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The marine geoid and its importance to ocean current monitoring
Dagny I. Lysaker
Meeting in the Nordic Working group on geoiddetermination, Helsinki 10.-11. March 2010
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A more precise geoid model has improved height determination using GNSS over land
GNSS – levelling ≈ geoid = HREF > GNSS – HREF = height value
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Credits to CNES (www.cnes.fr)
A more precise marine geoid will imrpove the modelling of ocean currents
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MDT = MSSH - N
A more precise marine geoid will imrpove the modelling of ocean currents
Credits to CNES (www.cnes.fr)
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Oceanographers determine MDT from measurements of temperature and salinity and
by hydrodynamic modelling
Credits to: www.oceanographers.ru
Credits to: www.aviso.oceanobs.com
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Surface currents may be obtainedfrom the slope of the MDT
Ocean currents originate form pressure gradients in the oceanWhen the pressure gradient is balanced by the Coriolis effect
Geostrophic balance
u=−gf R
∂
∂, v=
gf R cos
∂
∂
f =2 sin
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OCTAS -Ocean Circulation and Transport between the North Atlantic and the Arctic Sea
Courtesy Kourosh Ghazavi
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The geodetic model show more detailsthan the oceanographic model
Oceanographic model Geodetic model
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The geodetic model show smallercurrents than the oceanographic model
Oceanographic model (OCCAM) Geodetic collocation model
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The collocation solution has morepronounced currents than direct subtraction
Geodetic collocation model (MSSH S(g))
Geodetic direct subtraction model (MSSHN)
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The geodetic model agrees with drifter data
Mean: 12,5 cm/s
Standard deviation: 9,9 cm/s
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Mean: 12,5 cm/s
Standard deviation: 9,9 cm/s
The geodetic model agrees with drifter data
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Drifter data have the same fit to mooring data as our models
Model Mean Stdsubtracted (cm/s) (cm/s)
8.6 5.3
SMDT 10.1 5.2OCCAM 7.3 4.4drifter 7.9 6.7
MDT_LSC
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Summary
Ocean currents may be determined from altimetry and gravity
MDT is an important climate parameter
MSSH at high latitude needs improvements
The marine geoid needs improvements
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KARTDATA TIL NYTTE FOR SAMFUNNET
Ocean currents may be determined from altimetry and gravity
MDT is an important climate parameter
MSSH at high latitude needs improvements
The marine geoid needs improvements
QUESTIONS?