Validation of Permafrost Active Layer Estimates from Airborne SAR Observations

Abstract

In permafrost regions, active layer thickness (ALT) observations measure the effects of climate change and predict hydrologic and elemental cycling. Often, ALT is measured through direct ground-based measurements. Recently, synthetic aperture radar (SAR) measurements from airborne platforms have emerged as a method for observing seasonal thaw subsidence, soil moisture, and ALT in permafrost regions. This study validates airborne SAR-derived ALT estimates in three regions of Alaska, USA using calibrated ground penetrating radar (GPR) geophysical data. The remotely sensed ALT estimates matched the field observations within uncertainty for 79% of locations. The average uncertainty for the GPR-derived ALT validation dataset was 0.14 m while the average uncertainty for the SAR-derived ALT in pixels coincident with GPR data was 0.19 m. In the region near Utqiaġvik, the remotely sensed ALT appeared slightly larger than field observations while in the Yukon-Kuskokwim Delta region, the remotely sensed ALT appeared slightly smaller than field observations. In the northern foothills of the Brooks Range, near Toolik Lake, there was minimal bias between the field data and remotely sensed estimates. These findings suggest that airborne SAR-derived ALT estimates compare well with in situ probing and GPR, making SAR an effective tool to monitor permafrost measurements.

Permafrost Dynamics Observatory (PDO): 2. Joint Retrieval of Permafrost Active Layer Thickness and Soil Moisture From L‐Band InSAR and P‐Band PolSAR

“…Given that the soil moisture values in the Arctic tundra areas are relatively high (generally larger than 0.5 m 3 /m 3 ), the RMSE of 0.1 m 3 /m 3 is acceptable. As shown in Parsekian et al (2021), which provides further detailed comparisons between the PDO retrievals and GPR data, the biases in PDO ALT are negatively correlated to the biases of PDO soil moisture. Therefore, the negative biases observed in the PDO ALT retrievals against CALM ALT and GPR ALT are likely due to the overestimated soil moisture for those sites.…”

“…To compare the PDO ALT and soil moisture retrievals at the same spatial extent, the ALT and soil moisture estimated by ground‐penetrating radar (GPR) measurements in Yukon‐Kuskokwim (YK) Delta are used (Figure 9). Since the soil moisture estimated by GPR is the soil moisture averaged over the entire depth of the active layer (Clayton et al., 2021; Parsekian et al., 2021), the PDO retrieved soil moisture in Figure 9 is integrated along the active layer soil moisture profile up to thaw depth. When compared to GPR ALT, PDO ALT has a RMSE of 18 cm and a bias of −10 cm.…”

Tundra fire increases the likelihood of methane hotspot formation in the Yukon–Kuskokwim Delta, Alaska, USA

“…The flight lines were intentionally positioned to cover a chronosequence of tundra fire burn areas, including the large 2015 fires. The sampling strategy for ABoVE includes co-locating airborne measurements from multiple sensors, thus, the AVIRIS-NG data also overlap with the ABoVE airborne L-band synthetic aperture radar (SAR) acquisitions in the region (Miller et al 2019, Parsekian et al 2021; however, the SAR observations were not considered in this analysis. AVIRIS-NG radiance and reflectance data are available from the Oak Ridge Distributed Active Archive Center (Miller et al 2022).…”

A comprehensive approach to data collection, management, and visualization for terrain characterization in cold regions

“…Repeat measurements of ALT through time illustrate change and can inform terrain models that rely on active layer controls on various surface parameters. More recently, various remote detection methods have emerged for assessing ALT (i.e., Schaefer et al 2015;Parsekian et al 2021) but are beyond the current scope of this report.…”