New perspectives for eddy covariance flux measurements using aircraft-based technology
Desjardins, R.L., Worth, D.E., Mauder, M., Pattey, E., Metzger, S. and MacPherson, I. 2016. New perspectives for eddy covariance flux measurements using aircraft-based technology. 32nd Conference on Agricultural and Forest Meteorology, Utah 2016/06/20 - 2016/06/24.
Plain language summary
This research contributes to a growing body of work that examines the problem of a measured energy imbalance at the Earth’s surface. Currently, most research finds that radiant energy arriving at the Earth’s surface is significantly (10 – 20 %) greater than the energy leaving the Earth’s surface. This cannot be, and is commonly referred to as the ‘flux underestimation’ problem. Results from a series of aircraft-based flux measurement campaigns spanning more than 10 years, and that cover a range of ecosystems are analyzed using the wavelet analysis approach. Wavelet analysis is an emerging technique to estimate the flux of mass (e.g. carbon dioxide) or energy (e.g. temperature) from the land surface, and allows results to be interpreted in both frequency (high to low) and in space (or time). This analysis shows that for all ecosystems studied, the fraction of the total flux found in the low-frequency range is significant (5 – 30 %) and varies day to day. Although this research does not solve the problem of flux underestimation, it demonstrates the importance of low-frequency flux contributions. Additional study is recommended that examines the relationship between landscape variability or patchiness, low-frequency flux contribution and flux underestimation at the Earth’s surface.
Much progress has been achieved during the last thirty years in measuring mass and energy exchange using aircraft-based sensors. Large scale projects over agricultural and forested regions have given scientists the opportunity to test and improve flux measurement techniques. As part of these projects, fluxes of latent and sensible heat as well as CO2 and O3 have been obtained over extended periods of time, over a wide range of spatial scales, using measurements from tower and aircraft-based systems. The progress achieved and lesson learned will be reviewed. The frequently mentioned problem of the underestimation of fluxes using the eddy covariance technique will be discussed. One of the main causes of the lack of energy budget closure is most likely mesoscale transfer. Aircraft-based flux measurements can provide valuable information on this topic. Using wavelet analysis, the magnitude of this transfer will be presented for several scalars for a wide range of landscapes. The use of wavelet analysis to minimize the impact of non-stationary conditions on eddy covariance estimates will also be discussed.