Comparison of Grape Vineyard Linear-Soil Heat Flux and Soil Heat Pulse Probe Arrays.

Soil heat flux determination is important for reconciling the surface energy balance. Soil heat flux varies with sensing location and is greatly affected by vegetation orientation relative to solar position. Non-homogeneous vegetation such as vineyards and orchards are particularly challenging due to non-uniform shading effects. As part of the GRAPEX (Grape Remote sensing Atmospheric Profile and Evapotranspiration eXperiment) research project conducted in two Pinot Noir vineyards near Lodi CA, five soil heat flux plates (SHFP) were installed in a linear array between two grape vine rows spaced 3.35 m apart. This 5-SHFP system array was compared with a linear array of five soil heat pulse probes (SHPP), located adjacent to and at the same depth as the heat flux plate sensors. Each SHFP system was comprised of a Hydra Probe soil moisture sensor at a 5 cm depth, thermocouples at 2 and 6 cm depths and a soil heat flux plate at 8 cm. These paired arrays were located approximately 30 m west of an eddy covariance/flux tower system within each vineyard having different biomass/leaf area. We compared the minimum, maximum, average and range of soil heat flux based on each sensor array for better understanding the uncertainty in estimating soil heat flux from these two soil heat flux measurement systems. Implications on the effect of soil heat flux estimation on energy balance closure of the eddy covariance systems will be discussed.