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Polarimetric ALOS Potential for Sub-arctic Peatland Wetland Characterization in Wapusk National Park

R. Touzi(1), R. Brook(2), A.M. Demers(1) and S. Kowalchuk(3)

(1) Canada Centre for Remote Sensing, 588 Booth St.,, Ottawa, Ontario, K1A 0Y7, Canada
(2) University of Calgary, 3330 Hospital Drive NW, Calgary, Alberta T2N 4N1, Canada
(3) PARKS CANADA, Box 127,, Churchill, MB R0B 0E0, Canada

Abstract

The Hudson Bay Lowlands contain the most extensive wetlands and thickest peat deposits in Canada. The region is home to unique concentrations of wildlife, most notably polar bears, caribou, and migratory birds. Bears rely on inland denning habitat, caribou are tied to peatland vegetation, and birds intensively graze coastal herbaceous salt marsh and fen. Major wetland transformations have been detected related to isostatic uplift [1], fire [2], and goose grazing [3]Climate change is expected to have important, though poorly understood, impacts on the peatland ecosystems of Wapusk National Park in the Hudson Bay Lowlands of Manitoba, which may include an increased rate and extent of fires, collapse of surficial permafrost, and drying of wetlands. While it is well established that fens change naturally into bogs over time and that bogs can revert to fens, the rate of these changes will likely be significantly altered by climate change and will have important implications for polar bear denning habitat which is entirely within bogs with thick peat deposits. Climate change is a major source of stress of Wapusk wetland that should affect gradually park’s fauna and flora biodiversity. Earth observation satellite and in particular all weather L-band polarimetric ALOS, should provide the required information for monitoring the impact of climate change on the integrity of the 11,475 km2 park.

In this study, several dual-polarization and fully polarimetric ALOS acquisitions are analyzed for the characterization of a peatland wetland site in Wapusk National Park in combination with extensive field collection of vegetation structure and diversity and measurements of permafrost active layer thickness. The Touzi decomposition [3], which has been recently introduced for a unique and roll-invariant characterization of target scattering, is investigated. In contrast to the Cloude-Pottier [4] decomposition, which uses a real entity to describe target scattering type, the Touzi decomposition characterizes uniquely the scattering type with a complex entity, whose both magnitude and phase have been shown very promising for wetland class characterization [5]. In particular, the new target scattering phase has been shown to be very promising for separation of nutrient poor fens from bogs. We would expect that this parameter should play a key role in monitoring the bog-fen transformation process related to climate change stress. All the Touzi decomposition parameters will be investigated, and the polarimetric ALOS capability for wetland characterization will be assessed with reference to in-situ ground measurements. Implications for the operational use of polarimetric L-band ALOS in conjunction with the C-band Radarsat2 for wetland monitoring are discussed.

References:

[1] R.K. Brook and N.C. Kenkel, “A multivariate approach to vegetation mapping of Manitoba’s Hudson Bay Lowlands”, International Journal of Remote Sensing, Vol. 23, pp. 4761-4776, 2002

[2] R.K. Brook, “Forest and tundra fires in the Hudson Bay Lowlands of Manitoba. IN: Climate Change: Linking Traditional and Scientific Knowledge”, eds R. Riewe & J. Oakes, Aboriginal Issues Press, Winnipeg, Manitoba, Canada, 2006.

[3] A. P. Jano, R. L. Jefferies and R. Rockwell, “The Detection of Vegetational Change by Multitemporal Analysis of LANDSAT Data: The Effects of Goose Foraging”, Journal of Ecology, Vol. 86, No. 1 (Feb., 1998), pp. 93-99

[4] Touzi, R., “Target Scattering Decomposition in Terms of Roll-Invariant Target Parameters ”, Proc. IEEE TGRS, Vol. 45, No. 1, Jan. 2007.

[5] R. Cloude and E. Pottier, “A review of target decomposition theorems in radar polarimetry”, IEEE Trans. Geoscience Rem. Sens., Vol. 34, No. 2, pp. 498-518, March 1996.

[6] R. Touzi, A. Deschamps and G. Rother, “Wetalnd characterization using polarimetric Radarsat-2 capability”, Can. J. Rem. Sens., Vol. 33, No. 1:S56–S67, 2007

 

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