Footprint Estimation for Multi-Layered Sources and Sinks Inside Canopies in Open and Protected Environments

Abstract

A multi-layered flux footprint model is developed for a canopy situated within a protected environment such as a screenhouse. The model accounts for the vertically distributed sources and sinks within the canopy as well as modifications introduced by the screen on the flow field and micro-environment. The effect of the screen on fetch as a function of its relative height above the canopy is then studied and compared to the case where the screen is absent. It is found that the required fetch is not appreciably affected by the vertical source–sink distribution in open and protected environments, but changes with the canopy density. Moreover, the fetch-to-height ratio is increased by the presence of the screen, at least when compared to the open environment case. How footprint analysis can be employed to estimate the ratio between above-canopy measured flux and vertically-integrated canopy source–sink strengths in a prototypical screenhouse is illustrated and further evaluated against eddy-covariance measurements from two screenhouse experiments.