region

Contact Info

Product

Resources

About

Spring photosynthetic onset and net CO₂ uptake in Alaska triggered by landscape thawing

Spatial heterogeneity in CO₂, CH₄, and energy fluxes: insights from airborne eddy covariance measurements over the Mid-Atlantic region