Abstract: For nearly 20 years Very Long Baseline Interferometry
(VLBI) has been a premier geodetic technique. In the
early ’70s VLBI was used to measure transcontinental
baselines to an accuracy of a few decimeters. By the late
’70s length accuracies under 2 cm were routine. In the
’80s VLBI grew into a mature science. VLBI measure-
ments of absolute station position and long baselines are
the most accurate of any competing technique. Over 125
station positions were measured using VLBI. The accu-
racy of the best VLBI experiments is 5 parts in 10” -- 5
mm on 10,000 km baselines. VLBI routinely achieves ac-
curacy of a few millimeters on a few hundred kilometer
baselines. This great accuracy resulted in the direct con-
firmation of continental drift, which had previously only
been inferred from geologic data averaged over tens of
thousands to millions of years. The uncertainty in the
rate determinations is typically less than 1 mm/year.
In the early and mid-go’s a series of regional VLBI cam-
paigns were conducted in Alaska and southern California
to measure crustal deformation. Although scientifically a
success, these campaigns were discontinued for budget-
ary reasons. Recently many of these sites have been re-
visited by GPS receivers as part of NASA’s Dynamics of
the Solid Earth Program (DOSE). The consistency of the
GPS and VLBI measured station position is a critical sci-
entific question. If the station positions measured by the
two techniques are consistent, it is possible to combine
measurements made at different epochs with different
techniques to obtain information about station velocities.
By examining a campaign in southern Alaska, we verify
that the GPS and VLBI measured station positions are
consistent at the 15 mm level.
The International GPS Service for Geodynamics (IGS)
co-ordinates the placement of GPS receivers and data ar-
chiving on an international level. Presently there are 54
receivers in this network. Of these, more than 20 are co-
located with VLBI sites, past or present. A comparison of
the station coordinates of this global network found by
the two techniques gives good agreement. The RMS dif-
ference between the east and north coordinates is roughly
10 mm. The RMS difference between the local up coordi-
nate is three times larger, at roughly 30 mm.
Publication Year: 1994
Publication Date: 1994-09-23
Language: en
Type: article
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