New perspectives for eddy covariance flux measurements using aircraft-based technology

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.