Multi-scale Analysis of Inundation with Microwave and Optical Remote Sensing in the Amazon Basin: Applications to Biogeochemical Measurements and Modeling
John M. Melack -- Institute for Computational Earth System Science, University of California, Santa Barbara (UCSB)
Evlyn Marcia Leao de Moraes Novo -- Instituto Nacional de Pesquisas Espaciais (INPE) / DSR
We propose to conduct a multi-temporal, multi-scale, multi-sensor analysis of inundation and wetland vegetation in the Amazon basin that will be linked to biogeochemical measurement and modeling activities of LBA.
Our proposed remote sensing analyses will include optical (Landsat, AVHRR and EOS sensors), passive microwave (SMMR/SSMI) and active microwave (SIRC, JERS, ERS, and Radarsat) data to determine the temporally varying extent of inundation and associated vegetation. We will (1) provide synoptic, seasonal mapping of inundation and wetland vegetation structure for the Amazon basin; (2) incorporate the inundation and vegetation data into a GIS-based database; and (3) apply results from our analyses of wetland vegetation and inundation to related LBA studies of hydrological, ecological, and biogeochemical processes.
The expected time periods for recording an image useable for inundation analysis with the different remote sensing instruments we propose to employ varies from days to months. Based on an analysis of the spatial and temporal resolutions of the satellite sensors, we have determined that data fusion amongst the instruments will be critical to insure sufficient temporal coverage at the appropriate spatial scales. We anticipate that there will be an inundation-mapping limit for typical rivers with contributing drainage basins on the order of 1000-10,000 km2 when the flood conditions occur only for a week to a month. Individual sites may be mappable above and below this limit, depending on the local geomorphology and inundation hydrology.
We anticipate results of our analyses to be important for LBA activities associated with (1) methane and other trace gas emissions, (2) carbon dynamics of flooded forests, (3) land use on flood plains, (4) regional hydrologic modeling, and (6) detection of seasonal and inter-annual climate variability.
Implementation of our activities will be done as follows:
Optical sensing - The most effective technique for tracking the zone of river-water influence, in contrast to local-water influence, on wetland inundation is through the use of optical data of sufficiently fine resolution. We will modify our current method for suspended sediment analysis to incorporate data from the optical instruments expected during LBA, i.e., Landsat 7, MODIS, and AVHRR. The optical image analysis will be limited by access to sufficiently cloud and smoke-free data.
Active microwave sensors- We plan to use a multi-stage, hierarchical, rules-based approach to delineate floodplain inundation and vegetation using a decision-tree model which constructs a binary classification tree by recursively partitioning the training data into increasingly homogeneous subsets. Inundation mapping at a fine scale (12.5 m to 100 m pixel spacing) will be carried out using a combination of JERS (LHH), Radarsat (CHH), and ERS-2 (CVV) data. All these data will offer multi-temporal coverage of selected regions; only Radarsat's ScanSAR is expected to provide multi-temporal coverage of the whole Amazon basin during LBA.
Passive microwave sensors - Low-resolution sensors, such as the Scanning Multi-channel Microwave Radiometer (SMMR) and the Special Sensor Microwave Imager (SSMI), afford a synoptic view of the Amazon basin that complements finer-resolution SAR and optical data. We have developed linear mixing models that incorporate the observed microwave signature's major end members to estimate fractional inundation area. Data will be obtained as 0.25° x 0.25° grid cells, and modal values for each 2-week period will be used to determine inundation area
Field studies - Field surveys will be required at key LBA sites and selected wetlands to validate our classifications and maps. These surveys will entail low altitude videography and surface inspections from land and water. Geo-location of flight lines and surface sites will be done with portable GPS units. Further, we will use information obtained from the many hours of low altitude videography and field observations that we have collected previously, as well as from published literature and from personal contacts. To improve correlation between water levels and inundation extent in wetlands distant from major rivers or gauging stations on rivers, we will install automatic water level recorders.
During the first year, we will emphasize extension and validation of our microwave and optical classification algorithms and assembly of mutli-temporal data sets from ERS, Radarsat, JERS, Landsat and SSMI acquisitions. During the second and third years, we will emphasize production and distribution of inundation and wetland vegetation maps to relevant LBA projects and for our own complementary analyses.