HR: 0800h
AN: C31A-1118    [Abstracts]
TI: Regional Characterization of Landscape Freeze/Thaw Transitions Using Spaceborne Microwave Remote Sensing
AU: * Podest, E
EM: erika.podest@jpl.nasa.gov
AF: Jet Propulsion Laboratory/Caltech, 4800 Oak Grove Dr. Box 300-233, Pasadena, CA 91109 United States
AU: McDonald, K C
EM: kyle.mcdonald@jpl.nasa.gov
AF: Jet Propulsion Laboratory/Caltech, 4800 Oak Grove Dr. Box 300-233, Pasadena, CA 91109 United States
AU: Kimball, J S
EM: johnk@ntsg.umt.edu
AF: University of Montana, Flathead Lake Biological Station, 311 Biostation Ln., Polson, MT 59860 United States
AB: Boreal forests contain much of the Earth's terrestrial carbon storage in vegetation and 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 CO2 exchange with the atmosphere. 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 regardless of atmospheric conditions or solar illumination. We examined the spatial and temporal characteristics of the seasonal freeze/thaw transition across Alaska and Canada using time series spaceborne radar backscatter measurements from ERS (C-band, 100m, VV-polarization) and JERS (L-band, 100m, HH-polarization), and SeaWinds on QuikSCAT (Ku-band, 25km, HH and VV polarization) sensors. We examined remote sensing based freeze/thaw dynamics in relation to terrain, elevation and land cover complexity, and the relative effects of fire disturbance on these processes, as well as sensor frequency and spatial scale on sensor retrieval accuracy. All sensors examined were sensitive to landscape freeze/thaw state transitions, though sensitivity varies by sensor frequency and landscape component (e.g. vegetation, snow). The study regions analyzed exhibit high spatial heterogeneity in freeze/thaw dynamics associated with complex topography, surface water and land cover composition. Freeze/thaw spatial heterogeneity was detected at high (100m) resolution data. The backscatter freeze-thaw response was inversely proportional to elevation, with the seasonal thaw wave initiating at lower elevations and extending to higher elevations. The observed radar thaw signal also varied by aspect and land cover, with south-facing and deciduous forest sites thawing earlier relative to north-facing and coniferous forest sites. Relatively coarse resolution (25km) SeaWinds data provide for daily assessment of regional freeze/thaw state of the landscape. Ku-band is particularly responsive to areas dominated by snow where a small increase in snow wetness leads to a large drop in backscatter.
DE: 0704 Seasonally frozen ground
SC: Cryosphere [C]
MN: Fall Meeting 2005