Transcript PowerPoint プレゼンテーション

Wetlands mapping 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
What is a wetland?
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)
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)
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 methane gas
Wetlands are one of the most important ecosystems in the world.
It is important to inventory and monitor wetlands.
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.
Objective
To extract wetlands in North America
using MODIS 2008 data
Advantages of MODIS data:
• With high frequency repeat coverage
• Significant potential for mapping large wetland extent and dynamics
• Lower cost
Study area
North America is defined in this study as Canada, United States , Mexico, the countries
of Central America and the Caribbean Islands.
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):
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)
Definition
－ Land cover legend
Code
Class name
R,G,B (color code)
1
Broadleaf evergreen forest
0,50,0
2
Broadleaf deciduous forest
60,150,0
3
Needleleaf evergreen forest
0,110,0
4
Needleleaf deciduous forest
85,110,25
5
Mixed forest
0,200,0
6
Tree open
140,190,140
7
Shrub
190,190,0
8
Herbaceous
255,255,50
9
Herbaceous with sparse tree / shrub
180,230,100
10
Sparse vegetation
255,255,205
11
Cropland
255,175,80
12
Paddy field
145,50,230
13
Cropland / other vegetation mosaic
220,160,255
14
Mangrove
155,130,230
15
Wetland
180,250,240
16
Bare Area,consolidated(gravel,rock)
150,150,150
17
Bare Area,unconsolidated (sand)
200,200,200
18
Urban
255,0,0
19
Snow / ice
250,250,250
20
Water bodies
175,210,240
20 land cover classes are defined by Land Cover Classification System (LCCS)
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
Methodology
－The flow of the study
23 period of
Reference
data
Training data
MCD43A4(2008)
Preprocessing
III
II
NDWI
I
NDSI
STRM 90m
GLCNMO
Decision tree model
Non-vegetated area
IV
Vegetated area
MODIS Tasseled Cap Indices
Maximum likelihood classification
Wetland map
Validation
II
V
Methodology
－Part I: MODIS preprocessing
Download the MCD43A4
Mosaic the tiles
Resampling
Modis
Reprojection
Tool
(MRT)
Reprojection
Cloud removal
Cloud free data
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.
Methodology
－Part II: NDWI & NDSI
Normalized Difference Water Index (NDWI):
 NIR1   NIR 2
NDW I 
 NIR1   NIR 2
(Gao, 1996)
Normalized Difference Snow Index (NDSI):
 Green   NIR1
NDSI 
 Green   NIR1
(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 for
using moderate resolution imaging spectroradiometer data Remote Sensing of Environment, 1995
mapping global snow cover
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)
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).
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,
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
Yes
Wetland&Other vagetation
Snow
No
Water
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”.
Result
Wetlands
Others
Water
Comparison (1)
－Everglades National Park (United States)
Result of this study
GLOBCOVER
Google Earth image
GLC2000
Comparison (2)
－Reserva de la Biosfera Ría Celestún (Mexico)
Result of this study
GLOBCOVER
Google Earth image
GLC2000
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.
Thank you for your attention!
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
Background
－Global wetland databases
Name:Global wetland distribution
Name:Distribution of wetlands
Name:Global lakes and wetlands database
Resolution:
Resolution:
Resolution:1km
Year:1987
Year:
Year:2004
Wetlands
Wetlands
Name: GLC2000
Resolution: 1km
Year:2000
Wetlands
Name: GLCNMO
Name: GLOBCOVER
Resolution: 1km
Resolution: 300m
Year:2003
Year:2005