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GEOID03 in Louisiana and Alaska. Dr. Yan M Wang and Dr. Daniel R Roman Geodesist, NGS/NOAA ACSM Annual Conference and Technology Exhibition Orlando, FL April 21-26, 2006. Outline. GEOID03 update in Louisiana GEOID03 in Alaska. Geoid03 update in Louisiana.

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Geoid03 in louisiana and alaska

GEOID03 in Louisiana and Alaska

Dr. Yan M Wang and Dr. Daniel R Roman

Geodesist, NGS/NOAA

ACSM Annual Conference and Technology Exhibition

Orlando, FL

April 21-26, 2006


  • GEOID03 update in Louisiana

  • GEOID03 in Alaska

Geoid03 update in louisiana
Geoid03 update in Louisiana

  • Subsidence corrections to the leveling network (85 pts) provided by LSRC

  • Subsidence corrections are computed from a model, and further improvement is expected

  • The leveling network will be readjusted in the National Spatial Reference System in February, 2007.

Few remarks
Few Remarks

  • Updated Vertical Time-dependent Positioning bench marks must be used for all applications

  • New survey along one long level line of 40 km, running from the coast inland as close to North/South is under discussion

The geoid in alaska
The Geoid in Alaska

  • NGS has computed a gravimetric geoid for Alaska as a separate computational area since GEOID96

  • Gravimetric only; No hybrid possible

    • Lack of wide-spread GPS on leveled benchmarks

    • Refers to ITRF origin, not NAD 83

Simplified Concept of NAD 83 vs. ITRF

Earth’s Surface



hNAD83 – hITRF varies

smoothly by latitude

and longitude

ITRFxx origin

~2.24 m

NAD 83 origin

Gravity Holdings Zoom near Nome

- Note lack of good near-shore data

- Some sparseness in terrestrial network

- Airborne gravity could solve both of these

Geoid99 vs geoid03 in alaska
GEOID99 vs GEOID03 in Alaska

  • An error in how OPUS estimates orthometric heights was found during FAA airport surveys

    • OPUS/GPS yields NAD 83 ellispoid height

    • GEOID99 is an ITRF/GRS80 geoid height

    • Incompatible!

  • GEOID03 was created in Alaska to fix this problem

Alaskan GEOID99 vs GEOID03

Earth’s Surface


GEOID03 (refers to

NAD 83 centered


GEOID99 (refers to

ITRF96 centered





Note: Physical location

of geoid In space

has not changed

from 99 to 03!

ITRF96 origin


~2.24 m

Erroneously, OPUS was doing:


Now, correctly, OPUS does:


NAD 83 origin

The geoid in alaska 2
The Geoid in Alaska (2)

  • Ongoing research

    • GPS on leveled benchmarks vs GEOID03

    • Accuracy assessments

    • Better theory

    • Better data

  • Airborne gravity

    • Most logical way to collect accurate data in areas previously unvisited

Final snag heights change over time
Final snag: Heights change over time!

  • All heights needs monitoring:

    • Crustal motion (affects H, h)

    • Gravity changes (affects H, N)

    • h=H+N

  • Monitoring can be done efficiently:

    • GPS for crustal monitoring

    • Spot gravity re-visits for gravity monitoring

    • Re-leveling is not efficient

  • Lest we forget, Alaska has some very active geology…

Questions comments