(£00)
U.S. Department of the Interior 
Geological Survey
Magnetic and Bathymetrie Data from R/V FARNELLA 
Cruise FRNL 85-4 in the Puerto Rico and U.S. Virgin 
Islands Exclusive Economic Zone
by Kathryn M. Scanlon 
Open-File Report 86-399
This report is preliminary and has not been reviewed for conformity with U.S. 
Geological Survey editorial standards. 
Any use of trad* names is for 
descriptive purposes only and does not imply endorsement by the U.S. 
Geological Survey.
1986
Magnetic and Bathymetrie Data from R/V FARNELLA Cruise FRNL 85-4 
In the Puerto Rico and U.S. Virgin Islands EEZ
by 
Kathryn M. Scanlon
Between November 4th and December., 3rd 1985, the U.S. Geological Survey 
in cooperation with Great Britain's Institute of Oceanographic Sciences 
collected over 9500 line kilometers (km) of magnetic and bathymetric data in 
the Exclusive Economic Zone (EEZ) of Puerto Rico and the U.S. Virgin Islands 
(Fig. 1). 
Line spacing was about 37 km in the deep areas (i.e., north of 
about 19°N and south of about 17.5°N) and as close as 10 km in the shallow 
areas near the islands (i.e., between about 17.5°N and 19°N). 
Data were 
collected on the insular slopes north and south of the Islands in water depths 
greater than about 500 meters (m). 
North of the islands, the survey area 
covers parts of the Antilles Outer Ridge and the Puerto Rico Trench; south of 
the islands, it covers parts of the Muertos Trough and the Venezuelan Basin.
The work was conducted aboard R/V FARNELLA on cruise FRNL 85-4.
Navigation data were acquired by an integrated navigation system using 
mainly transit satellites, gyro compass, and doppler speed log. 
Global 
Positioning System (GPS) data were also used during the few hours each day 
when at least three GPS satellites were in range.
The magnetic data were collected using a proton precession magnetometer 
towed about 200 m astern of the ship. 
The total magnetic field and the 
magnetic anomaly (calculated using the International Geophysical Reference 
Field (IGRF) 1985 values for the earth*s field) were both recorded in gammas 
at two-minute intervals.
A 10-kHz towed echo-sounder with a flat-bed wet-paper display was used to 
record bathymetric information. 
Depths were measured on the graphic display 
at six-minute intervals. 
Additional values at two-minute intervals have been 
interpolated on a straight line between measured values.
The original data may be examined at the U.S. Geological Survey, Woods 
Hole, MA 
02543. 
Magnetic tapes of the magnetic data and the digitized 
bathymetry can be purchased only from the National Geophysical Data Center, 
325 Broadway, Boulder, CO 80303, telephone (303)-497-6338.
68'
FARNELLA
1985
LEG 4
'"'.. .-25 "4000m""'"... .._..-  -..
16° -
Figure 1. 
Location map of R/V FARNELLA Cruise FRNL 85-4. 
Thin solid 
lines represent the ship's track along which magnetic and 
bathymetric data were collected. Dotted lines are 
bathymetric contours in meters. Heavy solid line denotes 
the outline of the U.S. EEZ.