SMAP is one of four first-tier missions recommended by the National Research Council's Committee on Earth Science and Applications from Space (Earth Science and Applications from Space: National Imperatives for the Next Decade and Beyond, Space Studies Board, National Academies Press, 2007). SMAP data have both high science value and high applications value. The accuracy, resolution, and global coverage of SMAP soil moisture and freeze/thaw measurements are invaluable across many science and applications disciplines including hydrology, climate, carbon cycle, and the meteorological, environmental and ecology applications communities.

Future water resources are a critical societal impact of climate change, and scientific understanding of how such change may affect water supply and food production is crucial for policy makers. Current climate models uncertainties result in disagreement on whether there will be more or less water regionally compared to today; SMAP data will enable climate models to be brought into agreement on future trends in water resource availability. For these reasons, the Committees Water Resources Panel gave SMAP the highest mission priority within its field of interest.

Instrument

The SMAP instrument includes a radiometer and a synthetic aperture radar operating at L-band (1.20-1.41 GHz). The instrument is designed to make coincident measurements of surface emission and backscatter, with the ability to sense the soil conditions through moderate vegetation cover. The instrument measurements will be analyzed to yield estimates of soil moisture and freeze/thaw state. The antenna scan has a swath width of 1000 km providing global coverage within 3 days at the equator and 2 days at boreal latitudes (>45 degrees N).

Wetlands exert major impacts on global biogeochemistry, hydrology, and biological diversity. The extent and seasonal, interannual, and decadal variation of inundated wetland areas play key roles in ecosystem dynamics. Despite the importance of theseenvironments in the global cycling of carbon and water and to current and future climate, the extent and dynamics of global wetlands remain poorly characterized and modeled, primarily because of the scarcity of suitable regional-to-global remote sensing data for characterizing their distribution and dynamics.

The NASA Earth science project's main objective is the construction of a global-scale Earth System Data Record (ESDR) of inundated wetlands to facilitate investigations on their role in climate, biogeochemistry, hydrology, and biodiversity. The ESDR is comprised of two complementary components. The first component consists of fine-resolution, 100 meter, maps of wetland extent, vegetation type, and seasonal inundation dynamics, derived from Synthetic Aperture Radar (SAR) for continental-scale areas covering crucial wetland regions. The contemporary-era mapping will use newly available data (HH/HV) from the Phase Array L-Band SAR (PALSAR) sensor mounted on the Advanced Land Observing Satellite (ALOS). The second component is comprised of global monthly mappings of inundation extent at ~25 km resolution. These products will be derived from multiple satellite remote sensing observations including coarse resolution passive and active microwave sensors and optical data sets (e.g. ERS and SeaWindson-QuikSCAT scatterometers, AVHRR, MODIS) optimized specifically for inundation detection.

This ESDR will provide the first accurate, consistent and comprehensive global-scale data set of wetland inundation and vegetation, including continental-scale multi-temporal and multi-year monthly inundation dynamics at varying scales.

Approximately 68-80 percent of the North American region experiences seasonal freezing and thawing with the relative influence of these processes on terrestrial carbon budgets generally increasing at higher latitudes and elevations. The timing and duration of surface and soil freeze-thaw state is closely linked to vegetation phenology and growing season dynamics in northern temperate, sub-alpine, boreal and arctic biomes. Variability in these environmental variables also has been shown to have dramatic impacts on spatial patterns, seasonal to interannual variability and long-term trends in terrestrial carbon budgets and surface-atmosphere trace gas exchange primarily through biophysical controls on both photosynthesis and respiration. These processes are strongly influenced by land cover and soil properties, as well as the timing and condition of regional snow cover.

We are applying daily time series radar backscatter information from the SeaWinds Ku-band scatterometer to quantify spatial patterns and daily, seasonal and interannual variability in landscape freeze-thaw status in support of the North American Carbon Program (NACP). We are investigating synergistic relationships and trade-offs in relative sensitivity, spatial scale and temporal monitoring capabilities between SeaWinds freeze-thaw and MODIS land surface temperature (LST) products for quantifying landscape freeze-thaw state and thermal and moisture controls to vegetation gross primary production (GPP) and net primary production (NPP). We are quantifying the spatial and temporal patterns of these variables and determining their relative importance in determining seasonal patterns and annual variability in vegetation productivity using a modified form of the MODIS Production Efficiency Model (MOD17). We are also investigating relations between the microwave based freeze-thaw signal and surface biophysical network measures of the surface energy budget and associated linkages to soil respiration and land-atmosphere CO2 exchange dynamics. These results are being integrated within the larger NACP project to provide a comprehensive assessment of the North American carbon budget.

Map of the relative impact of low temperature on vegetation productivity for the North American study domain derived from the MODIS MOD17 time series. Darker blue regions denote areas where cold temperatures are a significant limitation to GPP, as determined from the MODIS LAI and FPAR time series (2000-2004) and MOD17 algorithm. Areas in white include non-vegetated surfaces and areas where low temperature is not a significant constraint to plant growth. Vegetation productivity over approximately 33% of Earth’s global vegetated surface is limited by cold temperatures and water in its frozen state. This investigation is characterizing the relative control of freeze-thaw state on the annual carbon budget of the North American domain.