28 Jul 2025

Predicting Frozen Ground and Thaw Risk from Standard Land Model Output: Data, Algorithms, and GeoWATCH Implementation

Abstract: The Geospatial Weather Affected Terrain Conditions and Hazards (GeoWATCH) tool provides real-time mobility predictions at 30 m resolution on demand for any location on the globe. This tool combines dynamic weather data provided by the Air Force 557 Weather Wing (557WW) with static terrain data to downscale soil moisture from global and regional scales to resolutions better suited for terrain analysis applications. Frozen and thawing ground data layers were recently incorporated into the GeoWATCH framework to better support terrain assessment for Warfighter functions in cold regions. This report documents our approach for diagnosing the frozen and thawing ground data layers and provides examples. First, using data from controlled land-surface model simulations, we established simple curve-fitting formulas relating soil temperature to frozen water content. We then added the new formulas to the GeoWATCH code so that end users can generate frozen soil products on demand. Finally, GeoWATCH uses the resultant frozen soil product with a series of soil layers to determine the risk of actively thawing soil and springtime mud conditions. While the new overlays are not integrated into the GeoWATCH mobility diagnostic calculations, they provide insight into soil state conditions critical for operations and weather-based risk assessment in cold regions.

22 Apr 2024

Experimental and Numerical Analyses of Soil Electrical Resistivity under Subfreezing Conditions

Abstract: The engineering behavior of frozen soils is critical to the serviceability of civil infrastructure in cold regions. Among various geophysical techniques, electrical resistivity imaging is a promising technique that is cost effective and provides spatially continuous subsurface information. In this study, under freeze–thaw conditions, we carry out lab–scale 1D electrical resistivity measurements on frost–susceptible soils with varying water content and bulk density properties. We use a portable electrical resistivity meter for temporal electrical resistivity measurements and thermocouples for temperature monitoring. Dynamic temperature-dependent soil properties, most notably unfrozen water content, exert significant influences on the observed electrical resistivity. Below 0 ◦C, soil resistivity increases with the decreasing temperature. We also observe a hysteresis effect on the evolution of electrical resistivity during the freeze–thaw cycle, which effect we characterize with a sigmoidal model. At the same temperature, electrical resistivity during freezing is consistently lower than that during thawing. We have implemented this sigmoidal model into a COMSOL finite element model at both laboratory and field scales which enables the simulation of soil electrical resistivity response under both short–term and long–term sub–freezing conditions. Atmospheric temperature variations induce soil temperature change, and thereby phase transition and electrical resistivity change, with the rate of change being a function of the depth of investigation and soil properties include initial water content and initial temperature. This study advances the fundamental understanding of the electrical behaviors of frozen soils and enhance the application of electrical geophysical investigations in cold regions.