Abstract
We present one of the first studies of the use of distributed temperature sensing (DTS) along fibre-optic cables to purposely monitor spatial and temporal variations in ground surface temperature (GST) and soil temperature, and provide an estimate of the heat flux at the base of the canopy layer and in the soil. Our field site was at a groundwater-fed wet meadow in the Netherlands covered by a canopy layer (between 0 and 0.5m thickness) consisting of grass and sedges. At this site, we ran a single cable across the surface in parallel 40m sections spaced by 2m, to create a 40m×40m monitoring field for GST. We also buried a short length (≈10m) of cable to depth of 0.1±0.02m to measure soil temperature. We monitored the temperature along the entire cable continuously over a two-day period and captured the diurnal course of GST, and how it was affected by rainfall and canopy structure. The diurnal GST range, as observed by the DTS system, varied between 20.94 and 35.08°C; precipitation events acted to suppress the range of GST. The spatial distribution of GST correlated with canopy vegetation height during both day and night. Using estimates of thermal inertia, combined with a harmonic analysis of GST and soil temperature, substrate- and soil-heat fluxes were determined. Our observations demonstrate how the use of DTS shows great promise in better characterizing area-average substrate/soil heat flux, their spatiotemporal variability, and how this variability is affected by canopy structure. The DTS system is able to provide a much richer data set than could be obtained from point temperature sensors. Furthermore, substrate heat fluxes derived from GST measurements may be able to provide improved closure of the land surface energy balance in micrometeorological field studies. This will enhance our understanding of how hydrometeorological processes interact with near-surface heat fluxes.
Highlights
We present one of the first studies of the use of Distributed Temperature Sensing (DTS) along fibre-optic cables to purposely monitor spatial and temporal variations in ground surface temperature (GST) and soil temperature, and provide an estimate of the heat flux at the base of the canopy layer and in the soil
The DTS technique illustrated here shows great promise in getting a better handle on area-average substrate and below-ground soil heat flux estimates, and their spatio-temporal variability, when the temperature mea442 surements are combined with a harmonic analysis and subsequent calculation 443 of soil heat flux with an analytical method (Verhoef, 2004)
Verhoef (2004) and van der Tol 449 (2012) have shown that the surface soil heat flux derived from soil temper450 atures, which requires a more complex analytical equation than Eq 1 that uses Ch and Dh explicitly, as well as the distance between the measurement location and the soil surface, is very sen454 sitive to errors in the assumed installation depth
Summary
Importance of the land surface thermal regime 3 The thermal regime at the land surface is the result of the interactions be tween vegetation, soil and atmosphere (e.g. transpiration, evaporation, soil 5 water-and heat transfer) These processes are affected by micro-topography, 6 local hydraulic and thermal properties, and radiative and structure param eters, such as canopy height and leaf area index (e.g. Moene and van Dam, 8 2014; Rodriguez-Iturbe et al, 1999). The energy balance describes how the net 11 radiation received at the land surface, Rn, is distributed between evapotran spiration (latent heat flux, LE), sensible heat flux, H, and substrate heat flux, Gsub The latter flux concerns heat that gets stored in (during the day) or released from (night-time) a substrate layer, consisting of topsoil and leaf-litter. As far as we are aware DTS has not been used for calculations of soil heat flux nor used to illustrate the implications of using a single measurement point as is practised widely in energy balance studies using a single heat flux plate (e.g. Wilson et al, 2002), to obtain soil heat flux for the determination of energy balance closure in heterogeneous canopies
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
