Working Towards an Independent Surface Renewal System without the Need for Calibration.

The surface renewal method estimates sensible heat flux density from high frequency temperature measurements. With this measure of sensible heat flux, latent heat flux can be estimated as a residual of the surface energy balance equation when net radiation and ground heat flux values are available. Surface renewal previously relied on calibration against other methods (e.g. Eddy Covariance) to obtain accurate measurements of sensible heat flux density. The calibration factor accounts for linear bias of the surface renewal measurements. The need for calibration limited the use of surface renewal to research applications. Recent studies have shown that compensating the frequency response characteristics of thermocouples converges the calibration factor near to the theoretically predicted values of 0.5.  This finding led to the development of an inexpensive, stand-alone surface renewal system to measure sensible heat flux without the need for calibration. We validated our new developments across numerous wine and table grape vineyards including a site containing a weighing lysimeter; the new method accurately reflected site water use in all sites. We developed a functional and commercially available system, and also discovered it can be used to detect stress signals from vineyards that could be used to trigger irrigation events. More research is needed to determine how well the system works over different crops and other varying factors. The new surface renewal method provides a potentially effective and low cost tool for use in irrigation management over multiple crops, geographical location, and environmental conditions without the need for calibration.