As there are many techniques available for measuring these fluxes in the boundary layer, the group considered that it would be useful to start by discussing seven principal ones in turn.

The vertical flux (or eddy transport) F of any atmospheric parameter ψ may be represented by

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where w is the wind's vertical component, and the prime denotes the instantaneous deviation of the quantity from its mean value (e.g. w″ = w″ − inline image [Priestley, 1959]. It is important to choose the sampling rate and the observational period so that the required parts of the total flux spectrum are measured [Pasquill, 1962].