A Direct Method for Estimating the Average Sap Flux Density Using a Modified Granier Measuring System

Abstract

The Granier sap flow measuring system that normally uses one analogue input channel of a datalogger for each sensor was modified to enable one channel to measure the average value of signals from two or more sensors. The sap flux density calculated from this average value of signals was very close (difference < 6.0%) to the arithmetic mean of the sap flux densities measured separately by means of individual sensors (using two or more input channels). The dynamics of the sap flux density measured by the modified method were similar to those measured by the original method. On a per-channel basis, the modified method reduced the ‘estimation error’ of sap flux density by 4–14-fold compared to the original method. By using the modified Granier system, the error in sap flow measurement that is usually associated with limited sampling can be substantially reduced without the need for extra dataloggers, the greatest item of expense.