Infrared images of heat fields around a linear heater in tree trunks: what can be learned about sap flow measurement?

摘要

This contribution aims at improving the understanding of sap flow measurements in trees. Infrared heat field images taken around heating needles in sap transporting tree trunks are characterized by isotherms of elliptic shape with the heating needle in the lower focus. Increasing sap flow increases the eccentricity of the elliptic heat field. This dynamics of ellipses provides a simplified experimental-mathematical approach for the understanding and evaluation of the otherwise very complicated heat transfer- and distribution-problem involved. The results obtained are used to discuss criteria for possible improved positioning patterns for needle sensors aimed for sap flow calculation using the dynamics of ellipses.