1. North American Carbon Program Sub-pixel Analysis of a 1-km Resolution Land-Water Mask Source of Data: The North American sub-pixel water mask product is derived from three data sets for three geographic extents:  North America (South of 60°N) – From the 1 arc-second (~30-m) resolution Shuttle Radar Topography Mission (SRTM) water body data set, the number of 1 arc-second pixels containing water within a 30 arc-second pixel were calculated to derive the sub pixel percentage of water (http://edc.usgs.gov/products/elevation/swbd.html).  Alaska (North of 60°N) – The National Land Cover Dataset (NLCD) 2001 is a land-cover classification scheme based on Landsat satellite data. This dataset is at a 30-m resolution and includes a water category. The water pixels from this land-cover data were used as input for the sub-pixel analysis (http://www.mrlc.gov/).  Canada (North of 60°N) – Hydrographic features from the National Topographic Data Base (NTDB) Maps were converted to 1 arc-second pixels, from which the number of 1 arc-second pixels containing water within a 30 arc-second pixel were calculated to derive the sub-pixel percentage of water (http://www.geogratis.ca/geogratis/en/collection/detail.do?id=8147). Introduction: The North American Carbon Program (NACP) is designed to quantify the magnitudes and distributions of carbon sources and sinks, explain the processes controlling them, and produce a consistent analysis of North America's carbon budget. The Modeling and Synthesis Thematic Data Center (MAST-DC) supports NACP by providing data products and data management services needed for modeling and synthesis activities. In many NACP or other project’s modeling activities, it is often necessary to mask or exclude regions in water. A land-water mask is a data layer that delineates regions in land and in water and is useful for this purpose. On a continental and global scale, a MODIS data based land-water mask is widely used and is one of the only products available for the whole of North America. This MODIS based land-water mask is at a resolution of 30 arc- seconds or approximately 1-km and delineates water features such as oceans, shoreline, lakes etc. A 250-m MODIS land-water mask is being developed, but may not be available for several years. Higher resolution water layers are available for North America, but the data are from different sources and hence are at different levels of accuracy (spatial and temporal). However, to take advantage of the fine resolution water data, we developed a 30 arc-second resolution map that captures sub-pixel information about land and water areas. The map contains the percentage of water within each 30 x 30- arc second pixel. This sub-pixel product will be useful as a water mask, and will also serve to understand the 30 arc-second MODIS based land-water mask product. Comparison of MODIS based Land-water mask and Sub-pixel Land-water mask for the Mid Continent Intensive (MCI) Region: Within shallow Inland Water (Inland Water <5-km from shore OR <50m deep), % containing more than 75% water = 74.5% % containing 50 - 75% water = 10.5% % containing 25 - 50% water = 6.9 % % containing less than 25% water = 8.1% Within Ocean Coastlines and Lake Shorelines (LAST land pixel) % containing more than 75% water = 8.7% % containing 50 - 75% water = 8.8% % containing 25 - 50% water = 13.1 % % containing less than 25% water = 69.4% Within Land % containing more than 75% water = 0.2% % containing 50 - 75% water = 0.4% % containing 25 - 50% water = 0.9 % % containing less than 25% water = 98.5% Environmental Sciences Division Oak Ridge National Laboratory Oak Ridge, TN 37830 *Latha Baskaran, Bob Cook and Suresh Kumar Santhana-Vannan The Shuttle Radar Topography Mission (SRTM) obtained elevation data on a near-global scale to generate a high-resolution digital topographic database of Earth (February of 2000). The SRTM water body dataset was produced from 1 arc-second digital terrain elevation data by the National Geospatial-Intelligence Agency (NGA). The National Topographic Data Base (NTDB) comprises of digital vector data sets that cover the entire Canadian landmass. The NTDB includes a layer for hydrographic features. Canada (North of 60 ° N) United States and Canada (South of 60°N) Alaska (North of 60°N) The National Land Cover Dataset is a Landsat based land cover database prepared by a consortium of agencies called Multi-Resolution Land Characteristics (MRLC) Consortium. The classification scheme includes a ‘water’ category which includes water bodies and generally has less than 25% cover of vegetation or soil. Methodology: The 1 arc-second pixels were coded with a value of 1 (water). All other regions were coded with a value of 0 (land).The ‘Block statistics’ tool from ArcTools was used to sum the number of 1 arc-second (~30-m) pixels within a non-overlapping 30 arc-second boundary. The resulting values were resampled to 30 arc-seconds and divided by 9 to get the percentage of water pixels within a 30 arc-second extent. 1 arc-second land- water mask 30 arc-second sub pixel analysis - Water - Land 83 75 92 87 95 64 99 59 100 83% 17% (750 pixels) 150 (pixels) Acknowledgements: This poster is based upon work supported by the National Aeronautics and Space Administration under Agreement No. NNH06AE47I issued through the Terrestrial Ecology Program, Earth Sciences Directorate. Sub-pixel Land-Water Mask Contact Information: *Latha Baskaran (baskaranl@ornl.gov)baskaranl@ornl.gov The sub-pixel product is available from the MAST-DC website - http://nacp.ornl.gov/mast-dc/