*3.1. Energy Balance Closure*

The energy balance closure is a typical method for evaluating the reliability of the EC system's measurements. A half-hourly linear regression analysis was performed between the available energy fluxes (*Rn* − *G*) and the turbulent fluxes (*LE* + *H*) measured from the EC system (Figure 3).

**Figure 3.** Half-hourly regression analysis between (*Rn* − *G*) and (*LEEC* + *HEC*).

In this study, measurements of the EC system were used to evaluate the performance of the SR method. Although the shortage of energy balance was within the accepted range, the estimation of *LE* using the SR method was based on the energy balance Equation (11):

$$LE\_{\rm EC} + H\_{\rm EC} = 0.64 \text{ ( $R\_n - G$ )}\tag{11}$$

The overall results showed that both fluxes were in good agreement, with relatively high *R2* = 0.85, a slope of regression of 0.64, and statistical errors *RMSE* and *RE* of 25.13 W·m−<sup>2</sup> and 3.72%, respectively. The energy balance slope was within the acceptable range related to the EC system application in the literature [38,39]. Hence, measurements of the EC system including the sensible heat flux and latent heat flux were used to calibrate the performance of the surface renewal method in this study.

The coherent movements of the fluxes cannot be justified by either the surface renewal or the eddy covariance method, and their role in the post-field data processing involving both of these methods remains unknown. However, this issue can play a critical role for elucidating the surface energy balance closure when the SR method is used.

### *3.2. The Footprint of EC Flux Measurements*

A footprint model was applied to analyze the relative contribution of the windward distance to surface fluxes measured by the EC system. The footprint model was estimated by Equations (1)–(3), which provide the ratio between 90% flux footprint and measurement height; Equation (1). The analysis was performed mostly for the daytime (unstable conditions) [27]. Two days with different climatic conditions were selected from the experimental duration: One partly cloudy (27 November 2018) and the other one (18 October 2018) a sunny day. Diurnal variations of footprint/height ratios for these two days are shown in Figure 4:

**Figure 4.** Variation of half-hourly 90% footprint measurement height ratio of two different days [23].

The results in Figure 4 show that the ratio during the sunny day was in the range 0–30, significantly lower than the ratio determined during the partly cloudy day which ranged between 50 and 60. This difference is presumably because during the sunny day, the surface was warmer, and the boundary layer was more unstable than during the partly cloudy day. This larger instability resulted in a shorter 90% flux footprint during the sunny than the partly cloudy day. Besides, Figure 4 shows that on both days, the ratio was smaller than the common 100:1 fetch/height ratio. This indicates that under the conditions of this experiment, most of the flux measured by the EC system originated from within the tea field under study. Hence, the EC data are reliable and can be used for the calibration of the SR method [13].
