Geoid03 in louisiana and alaska
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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

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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


Outline

Outline

  • 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


Geoid03 in louisiana and alaska

Simplified Concept of NAD 83 vs. ITRF

Earth’s Surface

hNAD83

hITRF

hNAD83 – hITRF varies

smoothly by latitude

and longitude

ITRFxx origin

~2.24 m

NAD 83 origin


Geoid03 in louisiana and alaska

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


Geoid03 in louisiana and alaska

Alaskan GEOID99 vs GEOID03

Earth’s Surface

hNAD83

GEOID03 (refers to

NAD 83 centered

ellipsoid)

GEOID99 (refers to

ITRF96 centered

ellipsoid)

hITRF00

N03

N99

Note: Physical location

of geoid In space

has not changed

from 99 to 03!

ITRF96 origin

Geoid

~2.24 m

Erroneously, OPUS was doing:

H≈h83-N99

Now, correctly, OPUS does:

H≈h83-N03

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

Questions/Comments?

  • Dr. Yan M Wang and Dr. Daniel R Roman

  • Geodesist, National Geodetic Survey

  • [email protected]

  • 301-713-3202 x 127

  • [email protected]

  • 301-713-3202 x 161


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