InSAR Detection and Field Evidence for Thermokarst after a Tundra Wildfire, Using ALOS-PALSAR

Abstract

Abstract:Thermokarst is the process of ground subsidence caused by either the thawing of ice-rich permafrost or the melting of massive ground ice. The consequences of permafrost degradation associated with thermokarst for surface ecology, landscape evolution, and hydrological processes have been of great scientific interest and social concern. Part of a tundra patch affected by wildfire in northern Alaska (27.5 km 2 ) was investigated here, using remote sensing and in situ surveys to quantify and understand permafrost thaw dynamics after surface disturbances. A two-pass differential InSAR technique using L-band ALOS-PALSAR has been shown capable of capturing thermokarst subsidence triggered by a tundra fire at a spatial resolution of tens of meters, with supporting evidence from field data and optical satellite images. We have introduced a calibration procedure, comparing burned and unburned areas for InSAR subsidence signals, to remove the noise due to seasonal surface movement. In the first year after the fire, an average subsidence rate of 6.2 cm/year (vertical) was measured. Subsidence in the burned area continued over the following two years, with decreased rates. The mean rate of subsidence observed in our interferograms (from 24 July 2008 to 14 September 2010) was 3.3 cm/year, a value comparable to that estimated from field surveys at two plots on average (2.2 cm/year) for the six years after the fire. These results suggest that this InSAR-measured ground subsidence is caused by the development of thermokarst, a thawing process supported by surface change observations from high-resolution optical images and in situ ground level surveys.

Geomorphological and geochemistry changes in permafrost after the 2002 tundra wildfire in Kougarok, Seward Peninsula, Alaska

“…The annual mean rate (about 1 cm/year in this study) was slower than those found at the Anaktuvuk River Fire on the North Slope, Alaska [ Jones et al ., ; Iwahana et al ., ], or at the thermokarst site in Central Yakutia, Russia [ Fedorov et al ., ], as compared in Table . In the Anaktuvuk River Fire, rates increased from 2–3 cm/year in the first 3 years to over 6 cm/year in the following 5 years.…”

“…[], using airborne Laser Imaging Detection and Ranging (LiDAR), and by Iwahana et al . [], using spaceborne Interferometric Synthetic Aperture Radar (InSAR). However, these studies have had limited spatial or temporal resolution, and therefore there are needs to investigate thermokarst dynamics in various ice‐rich permafrost regions, in order to grasp overall trends of current thermokarst development.…”

“…In one study, a long-term change in surface heights at a disturbed larch forest in Eastern Siberia was measured in field surveys [Fedorov et al, 2014], for example. In another, remote sensing detection of thermokarst subsidence in burned areas of the Anaktuvuk River Fire [Jones et al, 2009] on the North Slope of Alaska-the largest tundra wildfire in the observation history-was performed by Jones et al [2015], using airborne Laser Imaging Detection and Ranging (LiDAR), and by Iwahana et al [2016], using spaceborne Interferometric Synthetic Aperture Radar (InSAR). However, these studies have had limited spatial or temporal resolution, and therefore there are needs to investigate thermokarst dynamics in various icerich permafrost regions, in order to grasp overall trends of current thermokarst development.…”

Vertical Velocities, Glacial Isostatic Adjustment, and Earth Structure of Northern and Western Alaska Based on Repeat GPS Measurements

“…This region is much less seismically or tectonically active than southern Alaska (Plafker and Berg, 1994). There is essentially no published information about vertical motions across Northern Alaska, outside of studies related to permafrost degradation (Iwahana et al, 2016;Jorgenson et al, 2006;Liljedahl et al, 2016;Liu et al, 2010;Osterkamp et al, 2009;Wang & Li, 1999).…”

Scattering Characteristics of X-, C- and L-Band PolSAR Data Examined for the Tundra Environment of the Tuktoyaktuk Peninsula, Canada

“…It was shown that X-, C-and L-Band data exhibit distinct scattering characteristics for the different land cover classes. Results indicate that the L-Band data were more sensitive to the bare ground classes; thus, it is better suited to investigate and monitor ground properties, e.g., soil moisture, or the surface heave and subsidence (via InSAR) caused by the freezing and thawing of the active layer (compare [17,20,21]); especially in sites dominated by shrubs. In contrast, use of short wavelengths (X-and C-Band) is beneficial for characterizing tundra and wetland vegetation.…”