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Sensors 2016, 16(12), 2042; doi:10.3390/s16122042

Comparing ∆Tmax Determination Approaches for Granier-Based Sapflow Estimations

1
Department of Geography, University of Bonn, Meckenheimer Allee 166, 53115 Bonn, Germany
2
Center for Development Research, University of Bonn, Walter-Flex-Straße 3, 53113 Bonn, Germany
3
Dendro-Labor Windeck, Tree-Ring Analytics, 51570 Windeck, Germany
*
Author to whom correspondence should be addressed.
Academic Editor: Russell Binions
Received: 19 October 2016 / Revised: 22 November 2016 / Accepted: 28 November 2016 / Published: 1 December 2016
(This article belongs to the Special Issue Sensors for Environmental Monitoring 2016)
View Full-Text   |   Download PDF [3497 KB, uploaded 1 December 2016]   |  

Abstract

Granier-type thermal dissipation probes are common instruments for quantifying tree water use in forest hydrological studies. Estimating sapflow using Granier-type sapflow sensors requires determining the maximum temperature gradient (∆Tmax) between the heated probe and the reference probe below. ∆Tmax represents a state of zero sap flux, which was originally assumed to occur each night leading to a ∆Tmax determination on a daily basis. However, researchers have proven that, under certain conditions, sapflow may continue throughout the night. Therefore alternative approaches to determining ∆Tmax have been developed. Multiple ∆Tmax approaches are now in use; however, sapflow estimates remain imprecise because the empirical equation that transfers the raw temperature signal (∆T) to sap flux density (Fd) is strongly sensitive to ∆Tmax. In this study, we analyze the effects of different ∆Tmax determination approaches on sub-daily, daily and (intra-)seasonal Fd estimations. On this basis, we quantify the uncertainty of sapflow calculations, which is related to the raw signal processing. We show that the ∆Tmax determination procedure has a major influence on absolute ∆Tmax values and the respective sap flux density computations. Consequently, the choice of the ∆Tmax determination approach may be a significant source of uncertainty in sapflow estimations. View Full-Text
Keywords: heat dissipation; thermal dissipation; maximum temperature gradient; data processing; transpiration; Norway spruce; Picea abies heat dissipation; thermal dissipation; maximum temperature gradient; data processing; transpiration; Norway spruce; Picea abies
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Rabbel, I.; Diekkrüger, B.; Voigt, H.; Neuwirth, B. Comparing ∆Tmax Determination Approaches for Granier-Based Sapflow Estimations. Sensors 2016, 16, 2042.

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