Exploring the Soil Heat Flux Time Lag using Numerical Simulation and Measurements
Location
Logan Country Club
Start Date
3-28-2017 3:10 PM
End Date
3-28-2017 3:15 PM
Description
Surface energy balance is an important tool for sustainable water management and for estimating crop evapotranspiration. Net radiation is converted to latent heat flux, sensible heat flux, and soil heat flux at the surface of the earth. The soil heat flux component is challenging to determine because of the high degree of variation in soil moisture and temperature within the soil profile. Surface soil heat flux may be approximated using atmospheric and solar data but is more readily determined using soil heat flux measurements, which are typically made at a reference soil depth of 8 cm. However, the surface soil heat flux occurring at any moment in time is actually not measured at the reference depth until some time later because of the travel time for that heat to reach the heat flux plate 8 cm below. This means there is generally a time lag in the soil heat flux measurement relative to the atmospheric measurements. Consideration of the time lag between the soil surface and the sub-surface could improve the accuracy of energy balance calculations. Accurate soil surface heat flux estimation is crucial for modeling of energy and water-related processes as well as for validating sensor-based ET measurement techniques. Numerical models have been developed to simulate both soil-heat and -water dynamics. The objectives of this study were to estimate surface soil heat flux based on atmospheric data and soil heat flux measurements in the field and to investigate the soil heat flux time lag using the HYRDUS-1D model. Atmospheric data were collected from an Eddie covariance tower in a vineyard, including evapotranspiration, net radiation, air temperature and humidity, and wind speed. Soil moisture was measured using a Hydra Probe and soil heat flux was measured at 1.5- and 8-cm with Tri-needle heat pulse probes. Preliminary results indicated a 2-3 hour time lag for soil heat flux measurements in saturated soil between 1.5 and 8 cm depth. Estimates of soil heat flux time lag between the surface and 8 cm depth and the likely causes of the delay will be presented.
Exploring the Soil Heat Flux Time Lag using Numerical Simulation and Measurements
Logan Country Club
Surface energy balance is an important tool for sustainable water management and for estimating crop evapotranspiration. Net radiation is converted to latent heat flux, sensible heat flux, and soil heat flux at the surface of the earth. The soil heat flux component is challenging to determine because of the high degree of variation in soil moisture and temperature within the soil profile. Surface soil heat flux may be approximated using atmospheric and solar data but is more readily determined using soil heat flux measurements, which are typically made at a reference soil depth of 8 cm. However, the surface soil heat flux occurring at any moment in time is actually not measured at the reference depth until some time later because of the travel time for that heat to reach the heat flux plate 8 cm below. This means there is generally a time lag in the soil heat flux measurement relative to the atmospheric measurements. Consideration of the time lag between the soil surface and the sub-surface could improve the accuracy of energy balance calculations. Accurate soil surface heat flux estimation is crucial for modeling of energy and water-related processes as well as for validating sensor-based ET measurement techniques. Numerical models have been developed to simulate both soil-heat and -water dynamics. The objectives of this study were to estimate surface soil heat flux based on atmospheric data and soil heat flux measurements in the field and to investigate the soil heat flux time lag using the HYRDUS-1D model. Atmospheric data were collected from an Eddie covariance tower in a vineyard, including evapotranspiration, net radiation, air temperature and humidity, and wind speed. Soil moisture was measured using a Hydra Probe and soil heat flux was measured at 1.5- and 8-cm with Tri-needle heat pulse probes. Preliminary results indicated a 2-3 hour time lag for soil heat flux measurements in saturated soil between 1.5 and 8 cm depth. Estimates of soil heat flux time lag between the surface and 8 cm depth and the likely causes of the delay will be presented.