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Wetlands mapping in North America using MODIS 500m imagery

Wetlands mapping in North America using MODIS 500m imagery. July 28, 2011. ○ Gegen Tana a , Ryutaro Tateishi b. a Graduate Schools of Science, Chiba University b Center for Environmental Remote Sensing (CEReS), Chiba University. What is a wetland?. Background.

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Wetlands mapping in North America using MODIS 500m imagery

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  1. Wetlandsmapping in North America using MODIS 500m imagery July 28, 2011 ○Gegen Tanaa, Ryutaro Tateishib a Graduate Schools of Science, Chiba University b Center for Environmental Remote Sensing (CEReS), Chiba University

  2. What is a wetland?

  3. Background －Definition of wetlands (Broadly used) The Ramsar convention (Ramsar 2004) defined wetlands as areas of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six meters. Ramsar Convention: The Convention on Wetlands, signed in Ramsar, Iran, in 1971, is an intergovernmental treaty which provides the framework for national action and international cooperation for the conservation and wise use of wetlands and their resources. (source – the Convention on Wetlands website)

  4. Background －Global wetlands locations in the Ramar Convention 160 countries participate in and 1953 wetlands are contained. Total surface area of designated sites (hectares): 190,455,433 The Ramsar definition of "wetlands" is a broad one, including not just marshes, fen and peatland, but also lakes, coral reefs, temporary pools, even underground caves, and all sorts of other systems everywhere from the mountains to the sea, including man-made habitats. (source – the Convention on Wetlands website)

  5. Background －The values of wetlands • The provision of water • A supplement of groundwater • Regulation of water quantity & flood control • Wildlife habitat • Retention of nutrients and carbon • A source of methanegas Wetlands are one of the most important ecosystems in the world. It is important to inventory and monitor wetlands.

  6. Background －Global wetland databases Global wetland databases: • Global wetland distribution (http://data.giss.nasa.gov/landuse/wetland.html) • Global distribution of wetlands map (http://soils.usda.gov/use/worldsoils/mapindex/wetlands.html ) • Global lakes and wetlands database (http://gcmd.nasa.gov/) Global land cover maps which include wetlands: • GLC2000 • GLCNMO • GLOBCOVER Problems existed in the wetlands maps on large scale: • Underestimate wetlands areas due to the spectral heterogeneity of wetlands. • Difficult to separate wetlands from other vegetation types such as forest, herbaceous and shrub.

  7. Advantages of MODIS data: • With high frequency repeat coverage • Significant potential for mapping large wetland extent and dynamics • Lower cost Objective • To extract wetlands in North America using MODIS 2008 data

  8. Study area North America is defined in this study as Canada, United States , Mexico, the countries of Central America and the Caribbean Islands.

  9. Data used －Nadir BRDF-Adjusted Reflectance MCD43A4:Terra+Aqua Nadir BRDF-Adjusted Reflectance 16-Day L3 Global 500m SIN Grid V005 (All 23 periods of 2008) Spectral bands (1-7):

  10. Data used －Digital elevation model and reference data Digital elevation model: • SRTM DEM, 90m (version 4.1) Reference data: • Landsat ETM+, 30m (Around 2008) • Google Earth images • Ramsar Convention sites • Existing land cover maps (GLCNMO, GLC2000, GLOBCOVER)

  11. Definition － Land cover legend 20 land cover classes are defined by Land Cover Classification System (LCCS)

  12. Definition －Definition of wetlands in LCCS LCCS definition: Land cover definition by Land Cover Classification System version 2 (LCCS2) developed by FAO( http://www.glcn-lccs.org/). Wetland formula in LCCS2: Closed to Open Woody Vegetation Water Quality: Fresh Water // Closed to Open Woody Vegetation Water Quality: Brackish Water // Closed to Open Herbaceous Vegetation. The main layer consists of closed to open woody vegetation. The crown cover is between 100 and 15%. The height is in the range of 7 - 2m. The main layer consists of closed to open herbaceous vegetation. The crown cover is between 100 and 15%. The height is in the range of 3 - 0.03m. Water Quality: Fresh Water or Brackish Water. Depending on the level of Total Dissolved Solids (TDS) expressed in parts per million (ppm), three classes are distinguished: fresh, brackish and saline water (Cowardin et al., 1979). 1) Fresh Water: Less than 1 000 ppm TDS. 2) Brackish Water: Between 1 000 and 10 000 ppm TDS. 3) Saline Water: More than 10 000 ppm TDS Three main components: Hydrology, Soil and Vegetation

