Jökull - 01.12.1973, Page 72

Gravity Base Station Network in Iceland 1968-1970
GUDMUNDUR PÁLMASON
NATIONAL ENERGY AUTHORITY, REYKJAVÍK, ICELAND
TOR H. NILSEN*
U. S. GEOLOGICAL SURVEY, MENLO PARK, CALIFORNIA 94025
GUNNAR THORBERGSSON
NATIONAL ENERGY AUTHORITY, REYKJAVÍK, ICELAND
INTRODUCTION
A network of 39 new gravity base stations was
established in Iceland during May, June and
September 1968. These stations were used as
bases for a regional gravity survey of Iceland
which was started in 1968. The base stations
are distributed almost equidistantly throughout
Iceland (Fig. 1), and are connected with the
base stations in Reykjavík. Although several
base stations in Reykjavík have been used in
the past (Fig. 2), Reykjavík A has hitherto
been the main base. However, because its loca-
tion is now impractical for general use, it has
been replaced by Reykjavík AA, which is locat-
ed in the building of the Science Institute of
the University of Iceland. Including the Reykja-
vík stations, a total of 46 gravity base stations
were occupied during the survey. Three La-
Coste and Romberg, Inc., Model G gravity
meters were used during the survey (Nos. 137,
140, and 144). Meters 137 and 144 were used
concurrently at all stations in the May—June
1968 survey, while meters 140 and 144 were
used in September 1968. Only meter 137 was
used in the Sept—Dec. 1970 survey, which was
carried out to improve earlier partly erroneous
observations at the Hveravellir base station.
Calibration tables for these meters were sup-
plied by Army Topographic Command (TOPO-
COM) (Table 1).
*) Formerly with Armj Topographic Command
(now Defense Mapping Agency Topographic
Center), Washington, D.C.
70 JÖKULL 23. ÁR
GRAVITY TIES TO FOREIGN
BASE STATIONS
Several gravity ties have been made in the
past between Iceland and foreign base stations.
Table 2 summarizes the values obtained for
Reykjavík A from five of these ties. The values
obtained in the 1965 and 1970 connections are
in good agreement with each other. The EASCL
value of 982 279.86 mgal for ReykjavíkA,
which is close to the average of the 1965 and
1970 values, has been used as the reference
value for the present base station network.
SURVEY PROCEDURES AND
FIELD OPERATIONS
All the new base stations have bench marks
with identifying numbers. In a few cases where
the base stations were located at earlier establ-
ished geodetic points, the existing bench marks
were used. In most cases, however, new bench
marks were set up consisting of a copper plate,
3 cm in diameter, bolted on the surface. The
instruments were, when possible, set up with
their footscrews at the level of the bench mark.
This is described in Appendix II as H.I. (height
Fig. 1. Location of gravity base stations estab-
lished in Iceland in 1968. The three secondary
base stations established later are also shown.
Mynd 1. Þyngdarmœlistöðvar i grunnneti 1968.
A kortinu eru einnig sýndar þrjár hjálparmceli-
slöðvar, sem komið var upp seinna.