Determining Near-Surface Soil Heat Flux Density Using the Gradient Method: A Thermal Conductivity Model–Based Approach

AbstractIn the gradient method, soil heat flux density at a known depth G is determined as the product of soil thermal conductivity λ and temperature T gradient. While measuring λ in situ is difficult, many field studies readily support continuous, long-term monitoring of soil T and water content θ in the vadose zone. In this study, the performance of the gradient method is evaluated for estimating near-surface G using modeled λ and measured T. Hourly λ was estimated using a model that related λ to θ, soil bulk density ρb, and texture at 2-, 6-, and 10-cm depths. Soil heat flux Gm was estimated from modeled λ and measured T gradient (from thermocouples). The Gm results were evaluated with heat flux data GHP determined using independent measured λ and T gradient from heat-pulse probes. The λ model performed well at the three depths with 3.3%–7.4% errors. The Gm estimates were similar to GHP (agreed to within 15.1%), with the poorest agreement at the 2-cm soil depth, which was caused mainly by the relativel...

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