ABSTRACT

Plant water stress can be remotely monitored by means of thermography due to its increasing effect on plant temperature. For a more accurate estimation of plant water status, its temperature should be normalised against environmental conditions. In this paper, the aim was to investigate a recently proposed method of normalisation using artificial reference surfaces, different measurement times in a day and different capturing directions regarding to solar trail. At three different times of the day, frontal images were captured from the sunlit side of the olive canopies in two azimuth directions. Two different stress indices of crop water stress index (CWSI) and stomatal conductance index (I_G) were calculated using Tc and the temperatures of wet and dry reference surfaces. Trees in different stress levels discriminated better via mean canopy temperature (Tc) of morning measurements. At this time, Tc also provided higher correlated indices with stomatal conductance (SC) rather than those indices calculated based on Tc measured at noon and afternoon. Comparing two measurement directions, the first direction provided Tc with higher correlated indices at morning but the second direction at afternoon. In the most of the measurement conditions, stress indices calculated with air temperature plus five degrees as dry reference temperature had higher correlation with SC.

摘要

由于其对植物温度的影响越来越大，因此可以通过热成像对植物水分胁迫进行远程监测。为了更准确地估计植物水分状况，应根据环境条件对其温度进行标准化。在本文中，目的是研究最近提出的使用人工参考表面、一天中的不同测量时间和关于太阳轨迹的不同捕获方向的归一化方法。在一天中的三个不同时间，从橄榄树冠的阳光照射侧在两个方位角方向拍摄正面图像。缺水指数（CWSI）和气孔导度指数的两种不同的应力指数（I _ģ) 是使用 Tc 以及干湿参考表面的温度计算得出的。通过早晨测量的平均冠层温度 (Tc)，不同压力水平的树木可以更好地区分。此时，Tc 还提供了与气孔导度 (SC) 更高的相关指数，而不是那些基于中午和下午测量的 Tc 计算的指数。比较两个测量方向，第一个方向在早上为 Tc 提供了更高的相关指数，而在下午提供了第二个方向。在大多数测量条件下，以气温加五度为干参考温度计算的应力指数与SC具有较高的相关性。