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PACIFIC SCIENCE, Vol. XX, July 1966 
is not necessary to remove the regional magnetic 
gradient to bring out the relatively large mag- 
netic anomalies ranging from 500 to 2,000 
gammas. All anomaly maps were corrected for 
heading errors which, in general, did not ex- 
ceed 40 gammas. 
METHODS AND MATERIALS 
Aircraft and Instrumentation 
Most of the observations were obtained by 
using an Elsec proton magnetometer towed by 
an aircraft. The sea north of Maui over the 
buried extension of the Molokai Fracture Zone 
was surveyed using RV "Teritu” and the U. S. 
Coast and Geodetic Survey ship "Surveyor.” 
Data for other adjacent marine areas had been 
surveyed earlier by the Scripps Institution of 
Oceanography (Arthur D. Raff, personal com- 
munication) and the U. S. Naval Oceanographic 
Office (1962). 
The aircraft used for the program was an 
"E” model of the Stinson L-5 powered by a 
190 horsepower Lycoming 0-435-1 engine. The 
magnetic measurements were made with the 
Elsec magnetometer with a polarization time of 
7 seconds. For the speed of the aircraft, flying 
at approximately 100 miles per hr, this polar- 
ization interval permitted a surface sampling 
interval of 819 ft (250 m). The proton pro- 
cession signal was registered digitally on a dial 
readout and recorded by hand in the aircraft. 
A total of 18,000 miles was flown in check- 
ing out the equipment design, operation, and 
actual data flights. Access doors opened the 
right-hand side of the aircraft fuselage, allow- 
ing stowage of all equipment needed for the 
project. An experimental certificate was ob- 
tained from the F. A. A. on the aircraft to 
permit the opening of the side door in flight 
in order to lower the "bird” which contained 
the magnetometer sensing head over the side 
for trailing behind the aircraft. The Elsec mag- 
netometer with its incorporated power supply 
was placed to the right of the rear seat for oper- 
ation by the observer. The door was closed after 
the 100-ft cable was fully extended. The drag 
induced by the trailing of the bird reduced the 
airspeed by approximately 5 miles per hr. 
The bird was suspended from the aircraft by 
a braided nylon rope through which passed the 
coaxial cable to the magnetometer head. The 
end of the nylon suspension rope was anchored 
to a ring welded to the fuselage structure. The 
bird was designed to be of sufficient size to 
accommodate the rotation of the sensing head. 
Prior to each flight, the head was oriented in an 
east-west direction without regard to the direc- 
tion of the flight lines. The bird was con- 
structed of a hand lay-up of woven fiberglass 
cloth and reinforcing mat with polyester resin. 
The finished laminate was /§ inch thick. Fins 
made of //inch plywood supported the fiber- 
glass-reinforced tail ring. 
Numerous flight tests were conducted to es- 
tablish the suspension point of the bird for the 
best flight characteristics. This point was found 
to be IOI /2 inches aft of the nose. A spoiler 
of triangular cross section was added to the top 
nose surface to decrease the aerodynamic lift 
of the bird. If the bird was suspended at the 
incorrect point, an ever-increasing pendulum 
effect was encountered. The first model of the 
bird proved unstable. This instability was cor- 
rected by lengthening the fins by 4 inches. It 
was necessary to fly during periods when air 
turbulence was at a low level or nonexistent 
in order to obtain valid data. When heavy 
turbulence was encountered, the bird was im- 
mediately retrieved for the safety of the bird 
and the aircraft. During the project, the bird 
was flown at speeds up to 100 miles per hr, and 
on only one occasion during the actual data 
flights did the bird demonstrate any unusual 
flight characteristics. This was during a short 
period of extreme turbulence which occurred 
over the island of Hawaii near Kawaihae. 
Severe pitching resulted before the bird could 
be retrieved into the aircraft. 
Navigational checks and positioning were ac- 
complished by a combination of pilotage and 
dead reckoning. Flight lines were marked on 
topographical maps of a 1/62,500 scale, with 
direct observations being made on surface cul- 
tural and topographical features during the 
flights. On over-sea flights, the track, speed, and 
drift rate were recorded over land and then 
extrapolated over the seaward portion of the 
flight line. Horizontal positioning of any flight 
line of the survey is regarded to be better than 
the order of 500 ft or 150 m. The over-land 
flight lines were spread at 1-mile intervals. 
