A NUMERICAL MODEL TO ESTIMATE THE RADIOMETRIC PERFORMANCE OF NET COVERED STRUCTURES (AGRONETS)

The design of structures to support nets for agricultural applications is mostly empirical. The radiometric behaviour of a net covered structure strongly depends on the shape of the structure, the postion of the sun and the external light conditions and the radiometric performance of net itself (Castellano et al. 2006). Nets are three-dimensional objects, the optical properties of nets can be different for different angles of incidence, the optical properties may change depending on the external light condictions (clear / overcast sky). The colour of the nets is important for the plant growth (Oren-Shamir et al. 2001). Transparent or semitransparent threads may be used for a high light level inside the net structure, green or black nets may be used for reducing excessive solar radiation and generate mild and more uniform internal light conditions. For these reasons, a light model is developed analysing the radiometric performance of a structure covered with nets. The radiometric properties of the permeable cladding measured will be used in this model for estimating the overall performance of the structure on crop level. The objectives of the use of a light model were: Estimating the year-round light interval of a net structure on plant level; Analysing the optical properties of different net structures during different seasons and different times of the day; Developing a simple method to estimate the optical properties of a net structure relevant for plant growth, use that as a tool for producers and growers.