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    Progress in Earth and Planetary Science

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    Ground subsidence and polygon development due to thermokarst in the Lena-Aldan interfluve, eastern Siberia, revealed by satellite remote sensing data

    Takahiro Abe, Yoshihiro IijimaTakahiro Abe, Yoshihiro Iijima

    Permafrost degradation, Thermokarst, Ice wedge polygon, Eastern Siberia, Interferometric synthetic aperture radar, Satellite optical images, Spatial frequency analysis

    (Left-top panels) Examples of WorldView panchromatic images indicating polygonal terrain in Mayya and Amga; (Left-bottom panel) Box plots of polygon density in the four towns. Median value of polygon density (M) and number of samples (N) are also shown in the figure; (Right-top panels) Examples of WorldView pansharpened images indicating well-developed and less-developed polygons; (Right-bottom panel) Averaged 1-D spectrum models of (red) well-developed, (blue) less-developed polygons, (yellow green) forested areas, and (cyan) water surface with the standard deviation (shaded areas). The dotted rectangle shows the range corresponding to the diameter of polygons (5-20 m).

    Thermokarst development is a topographic change in the landscape that is commonly associated with permafrost degradation in ice-rich permafrost regions. The Lena-Aldan interfluvial area in Central Yakutia in eastern Siberia has undergone extensive thermokarst development in the last three decades, particularly in the vicinity of settlements. Despite the negative effects of thermokarst development on the inhabitants of these settlements, no quantitative observation methods have been developed to investigate the surface displacement due to thermokarst development over entire towns. This study utilized interferometric synthetic aperture radar to reveal ground-surface displacement associated with thermokarst near the settlements of selected towns. The findings showed that significant subsidence was detected in disturbed areas (farming and abundant arable land) near the towns. The magnitude of subsidence in the Tyungyulyu and Mayya areas was less than that in Churapcha and Amga. Polygon density in a defined area in each town was examined using high-resolution optical images. The polygon density in Churapcha was considerably lower than that in Mayya, whereas polygonal texture in some areas in Tyungyulyu and Amga was unclear. Spatial frequency analysis using satellite optical images showed clear differences in averaged spectrum models between well-developed and less-developed polygons, which may reflect trough depths and density of vegetation between polygons. Satellite-based subsidence maps and statistics describing polygon development may be useful for evaluating both initial and subsequent stages of thermokarst development.