Electrical resistivity tomography (ERT) measurements were collected by the U.S. Geological Survey (USGS) at two sites in Interior Alaska in September 2019 for the purposes of imaging permafrost structure and quantifying variations in subsurface moisture content in relation to thaw features. First, ERT data were collected at Big Trail Lake, a thermokarst lake outside of Fairbanks, Alaska, to quantify permafrost characteristics beneath the lake and across its shorelines. Three 222 m ERT survey lines were collected perpendicular to the North, East, and South shorelines, and two 110 m lines were collected parallel to the southeast and northeast shorelines. Models of electrical resistivity produced from these data revealed the distribution of frozen and thawed soil to depths of 10-40 m below the surface. Second, an ERT survey was conducted at Bonanza Creek LTER (Long Term Ecological Research), approximately 30 km southwest of Fairbanks, Alaska. This survey was a repeat of a previous ERT survey done in the same exact location in late August 2016, those data and models can be found here. The new survey line was 125 m in length and spanned the transition between burned and unburned forest. Models of electrical resistivity for this site imaged the structure of frozen and thawed soils to depths of 10-15 m. At both sites, manual permafrost-probe measurements of thaw depths were collected at set intervals along each ERT transect and used for comparison to the resistivity models.

Geophysical measurements were collected by the U.S. Geological Survey (USGS) at five sites in Interior Alaska in September 2021 for the purposes of imaging permafrost structure and quantifying variations in subsurface moisture content in relation to thaw features. Electrical resistivity tomography (ERT) measurements were made along transects 110-222 meters (m) in length to quantify subsurface permafrost characteristics. ERT transects were collected across a fireline boundary within the Bonanza Creek Long Term Ecological Research (LTER) site where repeat measurements have been made since 2014; across and adjacent to two thermokarst lakes, Vault Lake and Goldstream Lake; and along two profiles at the North Star golf course in Fairbanks, Alaska. Models of electrical resistivity produced from these data revealed the distribution of frozen and thawed soil to depths of 10-40 m below the surface. Borehole nuclear magnetic resonance (NMR) data were collected at two sites in order to determine liquid water content at depth in shallow boreholes. NMR data were collected in a 2.25 m-deep borehole at the North Star golf course adjacent to one of the ERT profiles, and in another two 1.625 m-deep boreholes adjacent to Big Trail Lake where previous NMR measurements were made in 2019 and 2020. Manual permafrost-probe measurements of thaw depths were collected at set intervals along each ERT transect and adjacent to NMR measurement locations used for comparison to the geophysical measurements, except at the North Star golf course where shallow permafrost was absent.

Geophysical measurements and related field data were collected by the U.S. Geological Survey (USGS) at the Alaska Peatland Experiment (APEX) site in Interior Alaska from 2018 to 2020 to characterize subsurface thermal and hydrologic conditions along a permafrost thaw gradient. The APEX site is managed by the Bonanza Creek LTER (Long Term Ecological Research). In April 2018, seven boreholes were emplaced to depths of 2.3-2.5 meters (m) to allow for repeat logging with downhole nuclear magnetic resonance (NMR) to quantify the spatial and temporal variations in unfrozen water content within active-layer and permafrost soils. NMR data were collected on ten separate occasions between April 2018 and October 2020. In June 2018, soil temperature and moisture sensors were installed at select locations and depths across the study site to record point-scale temperature and moisture conditions in 30 minute intervals. In August 2018, electrical resistivity tomography (ERT) data were collected along four 82 m-long transects. Models of electrical resistivity produced from these data revealed the spatial variability in soil lithology and thermal state (frozen vs. thawed) to depths up to 10-15 m below the surface. Lastly, manual permafrost-probe measurements of thaw depths were collected at each instrument location during summer site visits for comparison to the geophysical data.

