Plot-scale assessment of soil freeze/thaw detection and variability with impedance probes: Egbert, Ontario [Canada] raw dataset

Several large in-situ soil moisture-monitoring networks currently exist over seasonally frozen regions which could have potential use for the validation of remote sensing soil freeze/thaw (F/T) products. However, due to our limited understanding of how the existing network instrumentation responds to changes in near surface soil F/T, these networks are largely ignored during the winter months. This case study describes the results of a small plot-scale (7 x7 m) study from November 2013 through April 2014 instrumented with 36 Hydra Probes. During the study, soil temperature and real dielectric permittivity were measured every 15 minutes during two F/T transition periods at shallow soil depths (0-10 cm). Categorical soil temperature and real dielectric permittivity techniques were then used to define the soil F/T state during these periods. The study showed that both methods for detecting soil freezing showed agreement (53.3- 60.9 %) during the spring thaw. Bootstrapping results demonstrated that both moderate to strong agreement with each other (84.7- 95.6 %) during the fall freeze but only weak techniques showed a mean difference within ±1.0°C and ±1.4 between the standard 5 cm below ground horizontal probe installation depth and the 2, 10 and integrated 0 -5.7 cm probe depths installed within the same study plot. Overall this study demonstrates that the Hydra Probe offers promise for near surface soil F/T detection using existing soil moisture monitoring networks. The research also suggests that the device may have important applications for the validation of remote sensing F/T products.