Error estimation in the acquisition of maize canopy hemispherical directional brightness temperature

A field experiment has been performed from May to August in 1999 over a maize canopy at INRA Avignon branch in south France. Directional brightness temperature (DBT) features were extracted from thermal infrared (TIR) images captured by a TIR camera mounted upon a crane platform. Different from the method with a goniometer, another approach based on the different principles has been developed that the camera can view different part of the field to collect DBT of different angles by means of rotating to different directions instead of moving the camera to make it always focus on a defined sample area. After the description of the measurement method, the evaluation of data acquisition is presented, where the quality and limits of this measurement method are discussed. In this study, a compromise is made in sampling design based on the analysis of canopy heterogeneity and FOV effect. An example of acquiring hemispherical DBT under natural conditions was given at last. In the analysis of the measurement at 13:10 of local time on June 24, 1999, the results showed the spatial heterogeneity of field thermal radiance played as the most important role. Using the new sampling method, the total error for acquiring hemispherical DBT was about 1.4degC in maximum with 95% confidence, when the amplitude of directional variation was larger than 7degC. The errors changed with measurement conditions, which made it different for each measurement