Leslie A. Morrissey, Gerald P. Livingston
Current global models project that climatic change over the next century may occur first and most dramatically affect northern high latitude ecosystems. Of particular concern is whether enhanced decomposition of soil organic materials will release additional greenhouse gases, e.g., CO2 and CH4, into the atmosphere and thus further enhance climatic warming. European Remote Sensing (ERS-1) satellite synthetic aperture radar (SAR) provides the first spaceborne SAR system for multi-year, multi-temporal assessment of high latitude ecosystems. ERS-1 SAR is particularly suited to the characterization of wetland and non-wetland areas which differentiate CH4 and CO2 source and sink areas. Analysis of ERS-1 C-band SAR data is underway to determine the type and extent of wetlands (methane source areas), the extent and timing of inundation (anaerobic substrates required for methane production), and vegetation community type and amount (methane transport pathway).
With the ultimate goal of assessing the contribution of northern ecosystems to the global methane budget, our initial research focused on making methane chamber-based measurements at sites in northern and central Alaska over the last several years. Our published results have shown that exchange rates for highly productive herbaceous fens are often 10-100 fold greater than other sources, such as bogs, and as much as 100-1000 fold greater than methane consuming areas, such as upland forests. Figure 1 is a schematic elevation cross-section showing average methane exchange rates (mg CH4 m-2 hr-1) for representative communities of central Alaska. More recent research activities have centered on the acquisition and analysis of ERS-1 SAR data for Barrow and Prudhoe Bay, Alaska, during the annual cycles of 1991 through 1993. Analysis of AIRSAR data (Figure 2) collected by the DC-8 aircraft over Minto Flats, Alaska, documents the successful discrimination of boreal vegetation communities as they relate to methane exchange. Our research has shown that backscatter for methane consuming upland deciduous and coniferous forests and tall shrubs were well separated from those of methane source areas Even within methane source areas, those communities with high exchange rates (i.e., fens; Figure 3 ) are separable from bogs and open water with low exchange rates (mg/m2/hr). Efforts to expand the geographic coverage of these SAR-derived wetland maps into Canada and Siberia are underway.
Other Interesting Images:
Methane flux image of the western North Slope of Alaska. .
Shuttle Imaging Radar (SIR-C) from space.
Pathways for methane transport from soil to atmosphere.
Ames-Moffett contact: Dr. Leslie A. Morrissey
or tel: (415) 604-3617
Headquarters program office: OMTPE