Eddy covariance
The method analyses high-frequency wind and scalar atmospheric data series, gas, energy, and momentum,[1] which yields values of fluxes of these properties.
It is frequently used to estimate momentum, heat, water vapour, carbon dioxide and methane fluxes.
[14] The flux footprint area is dynamic in size and shape, changing with wind direction, thermal stability and measurements height, and has a gradual border.
The effect of sensor separation, finite sampling length, sonic path averaging, as well as other instrumental limitations, affect frequency response of the measurement system and may need a co-spectral correction, especially noticeable with closed-path instruments and at low heights below 1 to 1.5 m. In mathematical terms, "eddy flux" is computed as a covariance between instantaneous deviation in vertical wind speed (
As of 2011 there were many software programs[15] to process eddy covariance data and derive quantities such as heat, momentum, and gas fluxes.
The programs range significantly in complexity, flexibility, number of allowed instruments and variables, help system and user support.
[1][17] Micrometeorology focuses climate study on the specific vegetation canopy scale, again with applications to hydrological and ecologic research.
The effects of turbulence may for example be of specific interest to climate modelers or those studying the local ecosystem.
Wind speed, turbulence, and mass (heat) concentration are values that could be recorded in a flux tower.
Through measurements related to eddy covariance properties such as roughness coefficients may be empirically calculated, with applications to modeling.
[19] Fluxes of greenhouse gasses from vegetation and agricultural fields can be measured by eddy covariance as referenced in micrometeorology section above.
By measuring vertical turbulent flux of gas states of H2O, CO2, heat, and CH4 among other volatile organic compounds monitoring equipment can be used to infer canopy interaction.
[20] Vegetation production models require accurate ground observations, in this context from eddy covariant flux measurement.
Advancements in technology have allowed for minor fluctuations resulting in a scale of 100-2000 meter measurements of air mass and energy readings.
Using such information carbon flux between ecosystems and the atmosphere can be observed, with applications ranging from climate change to weather models.
[21][22] The main difference between the true and the relaxed eddy accumulation technique is that the latter samples air with a constant flow rate that is not proportional to the vertical wind speed.
