

@mastersthesis {6889,
	title = {Monitoring boreal landscape freeze/thaw transitions with spaceborne microwave remote sensing},
	year = {2005},
	note = {U207713},
	school = {University of Dundee (United Kingdom)},
	type = {phdPh.{D}.},
	address = {Ann Arbor},
	abstract = {The landmass of the boreal high latitudes encompasses almost 30 percent of the global land area. Within these regions, a major portion of Earth{\textquoteright}s carbon is stored in vegetation and in seasonally frozen and permafrost soils. The annual freeze/thaw cycle drives the length of the growing season in these landscapes, and is a major factor determining annual productivity and associated exchange of CO2 with the atmosphere. Accurate characterisation of these processes can improve regional assessment of seasonal carbon dynamics. Satellite microwave remote sensing is sensitive to landscape freeze/thaw state and is an effective tool for this purpose since large inaccessible areas can be monitored on a temporal basis without limitations imposed by weather or daylight conditions. Variations in freeze/thaw processes are spatially and temporally complex due to topography, snow cover, land cover, fire disturbance, or local climatic conditions. This work examines the spatial and temporal characteristics of the seasonal freeze/thaw transition using time series spaceborne Synthetic Aperture Radar (SAR) imagery from ERS (C-band, 100 m, VV-polarisation) and JERS (L-band, 100 m, HH-polarisation), and scatterometer backscatter from QuikSCAT (Ku-band, 25 km, HH and VV polarisation). The analysis is focused over study sites in Alaska and Canada. In areas of complex terrain, freeze/thaw dynamics related to elevation, slope aspect, and varying land cover area are explored. In fire disturbance regions, the timing of the freeze/thaw transition is explored as related to a recovering landscape relative to that of a nearby control site. In areas of complex landscape distribution, differences in the freeze/thaw transition are examined according to individual land cover classes. The presence and status of snow cover and vegetation strongly influences accurate detection and monitoring of freeze/thaw status using microwave sensors. Radiative transfer backscatter modelling is employed to interpret snow and vegetation effects on the radar backscatter signatures as well as the sensitivity of different radar wavelengths to landscape component freeze/thaw processes. In situ biophysical measurements are used to validate results. Landscape freeze/thaw state maps are produced from the time series radar imagery and based on a temporal change discriminator. A scaling assessment is performed to determine the sub-grid spatial variability in freeze/thaw between the low-resolution 25 km scatterometer and the high resolution 100 m SAR. Results show that all sensors examined are sensitive to landscape freeze/thaw state transitions. Sensitivity to the transitions varies with landscape component (e.g. vegetation, snow) and sensor frequency. The study regions analysed exhibit a high spatial variability in freeze/thaw transition timing related to microclimate variations that arise from slope aspect, elevation, surface water, and land cover composition. These variations are observable at the high resolution, 100 m scale. At the coarser 25 km scale, however, the ability to resolve these patterns is less certain, particularly for topographically complex landscapes where elevation and slope/aspect effects can be considerable. Whereas the low-resolution 25 km measurements provide for daily assessment of landscape freeze/thaw state at coarse spatial scales, misclassification errors associated with landscape complexity should be considered when such information is employed to assess seasonal hydrologic and ecological processes in cold land regions.},
	keywords = {(UMI)AAIU207713, 0799:Remote sensing, Bibliographies, Earth sciences, Psychology{\textendash}Abstracting, Remote sensing, Statistics},
	url = {http://search.proquest.com/docview/301691364?accountid=14270},
	author = {Podest, E V}
}
