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