Integrating geographic information systems and hemispherical photography in the assessment of canopy light profiles in a vineyard

The light conditions in a vineyard primarily depend on the latitude of the vineyard and day of the year. Based on these parameters, the exact daily Sun path can be calculated with astronomical functions. However, effective Sun hours also depend on the topography of the territory, both for direct and diffuse radiation, as a result of the presence of hills and mountains on the Sun path (direct radiation) or, in general, reducing the sky fraction (diffuse radiation). A 360° orographic profile can be assessed by topographic survey, by using hemispherical pictures or Geographic Information Systems (GIS) and Digital Elevation Models (DEM). Moreover, row orientation, vine spacing, trellis system and height, leaf area density, exposure side, etc. further affect the light micro-climate within the canopy and, particularly, at bunch level, which may have consequences for the temperature and composition of the berries. In the present work two grapevine row orientations (NS and EW) were used to integrate various tools (Photovoltaic Geographical Information System, Visual Basic functions for the calculation of solar position and radiation, and results from the processing of hemispherical pictures) into an Excel Worksheet, called “SunMask”, that can be used as a new multi-purpose tool to 1) quickly calculate both the astronomic and the topographic sunrise, sunset, and maximum potential day length, 2) evaluate the effect of row orientation and canopy dimensions on the transmittance of the direct solar beam at high temporal resolution and, finally, 3) separate the effect of topographic and canopy masks on the Sun hours under clear-sky conditions. By combining the different tools in SunMask, both the astronomic and topographic (as affected by the surrounding hills and mountains) sunrise, sunset, and maximum potential day length can be quickly and easily calculated for every specific vineyard terroir/location at any date or time in Europe, Africa and Asia. In addition, the software allows the evaluation of the effect of the canopy mask on the transmittance of the direct solar beam. SunMask will be a very important asset to improve information regarding radiation profiles of vineyards at meso- and micro-levels. It will be most valuable in the assessment of terroir suitability for vineyard establishment as well as for viticulture practice choices and the management of grapevine canopies.