Geophysical measurements were collected by the U.S. Geological Survey (USGS) at two sites in Interior Alaska in 2019 and 2020 for the purposes of imaging permafrost structure and quantifying variations in subsurface moisture content in relation to thaw features. In September 2019, electrical resistivity tomography (ERT) and downhole nuclear magnetic resonance (NMR) data were used to quantify permafrost characteristics across the shorelines of Big Trail Lake, a thermokarst lake outside of Fairbanks, Alaska. Three 222 m ERT survey lines were collected perpendicular to the North, East, and South shorelines, and two 110 m lines were collected parallel to the southeast and northeast shorelines. Models of electrical resistivity produced from these data revealed the distribution of frozen and thawed soil to depths of 10-40 m below the surface. NMR data were collected within two 2.3 m deep boreholes adjacent to the East and North perpendicular ERT survey lines in September 2019 and logged again in March 2020. Additional one-time NMR measurements of liquid water content were collected in September 2019 within the lakebed sediments (0-25 cm depth) in approximately 2.5 m lateral increments moving away from the shorelines in the East and North, between 0 and 12 m from shore. These NMR transects roughly coincided with the perpendicular ERT lines. A separate ERT survey was conducted at the Bonanza Creek LTER (Long Term Ecological Research) in September 2019 and was a repeat of a previous ERT survey done in the same exact location three years prior. The survey line was 125 m in length and spanned the transition between burned and unburned forest. Models of electrical resistivity for this site imaged the structure of frozen and thawed soils to depths of 10-15 m. At both sites, manual permafrost-probe measurements of thaw depths were collected at set intervals along each ERT transect and used for comparison to the resistivity models.

Geophysical measurements were collected by the U.S. Geological Survey (USGS) at five sites in Interior Alaska in September 2021 for the purposes of imaging permafrost structure and quantifying variations in subsurface moisture content in relation to thaw features. Borehole nuclear magnetic resonance (NMR) data were collected at two sites in order to determine liquid water content at depth in shallow boreholes. NMR data were collected in a 2.25 m-deep borehole at the North Star golf course adjacent to one of the ERT profiles, and in another two 1.625 m-deep boreholes adjacent to Big Trail Lake where previous NMR measurements were made in 2019 and 2020.

Electrical resistivity tomography (ERT), downhole nuclear magnetic resonance (NMR), and manual permafrost-probe measurements were used to quantify permafrost characteristics along transects within several catchments in interior Alaska in late summer 2016 and 2017. Geophysical sites were chosen to coincide with additional soil, hydrologic, and geochemical measurements adjacent to various low-order streams and tributaries in a mix of burned and unburned watersheds in both silty and rocky environments. Data were collected in support of the Striegl-01 NASA ABoVE project, "Vulnerability of inland waters and the aquatic carbon cycle to changing permafrost and climate across boreal northwestern North America." Additional geophysical measurements were conducted at the Bonanza Creek LTER and at a thermokarst bog site. ERT transects were 100 - 200 m in length, and produce models of electrical resistivity structure to depths of 10 - 15 m that indicate the distribution of frozen ground with high spatial resolution. Manual permafrost-probe measurements were made periodically along ERT transects to validate the depth to the top of permafrost. Downhole NMR measurements were made at select locations near the ERT transects to quantify in situ unfrozen water content and to help constrain interpretations of electrical resistivity models.

Electrical resistivity tomography (ERT), downhole nuclear magnetic resonance (NMR), and manual permafrost-probe measurements were used to quantify permafrost characteristics along transects within several catchments in interior Alaska in late summer 2016 and 2017. Geophysical sites were chosen to coincide with additional soil, hydrologic, and geochemical measurements adjacent to various low-order streams and tributaries in a mix of burned and unburned watersheds in both silty and rocky environments. Data were collected in support of the Striegl-01 NASA ABoVE project, "Vulnerability of inland waters and the aquatic carbon cycle to changing permafrost and climate across boreal northwestern North America." Additional geophysical measurements were conducted at the Bonanza Creek LTER and at a thermokarst bog site. ERT transects were 100 - 200 m in length, and produce models of electrical resistivity structure to depths of 10 - 15 m that indicate the distribution of frozen ground with high spatial resolution. Manual permafrost-probe measurements were made periodically along ERT transects to validate the depth to the top of permafrost. Downhole NMR measurements were made at select locations near the ERT transects to quantify in situ unfrozen water content and to help constrain interpretations of electrical resistivity models.