Monitoring freeze-thaw transitions of the soil and vegetation inhigh latitude terrestrial ecosystems is useful for determining thelength of the growing season, and for monitoring potential damage toliving plants due to freezing and frost drought. The authors present atechnique for monitoring freeze-thaw cycles using repeat-pass SAR datafrom the European Remote Sensing Satellite, ERS-1, 100 km in swathwidth, and mosaicked together along a north-south Alaskan transect 1400km in length. Freezing of the soil and vegetation is detected based on a3 dB decrease in radar cross-section σ0 relative to aknown thawed state of the landscape. The decrease in σ0is explained by radar backscatter models as resulting from a largedecrease of the dielectric constant of the soil and vegetation withfreezing. The technique is validated using air-temperature recordingsfrom three forest stands along the Tanana River near Manley Hot Springs,and from local weather stations along the transect. The technique doesnot apply to areas of standing water, but is independent of the type ofvegetation cover, and permits the spatial and temporal monitoring offreezing of the natural landscape at the regional scale
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