Abstract
Freezing and thawing of the land surface affects ecosystem and hydrological processes, the geotechnical properties of soil and slope stability. Currently, available datasets on land surface state lack either sufficient temporal or spatial resolution to adequately characterize the complexity of freeze/thaw transition period dynamics. Surface state changes can be detected using microwave remote sensing methods. Data available from scatterometer and Synthetic Aperture Radar (SAR) sensors have been used in the past in regional- to continental-scale approaches to monitor freeze/thaw transitions. This study aims to identify temporal and spatial patterns in freeze/thaw dynamics associated with the issue of differing temporal and spatial resolutions. For this purpose, two datasets representing the timing of freeze/thaw cycles at different resolutions and spatial extents were chosen. The used Advanced SCATterometer (ASCAT) Surface State Product offers daily circumpolar information from 2007–2013 for a 12.5-km grid. The SAR freeze/thaw product offers information of day of thawing and freezing for the years 2005–2010 with a nominal resolution of 500 m and a temporal resolution of up to twice per week. In order to assess the importance of scale when describing temporal and spatial patterns of freeze/thaw processes, the two datasets were compared for spring and autumn periods for the maximum number of overlapping years 2007–2010. The analysis revealed non-linear landscape specific relationships between the two scales, as well as distinct differences between the results for thawing and re-freezing periods. The results suggest that the integration of globally available high temporal resolution scatterometer data and higher spatial resolution SAR data could be a promising step towards monitoring surface state changes on a seasonal, as well as daily and circumpolar, as well as local scale.
Highlights
Permafrost and seasonal frost-related phenomena affect large parts of the Earth’s surface and are important variables in climate research
The general objective of this study was to explore these relationships for different landscape types and the representativity of coarse resolution scatterometer data for different permafrost environments
The Ob Estuary region acts as a good example for the importance of temporal resolution
Summary
Permafrost and seasonal frost-related phenomena affect large parts of the Earth’s surface and are important variables in climate research. This is especially true for Arctic areas where the ground surface undergoes a yearly freezing and thawing cycle. Freeze/thaw cycles are known to influence methane emissions [7] Their spatial extent, as well as changes in their dynamics have implications for hydrological applications, climate modeling and ecosystem processes [8], which occur at different scales. Regions underlain by permafrost are of special interest in this context as they have been shown to undergo rapid warming [9,10,11,12], and changes in ground stability have direct implications for roads, buildings and other forms of infrastructure [13]. Available datasets describing the freeze/thaw state of the ground surface lack either the adequate spatial or temporal resolution to describe these processes on a regional/local scale [14]
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