Comparison of Four Measurement Methods for Acquiring Maize Hemispherical Directional Brightness Temperature with a Crane Based Thermal Camera System
采用热像仪测量玉米冠层半球方向亮温的四种方法比较

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.