MODIS Land ISIN Grid

1
MODIS Land ISIN Grid

• MODIS Land Validation Workshop
• January 22, 2001
• Robert WolfeNASA GSFC Code 922, Raytheon
  ITSSMODIS Land Science Team Support Group

2
Land Product Characteristics

• HDF-EOS Format
• Average size is about 70 MB

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MODLAND Grids

• Fine resolution grids for the L2G, 3 and 4
  products are based on two map projections
• Integerized Sinusoidal Grid (ISIN)
• Lambert Azimuthal Equal-Area (LAEA) (polar grids)
  
• Almost all of the fine resolution products will
  be made in the ISIN
• Exception Sea-ice products are made in the in
  the LAEA projection with the grid centered at
  the north and south poles (EASI Grid
  implementation)
• Grid cell size varies by product and is either
  (approx.) 0.25 km, 0.5 km or 1 km actual size
  depends on the projection
• Each grid is broken into non-overlapping tiles
  which cover approx. 10 x 10 deg. area
• Coarse resolution global Climate Modeling Grid
  (CMG) products are made in a geographic
  projection with grid cell sizes of 0.25 or 0.5
  deg.

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ISIN Grid
Grid Cell Sizes 30 arcsec (0.93 km) 15
arcsec (0.46 km) 7.5 arcsec (0.23 km)
10 degree Tiles
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History

• Selected 5 years ago for overall MODIS grid
• Compromise between land, ocean and atmosphere
  requirements
• First recommended for use for data analysis by
  Rossow Garder (1984)
• Used in the past by WMO, International Satellite
  Cloud Climatology Project (ISCCP), Oceans
  Pathfinder and SeaWiFS project, SSM/I and POLDER

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Example 5 Degree Grid
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Normal vs. Integerized Grid
Full Cell
Partial Cell

• Normal grid has partially filled cells along
  edges of grid

Integerized Grid
Normal Grid
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Brick-like Shifts
Before Projection
Before Projection

• Brick-like shifts between rows

After Projection
After Projection
250 m
Normal Grid
Integerized Grid
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Advantages/Disadvantages

• Advantages
• Global
• Non-interrupted
• Almost equal area (not quite near poles)
• Can be aligned at any meridian by sliding rows
• Continuous across end of rows
• Disadvantages
• Not supported by most tools
• Distorts shape of land areas
• Difficult to nest multiple resolutions
• Brick-like layout makes many geometric operations
  difficult non-horizontal gradients, resampling,
  frequency filtering, etc.
• No heritage in Land community

10
Tools

• Reprojection tool developed by USGS EDC and South
  Dakota School of Mines
• Converts MODIS L3 products to other grids (also
  converts format)
• Currently beta testing by MODIS Science Team
• Release expected on Feb. 28
• General Cartographic Transformation Package
  (GCTP)
• Updated by ECS to support ISIN and part of SDP
  toolkit
• USGS/EDC adding ISIN to official version
• Used by many vendors precursor for support
• Other vendor support
• Seems to coming along, but not as quickly as we
  would like