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 July 2018, soil temperature and moisture sensors were installed at six out of the nine instrument locations (APEX1, APEX2, APEX3, APEX4, APEX7, APEX9). Thermistors (PS103J2, US Sensor, Orange, CA, USA) were placed at depths of 5, 30, 60, 120, and 180 centimeters (cm) with three replicates. Three sites (APEX1, APEX4, APEX9) contained an additional single 240 cm thermistor. Each soil temperature record was processed to remove erroneous values and spikes. Two time-domain reflectometry (TDR) probes (CS-616, Campbell Scientific, Logan UT, USA) were installed at the same six instrument sites to record soil moisture. The first TDR was inserted at a 45-degree angle down from the ground surface (0-20 cm), and the second from 20-40 cm. We applied an organic soils correction to the raw TDR data following the procedure in Bourgeau‐Chavez et al. (2010). Soil temperature and moisture data were recorded continuously from July 2018 through October 2020 on Campbell Scientific data loggers, with some data gaps due to power loss.

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). Nine instrument sites were established in April 2018 comprising a buried seismic station for continuous passive recording of the seismic wavefield, and seven of the nine sites were given a borehole for repeat nuclear magnetic resonance (NMR) logging. Between June 2018 and September 2019, measurements of active-layer thaw depth were regularly recorded at each of the nine instrument sites for comparison to the geophysical data. A nominal four measurements were collected in random azimuthal directions within 1 meter (m) distance of the buried seismometer at each instrument site. At sites containing an NMR borehole, an additional four to six measurements were taken within 1 m distance of the borehole location. During collection of electrical resistivity tomography (ERT) data in late August 2018, additional thaw depth measurements were collected at regular electrode intervals along each ERT survey line. Measurements were made with a 250 centimeter (cm) stainless-steel frost probe inserted to the depth of refusal.

This release contains Active Layer Thickness (ALT) and Organic Layer Thickness (OLT) measurements measured along transects in Alaska, 2015. Site condition information in terms of wildfire burns is also included.

This release contains Active Layer Thickness (ALT) and Organic Layer Thickness (OLT) measurements measured along transects in Alaska, 2015. Site condition information in terms of wildfire burns is also included.

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 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.

This dataset provides soil thaw depth and moisture measurements and dielectric properties measured by different research teams at sites in Alaska, U.S., and the Northwest Territories, Canada. There are multiple observations per site and 528,703 total observations. The dataset includes 223,230 observations of active layer thickness measured by mechanical probing (9.8%) or ground penetrating radar (GPR) (90.2%). Approximately 179,154 volumetric water content (VWC) measurements were collected using GPR (2.0%), HydroSense I and II probes (8.8%), in situ loggers (89.2%), and DualEM (<1.0%). Metadata includes the location, time, geospatial coordinates, sampling technique, measurement teams, and field team contact information. Measurements were typically collected in August and September near the end of the thaw season and cover the period from 2005 to 2022. This dataset, referred to as field measurements of Soil Moisture and Active layer Thickness (SMALT) (Schaefer et al., 2021), was developed for work in Clayton et al. (2021). It has been expanded in Version 2 to comprise a comprehensive dataset of NASA Arctic-Boreal Vulnerability Experiment (ABoVE) field campaign measurements of soil moisture and active layer thickness, including logger data of relevance to Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) acquisitions. The data are provided in comma separated values (CSV) format.

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.

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.