The surface renewal method offers an inexpensive way to estimate the sensible heat flux (H). When combined with measurements of net radiation and soil heat flux, latent heat flux (evapotranspiration) can be estimated indirectly. This study evaluated the performance of two surface renewal models to estimate H in a traditional coffee agroforestry system. The first model (Snyder96) is the commonly used approach in which H is calculated from the average temperature ramp amplitude and duration, which in turn are calculated from the 2nd, 3rd, and 5th order structure functions. The second model (Chen97) is a reformulation of Snyder96 in which H is calculated from the 3rd order structure function and friction velocity (u_*). The models were calibrated and evaluated with eddy covariance data. Tests were conducted at three levels (above-canopy, above-coffee, above-ground), with each level having two replicate plots. Both models showed generally good agreement with the observations when using humidity-corrected sonic temperature data. Estimates from Chen97 agreed slightly better with measurements than those from Snyder96. In addition, the results suggest that for Chen97 the same calibration can be used for the above-canopy and above-coffee levels and for positive and negative H. Also for the above-ground level the combined empirical coefficient of Chen97 was similar to those for the other levels, but the variability between plots was too high to draw conclusions. Conversely, the results showed that Snyder96 requires separate calibrations for each level and for positive and negative H. For Chen97, similarly good results were obtained when using frequency response-corrected thermocouple data. For Snyder96, results were also good above the canopy, but not within the canopy, particularly close to the ground. Chen97 needs wind speed to calculate u_*. Wind speed is needed for both models if the signals of thicker, stronger thermocouples are corrected for the frequency response error.

表面更新方法提供了一种估算显热通量 ( H )的廉价方法。当与净辐射和土壤热通量的测量相结合时，潜热通量（蒸散量）可以被间接估计。本研究评估了两种表面更新模型在传统咖啡农林业系统中估计H的性能。第一个模型 (Snyder96) 是常用的方法，其中H是根据平均温度斜坡幅度和持续时间计算的，而后者又是根据 2 阶、3 阶和 5 阶结构函数计算的。第二个模型 (Chen97) 是 Snyder96 的重新表述，其中H是根据三阶结构函数和摩擦速度 ( u_* )。使用涡流协方差数据校准和评估模型。测试在三个级别（树冠上方、咖啡上方、地上）进行，每个级别有两个重复地块。当使用湿度校正的声波温度数据时，两种模型都显示出与观察结果的总体良好一致性。Chen97 的估计值与测量值的一致性略好于 Snyder96 的估计值。此外，结果表明，对于 Chen97，相同的校准可用于冠层以上和咖啡以上水平以及正负H. 同样对于地上水平，Chen97 的综合经验系数与其他水平的相似，但地块之间的变异性太高，无法得出结论。相反，结果表明 Snyder96 需要对每个水平以及正负H进行单独校准。对于 Chen97，使用频率响应校正的热电偶数据时获得了类似的良好结果。对于 Snyder96，在树冠上方的结果也不错，但在树冠内，尤其是靠近地面的位置则不然。Chen97 需要风速来计算u _*。如果针对频率响应误差校正更粗、更强的热电偶的信号，则两种模型都需要风速。