| Summary: | The thermal behavior of tree trunks is currently only partially understood despite its great importance to forest productivity and climatic effects. From a remote sensing viewpoint, a better understanding of the relationship between the thermal regime of a tree and its thermal and microwave signal is necessary. The present study addresses two main questions: (1) How do tree trunk temperatures vary, spatially and temporally, in relation to different environmental factors. (2) How can observed thermal infrared radiations from the trunks describe these variations, and with which level of precision. In this study, measurements of internal temperatures (made with thermocouples), and of surface temperatures (made with thermographic images) of tree trunks under winter and summer conditions allowed us to describe the thermal behavior of trees. Results show that the radiant energy absorption can raise the surface and internal temperatures very rapidly and by several degrees above the ambiant air temperature. The temperature distribution tends to be highly asymmetric, with differences as large as 20ÀC between the hottest and coldest areas of the trunk.
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