中文摘要：

为了提高玉米冠层半球方向亮温（DBT）测量的准确性，对一套由工业用起重机平台和热红外成像仪组成的地面观测系统的四种测量方法进行了对比和评价。这些方法基于不同的测量原理：（1）通过移动起重机和平台，从不同的角度去测量一个样区的DBT；（2）固定起重机和平台的位置，通过旋转热像仪，从不同的区域收集不同角度的DBT；（3）对方法2的改进，转动热像仪朝向的同时，吊车沿作物垄行方向运动，得到大区域内平均的DBT；（4）当热像仪沿着垂直于垄行方向的起重机臂运动时，用高成像频率对目标热辐射进行采样。在对这些方法进行比较时，着重考虑了玉米冠层亮温分布的时间和空间变化所产生的影响，对本观测系统的优点和局限性进行了初步探讨。最后，本文从实际应用的角度，提出了一个基于这个系统且优化了的DBT测量方法。

英文摘要：

In this study, a recent crane based thermal camera system developed by INRA-Avignon of France is presented, and then four measuring methods for hemispherical directional brightness temperature （DBT） observations are introduced. These methods are based on different measurement principles： （1） view the same surface from different angle by moving the crane and platform to assure the sensor always toward the target; （2） view different part of the field to collect DBT of different angles by means of rotating the camera to different directions instead of moving the camera; （ 3 ） view different part of the field by moving the camera along the row direction; and （4） scan the field with a high imaging frequency while the camera moves along the crane bar vertical to the row direction. During the comparison of these methods, special emphasis is on the analysis of temporal and spatial variations of maize canopy brightness temperature distribution, from which the main errors of these methods are analyzed. The study also presents common shortcomings and limitation of the field observations with this system. At last, recommendations for optimal field measurement of hemispherical DBT with the system are given from an application-oriented viewpoint.