Geoscience Reference
In-Depth Information
one-sided perspective, but it was used against scientists who claimed,
still around 1960, that the gravimetric method was able to do every-
thing that satellite geodesy could. With GPS now we know better, and
without ideological scruples we combine satellite data with terrestrial
gravity.
(A second perspective of astronomical observations is the astrogeode-
tic geoid determination. Here the accuracy of astronomy is sucient;
cf. Sec. 5.14.)
Final remark
The computation of Molodensky reductions is heavy work. So in mountain-
ous areas, least-squares collocation is definitely preferable to integration,
except for certain test computations (Sideris 1987, 1990).
Collocation also permits comparison and combination of astrogeodetic
and gravimetric data; a key paper is Kuhtreiber (2002 b).
All this, however, builds on the fundamental ideas of M.S. Molodensky.
In his landmark publication (Krarup 1969) one clearly sees the transition
from Molodensky's problem to least-squares collocation.
11.4
The geoid on the internet
The International Association of Geodesy (IAG) has a very active Interna-
tional Geoid Service (IGeS-IAG). Before you try to compute your own geoid,
look at www.iges.polimi.it to see what is available there. You can find global
and regional geoids, data, software, references, plans for future work, etc.
We particularly mention the geoid repositories:
•
www.iges.polimi.it/index/geoid repo/global models.htm ,
•
www.iges.polimi.it/index/geoid repo/regional models.htm .
In the latter file you can find:
•
USA gravimetric Geoid 1996 (Dru Smith),
•
European Geoid/Quasigeoid EGG97 (H. Denker),
•
Austrian Geoid 1996 (H. Sunkel).
Other important internet addresses:
•
International Gravity Bureau (Toulouse):
http://bgi.cnes.fr8110/bgi a.html ,
•
International Association of Geodesy:
www.iag aig.org .
