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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
  • Dr. Yan M Wang and Dr. Daniel R Roman
  • Geodesist, National Geodetic Survey
  • 301-713-3202 x 127
  • 301-713-3202 x 161