A Comparison of Continuation Models for Optimal

Transformation of Gravimetric Data

By: Joanelle BaptisteElizabeth City State University, NC

Supervisor: Dr. Daniel Roman8/6/04

Line Office (Overview)

NOAA Ocean Service (NOS)

National Geodetic Survey (NGS)

Geosciences Research Division (GRD)

Terms to be familiar with

• Ellipsoid• Geoid• Gravimetric• Gravity anomaly: Δg = gobs-γ• Mean Sea Level

Models of the Earth

Figure of the Earth

OCEAN

Earth’s

Surface

“Ellipsoid”

Geopotential Surface

Geopotential Surface

Geopotential Surface

“Geoid”

P

Q

h

N

Geoid height N = h – HGravity anomaly Δg = gP0 – γQ

P0

plumb lineEllipsoid height, h = distance along ellipsoid normal (Q to P)

Orthometric height, H = distance along plumb line (P0 to P)

Geoid height, N = distance along ellipsoid normal (Q to P0)

P, Q and P0 all have the same lat, lon values.

H

∟

∟

Planar Approach

Earth’s curved surface

flat plane of the model space

Findings: predicted less actual

Height1km

Min.-0.8

Max.0.9

Ave.0.0

St. Dev.0.1

2km -1.7 1.6 -0.2 0.23km -2.8 2.2 -0.5 0.24km -3.9 2.5 -0.9 0.35km -5.2 2.4 -1.5 0.46km -6.3 2.3 -2.3 0.47km -7.7 1.8 -3.2 0.58km -9.1 1.1 -4.2 0.59km -10.6 0.4 -5.4 0.6

10km -12.2 -0.8 -6.7 0.6

Standard Deviation

0.00.20.40.60.8

1 2 3 4 5 6 7 8 9 10

Elevation(km)

Cha

nge

in

Nor

mal

Gra

vity

(m

gals

)

Series1

Minimum(blue), Maximum(lavendar), and Average (yellow) Differences

-15.0-10.0

-5.00.05.0

Elevation (km)

Cha

nge

in

Nor

mal

G

ravi

ty

(mga

ls)

Minimum ValueMaximum ValueAverage Value

Residual Values 1 km 8 km

Conclusion

• The planar method can be used to upward (or downward) continue data with some controls

• Because of systematic effects (ringing), a region for continuation larger than actually desired should be used (add about 0.5 degrees to latitude/longitude limits)

• Systematic average must also be accounted for and may be data dependent (i.e., a bias is introduced)

Importance of this Research

• Supervisor/field assignment• Operational applications

- Engineering- Navigational aid- Storm surge

- Coastal flooding

Accomplishments via EPP

Contributions:

Participant

NOAA

Acknowledgements• NOAA EPP staff• Dr. Daniel Roman• Mr. Edward Allen• Mr. Eric Linzey• Ms. Sonita Tiwari• Ms. Lucy Hall• Ms. Laura Cutrer • Class of 2004 (all my love)

Questions?

The End