Feasibility of using pyranometers for continuous estimation of ground cover fraction in table grape vineyards

Abstract

This paper evaluates the feasibility of using pyranometers for continuous estimation of ground cover fraction (GCF) at remote, unattended sites. Photographical techniques were used for measuring GCF (GCFref) at a table grape vineyard grown under a net. Daily pyranometer-driven GCF estimates (GCFpyr) were obtained from solar radiation measurements above and below the canopy. For GCFpyr computation, solar radiation was averaged for two hours around solar noon (midday periods) and for daylight periods (8:00 to 18:00 Universal Time Coordinated). GCFpyr and GCFref (daylight periods) showed a good agreement: mean estimation error, 0.000; root mean square error, 0.113; index of agreement, 0.967. The high GCF attained, the large measurement range for GCF and the presence of the net above the table grape were the likely reasons for the good performance of GCFpyr in this crop despite the short number of pyranometers used. Further research is required to develop more appropriate calibration equations of GCFpyr and for a more detailed evaluation of using a short number of pyranometers to estimate GCF.