  13. Methodology III I II IV II V －The flow of the study 23 period of MCD43A4(2008) Reference data Training data Preprocessing NDWI NDSI STRM 90m GLCNMO Decision tree model Non-vegetated area Vegetated area MODIS Tasseled Cap Indices Maximum likelihood classification Wetland map Validation

  14. Methodology －Part I: MODIS preprocessing Download the MCD43A4 Mosaic the tiles Modis Reprojection Tool (MRT) Resampling Reprojection Cloud removal Cloud free data

  15. Methodology －Part II: MODIS Tasseled Cap Indices MODIS Tasseled Cap Indices:The tasseled cap transformation was first developed in 1976 for Landsat MSS data. It is one of the available methods for enhancing spectral information of Landsat TM. The tasseled cap transformation was extended to MODIS data (Zhang et al.(2002).Three of the six tasseled cap transform bands are often used. • Brightness: Measure of vegetation and soil • Greenness: Measure of vegetation • Wetness: Interrelationship of soil and canopy moisture MODIS TC coefficients (Lobster et al.(2007)): ZHANG, X.Y., SCHAAF, C.B., FRIEDL, M.A., STRAHLER, A.H., GAO, F. and HODGES, J.F.C.,2002, MODIS tasseled cap transformation and its utility. In Proceedings of the International Geoscience and Remote Sensing Symposium (IGARSS ’02), edited by, Toronto, Canada, 24–28 June (Piscataway, NJ: IEEE), pp. 1063–1065. LOBSER, S.E., COHEN, W.B., 2007, MODIS tasselled cap: land cover characteristics expressed through transformed MODIS data. International Journal of remote Sensing, 28, pp. 5079–5101.

  16. Methodology －Part II: NDWI & NDSI Normalized Difference Water Index (NDWI): (Gao, 1996) Normalized Difference Snow Index (NDSI): (D.K Halla, 1996) Bo-Cai G.NDWI--A normalized difference water index for remote sensing of vegetation liquid water from space, Remote sensing of environment, 1996, pp257-266 Dorothy K. Halla, George A. Riggsb and Vincent V. Salomonsonc. NDSI:Development of methods formapping global snow cover using moderate resolution imaging spectroradiometer data Remote Sensing of Environment, 1995

  17. Methodology －Part III: Dominant wetland types in North America O — Permanent freshwater lakes (over 8 ha) H — Intertidal marshes; includes salt marshes, salt meadows, saltings, raised salt marshes; includes tidal brackish and freshwater marshes. Tp - Permanent freshwater marshes/pools; ponds (below 8 ha), marshes and swamps on inorganic soils; with emergent vegetation water-logged for at least most of the growing season. F — Estuarine waters; permanent water of estuaries and estuarine systems of deltas. J — Coastal brackish/saline lagoons; brackish to saline lagoons with at least one relatively narrow connection to the sea. A — Permanent shallow marine waters in most cases less than six metres deep at low tide; includes sea bays and straits. E — Sand, shingle or pebble shores; includes sand bars, spits and sandy islets; includes dune systems and humid dune slacks. I — Intertidal forested wetlands; includes mangrove swamps, nipah swamps and tidal freshwater swamp forests. G — Intertidal mud, sand or salt flats. Xf - Freshwater, tree-dominated wetlands; includes freshwater swamp forests, seasonally flooded forests, wooded swamps on inorganic soils. (source – the Convention on Wetlands website)

  18. Methodology －Part III: Types of wetlands and Landsat ETM+ According to the vegetation types described in the LCCS, wetlands in North America were classified into three types. • Forest/Shrub dominant wetland (Inland) • Herbaceous dominant wetland (Inland) • Sea grass dominant wetland (Coastal) Totally 31 scenes of Landsat ETM+ images were used for collecting training sites. Principles of training data collection: 1. Training data should satisfy the LCCS definition. 2. MCD43A4 is MODIS data with the spatial resolution of 500m.The pure training site area should be selected larger than 250ha (3×3 pixels).

