Two-Story Equations of Transmission of Solar Energy (TSETSE) in open boreal conifer tree stands

This paper presents the two-story equations of transmission of solar energy (TSETSE) model aimed to mimic the directional signature of the transmittan ce measured beneath conifer tree stands which form a highly clumped and dis continuous medium. The architecture of such tree species affect the radiati on distribution at the forest floor in providing interesting problems for r adiation process modeling. A tree is sketched by a conic-shaped crown layin g above a very thin trunk. The model contains a geometrical component to ac count for the between-crown gap probability and a volume component to descr ibe the radiative transfer within a single crown which is here assimilated to a turbid phytomedium. The diurnal pattern of the simulated transmittance at a local point between trees yields peaks of the radiation loading at th e understory as a function of tree arrangement and whorl structure. The pra ctical aspect of the inversion method is achieved in several steps and rest s on the location of these radiation peaks, standing for the originality of this work. Once calibrated upon oblique measurements of the radiation pene tration, TSETSE allows for a retrieval of the tree distance, dimensions of the crown, and leaf area index.