Time-frequency analysis of turbulence
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Time-frequency analysis of turbulence

Time-frequency analysis of turbulence, CO2 and energy fluxes above different ecosystems

Land vegetation feels the unprecedented pressure of a changing climate. A better understanding of how plants respond to environmental pressures such as heat waves and droughts will enable to design better mitigation measures. Eddy covariance is the leading method for monitoring greenhouse gas fluxes, providing direct and continuous measurements relevant to climate change. The products emanating from the eddy covariance method have become the standard reference for all flux related research such as studies on droughts, atmospheric inversions, satellite validation, and the like.

Turbulence is generated by buoyancy and mechanical shear and forms coherent structures, co- called eddies, that vertically mix the air of the canopy with the air of the atmosphere above. Gas concentrations coming from sources (respiration) and sinks (photosynthesis) are transported turbulently by these eddies from within the canopy to the atmosphere above the vegetation. The contributions of the eddies to the net ecosystem flux are estimated by analysing the 3D wind velocity and gas concentrations measured above the ecosystem by a flux tower.
The analysis in time-frequency space allows a more precise understanding of how turbulence and the characteristics of the eddies change throughout the day. In particular, it leads to a better estimation of fluxes by isolating the fluxes transported by eddy from signals of disturbances such as subsidence or large-scale horizontal inhomogeneities. We recently developed a wavelet-based method to analyse and estimate fluxes in time-frequency space. One important step is the detection and tracking of the band of frequencies occupied by the eddies within time-frequency space. This might be difficult with the current method if the eddy covariance tower is very tall. The objective of the master thesis is:

  • to test and analyse the estimations obtained with the new, wavelet-based method at an agricultural site and at a forest site with a very tall tower; and
  • to explore possible improvements of the method for the detection and tracking of the frequency band occupied by eddies.

We are seeking a motivated candidate who is eager to work in an interdisciplinary setting at the intersection of signal processing, fluid mechanics, and ecophysiology. This internship will build on recent work and has the potential to be continued in a PhD thesis.


Supervisors: Matthias Cuntz, Gabriel Destouet
Where: UMR Silva, INRAE Centre Grand Est – Nancy, Champenoux
When: 6 months in spring 2025
Application: send your CV and a motivation letter to matthias.cuntz and gabriel.destouet (at) inrae.fr

Modification date: 13 November 2024 | Publication date: 13 November 2024 | By: Corinne Martin