PEATLAND SUBSURFACE WATER FLOW MONITORING USING POLARIMETRIC L-BAND PALSAR

摘要

The potential of L-band PALSAR for monitoring waterrnflow beneath the peat surface is demonstrated on a bog nearrnLac Saint Pierre (Canada). Two polarimetric ALOS acquisitionsrncollected at spring and fall under different water conditionsrnare used. The Touzi decomposition [1], which wasrnshown to be very promising for peatland characterizationrnusing the C-band Convair 580 SAR [2], is applied. Like inrn[2], the information provided by the multi-polarization (HH,rnHV, and VV), the scattering type magnitude (the Cloude αrnor the Touzi αs), the single scattering eigenvalues and thernentropy, cannot detect the presence of water underneath thernpeat surface. The Touzi scattering phase φ_(α_s) is shown tornbe the only target scattering decomposition parameter thatrncan detect water flow variations beneath the peat surface.rnThe fall acquisition that took place after two days rain permitsrndemonstrating that the wave can penetrate deep intornthe acrotelm layer to detect the rain water that has sinkedrnrapidly into the peat layer of high hydraulic conductivity.rnThe spring acquisition at dry conditions permits better discriminationrnof poor fen from bog. Similar performance havernbeen observed in a subarctic peatland in the Wapusk NationalrnPark using PALSAR data collected between June andrnSeptember 2010. While the multi-polarization informationrncould not detect any hydraulic changes in a sedge bulrushrnfen, φ_(α_s) can detect the peatland subsurface water level variationsrnbetween the June starting permafrost melting seasonrn(13 cm active layer) and the more advanced July meltingrnseasons (27 cm active layer). However, the scattering typernphase could not detect the water level change between Julyrnand August of more advanced melting conditions (activernlayer thickness of 60 cm). The L-band wave does not gornso deep into the fen to detect the presence of the subsurfacern(deeper than 27 cm) water.