Abstract Thermal image quality is critical to accurately quantify spatial and temporal growth and stress patterns of field crops. Image data quality from a thermal sensor can be impacted by several factors including environment, flying altitude, and camera focal length. Often times the thermal sensor selection is based upon price or ease of availability for research. Metrics are available to select the flight altitude based on thermal sensor focal length for desired ground resolution, however, no study has been conducted to provide the relative difference in image data, quality and efficiency of generating a thermal orthomosaic. Therefore, this study was conducted with the goal to compare the accuracy of canopy temperature quantification and assess the quality of thermal orthomosaic when using a thermal sensor of different focal lengths and image acquisition at varying flying altitudes of an sUAS. Three thermal infrared cameras were selected with focal lengths of 9 mm, 13 mm, and 19 mm. All three cameras were flown at altitudes of 20 m, 50 m, and 80 m, to collect aerial imagery of a 7,000 m2 soybean field. The cameras were mounted on a rotary quadcopter. All flights were conducted at 3 m/s flying speed and 1 s shutter trigger interval. A ground reference system comprising of a panel and water bath system with measured actual temperature provided ground truth data for thermometric transformations. Imagery data were compared to assess differences in the number of images collected, percentage overlap required for 1 s shutter trigger interval, quality of orthomosaic and accuracy of canopy temperatures. Results showed that 13 mm focal length and 50 m altitude resulted in a finer resolution orthomosaic which can provide robust and accurate information on canopy temperature. The selection of such a system of camera lens angle and altitude can provide accurate, reliable and rapid canopy temperature quantification.

中文翻译：

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相机焦距和sUAS飞行高度对空间作物冠层温度评估的影响

摘要 热图像质量对于准确量化大田作物的时空生长和胁迫模式至关重要。来自热传感器的图像数据质量会受到多种因素的影响，包括环境、飞行高度和相机焦距。通常，热传感器的选择基于价格或研究的可用性。可以根据热传感器焦距为所需的地面分辨率选择飞行高度的度量标准，但是，尚未进行研究以提供图像数据、质量和生成热正射影像的效率的相对差异。所以，本研究旨在比较冠层温度量化的准确性并评估在 sUAS 的不同飞行高度下使用不同焦距的热传感器和图像采集时热正射影像的质量。选择了三个焦距分别为 9 mm、13 mm 和 19 mm 的热红外相机。所有三台相机都在 20 m、50 m 和 80 m 的海拔高度飞行，以收集 7,000 m2 大豆田的航拍图像。相机安装在旋转四轴飞行器上。所有飞行均以 3 m/s 的飞行速度和 1 s 的快门触发间隔进行。由面板和水浴系统组成的地面参考系统具有测量的实际温度，为测温变换提供了地面实况数据。比较图像数据以评估收集的图像数量的差异，1 秒快门触发间隔所需的重叠百分比、正射镶嵌质量和冠层温度的准确性。结果表明，13 mm 的焦距和 50 m 的高度产生了更精细的分辨率正射镶嵌，可以提供关于冠层温度的可靠和准确的信息。选择这样的摄像机镜头角度和高度系统可以提供准确、可靠和快速的冠层温度量化。