  19. Methodology －Part III: Training data collection Common part of existing maps Ramsar Convention Landsat ETM+ Google Earth Google Earth Non-vegetated*1 and vegetated *2 land cover types Wetland Collection of training data *1: Water, Snow, Urban, Bare (Rock&Sand) *2: Broadleaf evergreen forest, Broadleaf deciduous forest, Needleleaf evergreen forest, Needleleaf deciduous forest, Mixed forest, Tree open, Shrub, Herbaceous, Herbaceous with sparse tree/shrub, Sparse vegetation, Cropland, Paddy field, Cropland/other vegetation mosaic, Mangrove,

  20. Methodology －Part IV: Decision tree model STRM 90m <1000m Resampling Mask of Urban&Bare area (GLCNMO) NDSI_P10<0.1391 No Yes NDWI_8<0.2013 Snow Yes No Wetland&Other vagetation Water

  21. Methodology －Part V: Maximum likelihood method • Input satellite data: MODIS Tasseled Cap Indices (Brightness, Greenness, Wetness) • Period of data: Totally 12 periods, 36 scenes. (1,4, 8,11-18, 20,22) • Training data: Wetland (3 types) and other vegetated land cover types (According to the monthly changed Tasseled Cap _Greenness pattern, each land cover type was subclassified. ) • Integration: After classification, vegetated land cover types were integrated as “Others”, three types of wetlands were integrated as “wetland”.

  22. Wetlands Others Water Result

  23. Comparison (1) －Everglades National Park (United States) Result of this study GLOBCOVER Google Earth image GLC2000

  24. Comparison (2) －Reserva de la Biosfera Ría Celestún (Mexico) Result of this study GLOBCOVER Google Earth image GLC2000

  25. Conclusions and future works • In this study, wetlands defined in the LCCS were classified into three types and wetlands in North America with large spatial extent were successfully extracted. • MODIS tasseled Cap Indices (brightness, greenness and wetness), SRTM 90m, • NDWI and NDSI were confirmed useful for extracting wetlands. • Subclasses of land cover types especially for wetlands were very effective for • classification in this study. • However, because of the spectral heterogeneity of wetlands, some small extent of wetlands and narrow wetlands were failed to be extracted in this study. • Other reference data like Landsat ETM+ should be considered for mapping • small and narrow wetlands. • Quantitative validation should be also performed by using ground truth data. • (National Wetland Inventory: http://www.fws.gov/wetlands/) • Develop a wetland map of 2008 for global scale.

  26. Thank you for your attention!

  27. Background －Characteristics of remote sensing data for mapping wetlands High spatial resolution remote sensing data: Advantages: • Benefit on mapping wetlands in local and regional scales • With high accuracy in mapping small extent of wetlands Disadvantages: • Difficult to get global or continent range of wetlands map • Time consuming for mapping large wetlands • Higher cost (SAR data) Moderate spatial resolution remote sensing data: Advantages: • With high frequency repeat coverage • Significant potential for mapping large wetland extent and dynamics • Lower cost Disadvantages: • Unavoidably underestimate wetland area due to the small and fragmented nature • of many wetlands • Lower map accuracy

  28. Background Wetlands Wetlands Wetlands －Global wetland databases Name:Global wetland distribution Resolution: Year:1987 Name:Distribution of wetlands Resolution: Year: Name:Global lakes and wetlands database Resolution:1km Year:2004 Name: GLC2000 Resolution: 1km Year:2000 Name: GLCNMO Resolution: 1km Year:2003 Name: GLOBCOVER Resolution: 300m Year:2005

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