Comparing L-band Radiometry and in Situ Permittivity at 50 MHz of Agricultural Soils During a Freeze/Thaw Validation Campaign
Abstract
Up to a third of Earth's land surface experiences a transition between seasonally thawed conditions, like the surface of permafrost's active layer, or seasonally frozen conditions with even more regions experiencing short-term diurnal freeze/thaw (F/T) events. Freezing and thawing of the land surface plays an important role in local, regional and global weather and climate, affects the geotechnical properties of soil and slope stability, and influences critical processes such as the land surface energy balance, biogeochemical dynamics, and hydrological partitioning between surface runoff and infiltration. Although it is imperative, monitoring F/T state is difficult given its enormous extent and prevalence in places where access is limited, and climate is extreme. The most viable option at continental scales is through the use of microwave satellite observations. These observations must be validated against ground observations for accurate and credible usage. The SLAPEx F/T field campaign was conducted during the first two weeks of November 2015 to capture transient F/T events at various scales over agricultural land in Manitoba, Canada.
We compared the freeze/thaw (F/T) signatures acquired from the surface-based L-band radiometers and soil moisture/permittivity probes, employed for the SLAPEx campaign, with those from the supporting soil and meteorological instrument suite. A logistic growth model was fitted to the permittivity-temperature measurements to characterize soil moisture F/T events, and the freezing point depression. The model was adapted for use with brightness temperature measurements. Although only a few partial F/T events were detected during the field campaign, the freeze/thaw signatures exhibit coherent behavior. Results show that validating F/T products using ground temperature data, the temperature gradient at even relatively shallow depths (2.5, and 5 cm), can result in a bias in near-surface F/T status.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.H51S1751P
- Keywords:
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- 1843 Land/atmosphere interactions;
- HYDROLOGY;
- 1855 Remote sensing;
- HYDROLOGY;
- 1866 Soil moisture;
- HYDROLOGY;
- 4262 Ocean observing systems;
- OCEANOGRAPHY: GENERAL