Transcript Sub-pixel Analysis of a 1-km Resolution Land-Water Mask North American Carbon Program

Sub-pixel Analysis of a 1-km Resolution Land-Water Mask
*Latha Baskaran, Bob Cook and Suresh Kumar Santhana-Vannan
Environmental Sciences Division
Oak Ridge National Laboratory
Oak Ridge, TN 37830
North American
Carbon Program
Alaska (North of 60°N)
Introduction:
Sub-pixel Land-Water Mask
• 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 arcseconds 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.
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.
Canada (North of 60°N)
United States and Canada (South of 60°N)
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).
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
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.
30 arc-second sub
pixel analysis
17%
150
(pixels)
99 100
83 100
95 100
83%
(750 pixels)
92 100
87 100
75 100
64 100 100
- Land
- Water
59 100
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.
Contact Information:
*Latha Baskaran ([email protected])
The sub-pixel product is available from the MAST-DC website - http://nacp.ornl.gov/mast-dc/
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%