GEOID03 in Louisiana and Alaska

1
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

2
Outline

• GEOID03 update in Louisiana
• GEOID03 in Alaska

3
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.

4
(No Transcript)
5
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

6
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

7
Simplified Concept of NAD 83 vs. ITRF
Earths Surface
hNAD83
hITRF
hNAD83 hITRF varies smoothly by latitude and
longitude
ITRFxx origin
2.24 m
NAD 83 origin
8
(No Transcript)
9
Gravity Holdings Zoom near Nome - Note lack of
good near-shore data - Some sparseness in
terrestrial network - Airborne gravity could
solve both of these
10
(No Transcript)
11
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

12
Alaskan GEOID99 vs GEOID03
Earths 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 Hh83-N99 Now,
correctly, OPUS does Hh83-N03
NAD 83 origin
13
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

14
Final snag Heights change over time!

• All heights needs monitoring
• Crustal motion (affects H, h)
• Gravity changes (affects H, N)
• hHN
• 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

15
Questions/Comments?

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