Study on the Lambertian property of cropland in thermal infrared region through field experiments

• Published in: 2016 Fifth International Conference on Agro-Geoinformatics (Agro-Geoinformatics) pp. 1 - 5
• Main Authors: Lili Tu, Jun Geng, Lechan Yang, Zhihao Qin, Wenjuan Li
• Format: Conference Proceeding
• Language: English
• Published: IEEE 01.07.2016
• Subjects: Cropland; Lambertian property; Ocean temperature; Radiant directionality; Remote sensing; Sea surface; Soil; Temperature measurement; Temperature sensors
• DOI: 10.1109/Agro-Geoinformatics.2016.7577645

The Lambertian surface has been a very important assumption in constructing the thermal radiance transfer equation for remote sensing of ground surface temperature. Crops are often planted in a row structure, and complex row architectures may lead to differences in terms of sunlight. Study of the radiation difference caused by observation directions for cropland is important for crop research by remote sensing technology. In this study, we studied the Lambertian property of cropland surfaces in the thermal infrared region through rigorous experiments in the field. Because a Lambertian surface has a homogeneous intensity of thermal emissions in hemispherical directions for a specific ground surface under specific kinetic temperature and emission conditions, we set up a series of field experiments to demonstrate the properties of the cropland. Three typical ground surfaces were selected for the experiments to observe thermal emissions: paddy field, bare soil and grass. Radiance thermometry was used to observe the ground emissions from 7 directions: 30°, 45°, 60°, 90°, 120°, 135° and 150°. The solar zenith angle was considered for the observation of ground emissions. Experiments were conducted at three different sites, both in daytime and nighttime, in Nanjing, China. Down-welling atmospheric emissions were considered for correction of the observed radiance to compute the ground surface radiance in the experiments. To determine whether different observation angles have significantly different effects on radiance, statistical analyses (ANOVA and Friedman test) were carried out. Post hoc multiple comparison tests and pairwise multiple comparisons were also conducted to inspect the various pairings of observation angles and to discover the radiance difference between them. According to the experiments and analysis of results, it can be concluded that the cropland does not have Lambertian characteristics in the thermal infrared region for thermal remote sensing. This means that both the thick vegetative canopy and the smooth bare soil have non-Lambertian properties. The results also indicated that 1) the radiance difference among the seven observation angles were larger in the daytime than at nighttime, and 2) the paddy field, bare soil and grass had their own characteristic differences in radiance among the different observation angles.