A distributed temperature profiling system for vertically and laterally dense acquisition of soil and snow temperature

Baptiste Dafflon,John Fitzpatrick,John Peterson,Stijn Wielandt,Franklin H Akins,John Lamb,Sylvain Fiolleau,Carlotta Brunetti,Ian Shirley,Samuel Pullman,Sebastian Uhlemann,Robert Busey,Patrick Mcclure,Craig Ulrich,Chen Wang,Susan S Hubbard

doi:10.5194/tc-16-719-2022

Baptiste Dafflon, John Fitzpatrick + Show 14 more

Open Access

https://doi.org/10.5194/tc-16-719-2022

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Abstract

Abstract. Measuring soil and snow temperature with high vertical and lateral resolution is critical for advancing the predictive understanding of thermal and hydro-biogeochemical processes that govern the behavior of environmental systems. Vertically resolved soil temperature measurements enable the estimation of soil thermal regimes, frozen-/thawed-layer thickness, thermal parameters, and heat and/or water fluxes. Similarly, they can be used to capture the snow depth and the snowpack thermal parameters and fluxes. However, these measurements are challenging to acquire using conventional approaches due to their total cost, their limited vertical resolution, and their large installation footprint. This study presents the development and validation of a novel distributed temperature profiling (DTP) system that addresses these challenges. The system leverages digital temperature sensors to provide unprecedented, finely resolved depth profiles of temperature measurements with flexibility in system geometry and vertical resolution. The integrated miniaturized logger enables automated data acquisition, management, and wireless transfer. A novel calibration approach adapted to the DTP system confirms the factory-assured sensor accuracy of ±0.1 ∘C and enables improving it to ±0.015 ∘C. Numerical experiments indicate that, under normal environmental conditions, an additional error of 0.01 % in amplitude and 70 s time delay in amplitude for a diurnal period can be expected, owing to the DTP housing. We demonstrate the DTP systems capability at two field sites, one focused on understanding how snow dynamics influence mountainous water resources and the other focused on understanding how soil properties influence carbon cycling. Results indicate that the DTP system reliably captures the dynamics in snow depth and soil freezing and thawing depth, enabling advances in understanding the intensity and timing in surface processes and their impact on subsurface thermohydrological regimes. Overall, the DTP system fulfills the needs for data accuracy, minimal power consumption, and low total cost, enabling advances in the multiscale understanding of various cryospheric and hydro-biogeochemical processes.

Highlights

IntroductionTemperature is a key property for understanding and quantifying a multitude of processes occurring in and across the deep subsurface, soil, snow, vegetation, and atmosphere compartments of our Earth (e.g., Dingman, 2014; García et al, 2018)
We evaluate the value of the distributed temperature profiling (DTP) system to autonomously estimate snow depth, soil frozen, and thawed-layer thickness, as well as the possible probe upward displacement relative to soil surface that can occur in frost-susceptible soil using acquired temperature measurements
This study aimed at developing a low-power and smallfootprint DTP system providing vertically dense and highaccuracy temperature measurements at a total cost that would enable its deployment in a substantial number of locations, as needed, to improve the multiscale observation and understanding of environmental system functioning – in particular snowpack and soil thermal and hydrological dynamics

Summary

Introduction

Temperature is a key property for understanding and quantifying a multitude of processes occurring in and across the deep subsurface, soil, snow, vegetation, and atmosphere compartments of our Earth (e.g., Dingman, 2014; García et al, 2018). In addition to being a manifestation of thermal energy modulated by the heterogeneity of a given medium’s thermal parameters, temperature influences a myriad of above- and belowground processes, including aboveground biological dynamics, energy–water exchanges, subsurface heat and water fluxes, soil and root biogeochemical processes, and cryospheric processes (e.g., Chang et al, 2021; Davidson and Janssens, 2006; Jorgenson et al, 2010; Natali et al, 2019). The acquisition of time series of soil temperature data has been crucial for improving the understanding of a range of ecosystem properties and processes. Temperature time series have been used to explore the control that climate and subsurface properties have over permafrost dynamics (Brewer, 1958; Jorgenson et al, 2010), biogeochemical fluxes (Reichstein and Beer, 2008), plant function and root growth (Iversen et al, 2015), species and community distribution (Myers-Smith et al, 2011), and heat and water fluxes (Cable et al, 2014). Sequential acquisition of soil temperature down to a depth where thermal anomalies are larger than the effect of diurnal fluctuation has been done in volcanic and hydrothermal areas to delineate thermal anomalies and in some cases calculate ground fluxes (e.g., Hurwitz et al, 2012; Lubenow et al, 2016; Saba et al, 2007), as well as in discontinuous permafrost environments to identify near-surface permafrost (e.g., Léger et al, 2019)

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