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RESEARCH PRODUCT

Modelling solar radiation patterns for stand-scale studies in complex terrain

subject

description

International audience; A spatial model has been developed to simulate stand-scale patterns of irradiance over an hilly terrain bounded by a forest. Conceptually, the model is based on semi-empiric radiation equations and efficient viewshed algorithm further improved to account for sloping terrain and the presence of the forest. Model performance was assess on both radiometry and geometry. Comparison shows good agreement with observations. Model experiments were conducted for cloudy-less condition (i.e. at potential) along whole vegetative period of grapevine stand. Anal- ysis of deficit of irradiance for year 2003 shows that patterns are mainly due to the presence of the forest implying strong spatial gradient with cumulated deficit that reach value up to 2900MJ/m². Trends show more contrasted spatial than temporal behaviours with higher deficit located on the upper part of the stand. If close to forest, deficit is mainly due to direct component drop, low-lying part of the stand have direct component rapidly balanced (5m) by diffuse component. While for upper part the balance is only attained between 20m and 30m. The results demonstrate that the model is well-suited to analyse topoclimate on crop production.