vii berichte von fachinstituten an universitäten und technischen

390 Fachinstitute an Universitäten und Hochschulen
Figure 12: Amazon and Ganges catchments show significant variations within the time series generated using different filters
Survey of vertical gravity gradients in Baden-Württemberg
and Bavaria for GOCE-GRAND II project
For the GOCE GRAND II validation project the Bundesamt
für Kartographie und Geodäsie (BKG) measured new
gravity data sets of existing gravity points all over Germany.
For 14 of these observation points in Baden-Württemberg
and Bavaria the Institute of Geodesy supported the BKG
in the gradient measurements. The points were surveyed
with the absolute gravimeter Micro-g A10 of the BKG. The
sensor height of the A10 is approximately 70cm. To bring
down the absolute gravity value to the benchmark information
about the accurate local gravity gradient is required.
This is one field in the range of applications of a gravimeter
like the Scintrex CG-5.
All measurements were accomplished within 3 long survey
days. Planning the measurements was done on basis of the
official drafts of the survey offices, new snapshots made
Figure 13: Tripod of BKG with
CG-5 in the upper level
Figure 14: Measurement at Buchenberg
during the preceding absolute measurements and standard
mapping-and-routing services available on the web.
Compared to the drafts the up to date photos were the best
help on site to find the benchmarks easily. It took 2 sometimes
3 hours to reach each of the widespread points in the
field. This was mostly dependent on traffic situation and
transport connection/accessibility between the points.
Measuring a single gradient took around 45 minutes.
The gradient was surveyed with a special tripod, made by
the BKG. Each of the 2 levels of the tripod can be leveled
independently. So it was possible to ‘jump’ between the 2
levels to take 3 observations per level fast and precise. One
observation was averaged out of 3 readings which took 45
seconds. These data were analyzed, drift corrected and
checked for outliers (Grubbs algorithm). A plot (Figure 15)
of the measurement data verified the numerical output of
the gravity gradient and its accuracy.