the octas project, the geoid, the mean sea surface and and the mean dynamic topography by dag...
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The OCTAS Project, the geoid, the mean
sea surface and and the mean dynamic
topographyBy
Dag Solheim
Norwegian Mapping Authority
Co-authors
A. Hunegnaw, O. Omang, A. Soltanpour (NMA), B. R. Pettersen, D. I.
Lysaker (UMB), H. Drange, J. Johannessen, F. Siegismund (NERSC),
H. Nahavandchi, K. Ghazavi (NTNU), A. Gidskehaug (UoB), H. P.
Plag (UNR)
OCTAS, Ocean Circulation and
Transport between the North Atlantic
and the Arctic Sea
OCTAS partnersNMA, Norwegian Mapping Authority
UMB, University of Life Sciences (NLH, Ås)
NERSC, Nansen Environmental and Remote Sensing Center
NTNU, Norwegian University of Science and Technology
UoB, University of Bergen
(UoO, University of Oslo)
External partners:
DNSC, Danish National Space Center
OSU, Ohio State University
UNR, University of Nevada Reno
UEDIN, University of Edinburgh
OCTAS and related research
projects
Interdisciplinary project
Educational part
• 4 PhD students
• OCTAS Study Course
• Enhance the Norwegian capabilities in
earth observation by using modern satellite
techniques in an interdisciplinary way
The OCTAS geoid
• Collect and validate existing gravity data
• Airborne Gravity Survey
• Adjustment of marine gravity data
• Computation of the geoid using the best
available geopotential models
Gravity coverage
Marine Gravity Data
• Many old sources
– Errors due to navigation, pre GPS
– Blunders
– Data bias, insufficient tie to land gravity
– Data structure, often given as points and NOT
in a line/track-organized way
– Mixture of data from several surveys
Example, gravity blunder
Adjustment of data• Need data organized as tracks
• Each survey internally adjusted
• Compute bias for each survey
• However
– Data often given as points and not as tracks
– Some sources a mixture of data from several
surveys
• UEDIN, network adjustment
Difference between adjusted and non-
adjusted gravity data (mgal)
OCTAS v4 geoid (m)
Altimetry derived MSS
Challenges
• OCTAS primary study area, Fram Strait
between Greenland and Svalbard
• Limited number of satellites, ERS1/2,
Envisat
• Significant amount of sea ice
• Limited number of retracked data available
(outside the scope of OCTAS)
OCTAS v3, MSS (m)
OCTAS MDT, MSS-Geoid (m)
OCCAM MDT (m)
Optimal estimation of the geoid
and the MDT
• Least Square Collocation, LSC
– Covariance function modeling
• Iterative Combination Method, ICM
– Developed by R. Hipkin and A. Hunegnaw at
the University of Edinburgh
OCTAS, LSC MDT
OCTAS, ICM MDT, KMS04 & FOAM
Bathymetry
Post OCTAS Activity
• MSS in the Fram Strait, retracking
• Geoid computation
• Gravity compiling, error screening
• Marine survey in 2007 in cooperation with
the Norwegian Coast Guard and University
of Bergen
• GOCE