Merging Land

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Merging Land Ocean DataDavid T.
SandwellScripps Inst. Of Oceanography

• Why are the ocean basins so poorly charted?
• What can we do about it?
• What is the zero level for depth and height?
• Merging land and ocean data

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Earth vs. Mars
Mars Earths oceans today
horizontal resolution 2 km 25 km
vertical accuracy 1 m 250 m
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Depth Soundings - South Pacific
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Interstate Highways
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Why don't we map the oceans using ships?

• Typical ship track distribution is adequate to
  recover long-l depths (l gt 160 km) but usually
  inadequate for short-l recovery.
• Multibeam coverage is very sparse. It would take
  125 ship-years to map the deep oceans.

Maps are at scale scale (1-deg. grid). Spreading
ridge axis (right) has better-than-normal
coverage.
Section ?.?.?
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What can we do about it?

• Declassify US Navy bathymetry data.
• Improve public archives of multibeam bathymetry.
• Launch a new satellite altimeter.
• Map the oceans with multibeam echosounders.

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MEDEA Scientific Utility of Naval Environmental
Data, (Mitre, Co., June, 1995)
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MEDEA Scientific Utility of Naval Environmental
Data, (Mitre, Co., June, 1995)
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modern mapping tools
multibeam echo sounder
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NGDC Multibeam Bathymetry Holdings
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satellite altimetry
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available altimeter data

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gridded map products ? flow chart
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gravity anomaly

• use Laplace equation to convert slopes to gravity
  anomaly.
• restore long-? gravity model.

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bathymetry

• assemble available ship soundings and construct a
  long-? (? gt 160 km) depth model. (NGDC SIO
  maintain non-proprietary ship soundings.)
• remove ? gt 160 km from gravity grid.
• downward continue gravity to mean ocean depth.
• calibrate the topography-to-gravity ratio along
  ship tracks.
• multiply residual gravity by calibration factor.
• restore long-? depth grid.

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fundamental limitations

• downward continuation
• ocean waves
• coastal tides

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Scripps Workshop Report
Available at http//topex.ucsd.edu. Need both
satellites and ships to explore the ocean basins.
Report addresses science and applications from a
new altimeter mission.
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Merging land and ocean dataWhat is elevation?
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EGM96 Geoid Height
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Land Topography

• Shuttle Radar Topography Mission (SRTM)
• SRTM measures geometric height - sort of
• USGS distribution is geometric height - EGM96
• EGM96 does not capture scales lt 200 km

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conclusions

• improvements in marine bathymetry
• retracking altimeter waveforms - now
• need to improve access to multibeam data - now
• should continue MEDEA discussions on
  declassification of bathymetry - now
• need new altimeter mission - 6 years
• merging land and ocean data is problematic
• orthometric height geometric height - geoid
  height
• shorelines have gradual topographic gradient
  tides
• coastal bathymetry is generally poor

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extra slides
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MEDEA Scientific Utility of Naval Environmental
Data, (Mitre, Co., June, 1995)

• The Odyssey
• When Jason arrived in Colchis, Medea was old
  enough to marry. Jason told Aeetes of his quest
  for the golden fleece. Aeetes consented to give
  Jason the fleece if Jason would yoke two
  fire-breathing bulls to a plow and sow a field
  with the teeth of a dragon, from which it was
  well-known that a crop of armed men would spring
  up and turn their weapons against their producer.
  Jason talked to Medea. He promised to marry her
  if she would give him success. They stood before
  the altar of Hecate and called the goddess to
  witness his oath. Then Jason accepted Aeetes
  offer. Medea gave Jason a magic charm by which he
  could safely encounter the breath of
  fire-breathing bulls and the weapons of the armed
  men. Her spells caused the dragon that guarded
  the fleece to sleep.

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Trackline Hypsometry
Trackline-km / 10 m Depth Increment
Cumulative Trackline-km
1.00E00
1.00E01
1.00E02
1.00E03
1.00E04
1.00E05
1.00E06
1.00E07
1.00E08
1.00E09
0
2,000
4,000
Frequency
Cumulative
6,000
Depth
8,000
10,000
12,000
Total effort _at_ 8 kts 918 Ship-years minimum
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20
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40
50
60
80
100
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80 of effort will be expended in the top 200 m
of seafloor 20 of effort will go to the deep
ocean (gt 200 m depth)