ECHO

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ECHO
Backtrack Algorithm and MISR Backtrack
Example Lei Fang January 23, 2007
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Agenda

• What is Backtrack?
• How do data providers configure orbit data?
• Example MISR Backtrack
• How does ECHO search for orbit data?

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What is Backtrack?

• An algorithm for searching orbit swath data
  (developed by Ross Swick from NSIDC, see
  http//geospatialmethods.org/bosa/ for more
  details)

A typical orbit path
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What is Backtrack?
Tough to represent spatial coverage in polar area
with conventional search solution
--Geodetic/Cartesian polygon
The same orbit path showing on map
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What is Backtrack?

• Backtrack solution If you are searching for
  orbital data, its probably a good idea to use
  orbits. Ross Swick

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What is Backtrack?

• Backtrack orbit model
• Three parameters to define an orbit
• Instrument swath width (in kilometers)
• Satellite declination or inclination (in degrees)
• Satellite period (in minutes)
• Orbit data representation
• Three parameters to represent orbit data
• Equatorial crossing longitude
• Start circular latitude (or start latitude and
  start direction)
• End circular latitude (or end latitude and end
  direction)

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How do data providers configure orbit data?

• Add orbit parameters to Collection Metadata (ECHO
  format)
• ltSpatialgt ltSpatialCoverageTypegtHorizontallt/Spatial
  CoverageTypegt ltOrbitParametersgt
• ltSwathWidthgt400lt/SwathWidthgt
• ltPeriodgt98.88lt/Periodgt
• ltInclinationAnglegt98.2lt/InclinationAnglegt
• lt/OrbitParametersgt
• ltGranuleSpatialRepresentationgt
• ltOrbit/gt
• lt/GranuleSpatialRepresentationgt
• lt/Spatialgt

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How do data providers configure orbit data?

• Add orbit data to Granule Metadata (ECHO format)
• ltSpatialgt
• ltSpatialDomainContainergt
• ltHorizontalSpatialDomainContainergt
• ltOrbitgt
• ltAscendingCrossinggt160.14462465545338lt/Ascend
  ingCrossinggt ltStartLatgt69.021242lt
  /StartLatgt
• ltStartDirectiongtDlt/StartDirectiongt
• ltEndLatgt-68.995831lt/EndLatgt
• ltEndDirectiongtAlt/EndDirectiongt
• lt/Orbitgt
• lt/HorizontalSpatialDomainContainergt
• lt/SpatialDomainContainergt
• lt/Spatialgt

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Example MISR Backtrack

• Multi-angle Imaging Spectro-Radiometer (MISR)
  data helps to understand Earth's climate.
• See http//terra.nasa.gov/About/MISR/about_misr.ht
  ml
• for more information
• Configuring MISR orbit data requires additional
  work
• Missing information in the metadata file such as
  orbit parameters
• Spatial data elements are at different places in
  metadata file
• Some information is stored in a separate file
• Solution
• Add missing information to metadata file
• Modify BMGT-to-ECHO XSLT ingest script

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Example MISR Backtrack

• Add missing orbit parameters to collection
  metadata
• ltSpatialgt ltSpatialCoverageTypegtHorizontallt/Spatial
  CoverageTypegt ltOrbitParametersgt
• ltSwathWidthgt400lt/SwathWidthgt
• ltPeriodgt98.88lt/Periodgt
• ltInclinationAnglegt98.2lt/InclinationAnglegt
• lt/OrbitParametersgt
• ltGranuleSpatialRepresentationgt
• ltOrbit/gt
• lt/GranuleSpatialRepresentationgt
• lt/Spatialgt

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Example MISR Backtrack

• Modify BMGT-to-ECHO XSLT ingest script to weave
  orbit data for granule metadata
• AscendingCrossing
• The data under EquatorCrossingLongitude element
  in BMGT metadata input file is a descending
  crossing
• ltOrbitCalculatedSpatialDomaingt
• ltOrbitCalculatedSpatialDomainContainergt
• ltOrbitNumbergt10429lt/OrbitNumbergt
• ltEquatorCrossingLongitudegt-32.205375344546
  6lt/EquatorCrossingLongitudegt
  ltEquatorCrossingDategt2001-12-03lt/EquatorCrossingDa
  tegt ltEquatorCrossingTimegt124219.8204850lt/Equator
  CrossingTimegt
• lt/OrbitCalculatedSpatialDomainContainergt
• lt/OrbitCalculatedSpatialDomaingt
• XSLT script
• Extracts descending crossing -32
• Adds placement -167 to adjust to ascending
  crossing -32-168
• Normalizes to (-180, 180) -32-168360 160
• Adds to spatial section to ECHO format output
  ltAscendingCrossinggt160lt/AscendingCrossinggt

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Example MISR Backtrack

• Latitude
• The data under PSA element in BMGT metadata input
  file as a block number, a separate block-latitude
  lookup table file is provided
• ltPSAsgt
• ltPSAgt
• ltPSANamegtSP_AM_MISR_EndBlocklt/PSANam
  egt
• ltPSAValuegt177lt/PSAValuegt
• lt/PSAgt
• ltPSAgt
• ltPSANamegtSP_AM_MISR_StartBlocklt/PSAN
  amegt
• ltPSAValuegt35lt/PSAValuegt
• lt/PSAgt
• lt/PSAsgt
• XSLT script
• Extracts value from SP_AM_MISR_StartBlock 35
• Looks up latitude from lookup table 69
• Determines the direction from path pattern in the
  lookup table descending
• Applies to end latitude latidue is -68 for block
  177, and it is ascending
• Adds to spatial section to ECHO format output

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How does ECHO search for orbit data?

• User specifies a regular spatial window
• ltgranuleConditiongt
• ltspatialgt
• ltPolygongt
• ltLRinggt
• ltCListgt-90,49,-90,39,-70,39,-70,49,-90
  ,49lt/CListgt
• lt/LRinggt
• lt/Polygongt
• ltSpatialTypegt
• ltlistgt ltvaluegtORBITlt/valuegt lt/listgt
• lt/SpatialTypegt
• lt/spatialgt
• lt/granuleConditiongt

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How does ECHO search for orbit data?

• Backtrack calculates from both ascending and
  descending path for equatorial longitude
  crossings and start/end circular latitudes
  according to users query window

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How does ECHO search for orbit data?
Search ascending path
End Circular Lat 49N
Start Circular Lat 39N
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How does ECHO search for orbit data?
Search descending path
Start Circular Lat 131
End Circular Lat 141
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How does ECHO search for orbit data?

• Sample SQL where condition
• ( ( ( (start_clat between 39.0 and 49.0) or
• (end_clat between 39.0 and 49.0) or
• (start_clat lt 39.0 and end_clat gt 49.0) ) and
• ( ascending_crossing between -80.0 and -64.0) )
  or
• ( (start_clat between 131.0 and 141.0) or
• (end_clat between 131.0 and 141.0) or
• (start_clat lt 131.0 and end_clat gt 141.0) ) and
• (ascending_crossing between 88.0 and 106.0) ) ) )