operator Jetermined paper-roll size oa the Basis of 2 Cadle Jesisnating signal
arrival times for eaca shot.
These arrival tines were cocputed [roam appreri-
mute shot-to~station distances.
Each paper roll had be\H tine pices every 5
minutes, except during recording of shot signals.
Since analysis requires
synchronacation of station pairs to O.0] second, a single buttcoa vas provided
on the Cime-aark generator which marks calidracions (three-fourths of full Jeflection) at hack times sicultaneously on the four channels of the tev recorders.
The top channe) (Fig. 6.11) on ome recorder (time~oarker peo at the bottca)
records the high-sensitivity trace froa the near head, i.e., the head closest
to the shot; the lower channel records tbe low-sensitivity trace from the far
head.
The other recorder shows the far-head, high-sensitivity crace ia the tca
channe! and the near-bead, low-sensitivity trace ia the lower channel.
This
recorder arrangement provides accurate differences in arrival cises from which
the incidence angles cam be computed.
It was adopted to enable the operator
to observe approxinate travel-time differences on one recorder.
The Johnston Island station maintained one pair of sets (one near, om
far head) on the 12,000-see range, and the other pair (one near, one far bead)
on the 4000-set range.
According to instructions, if the recorded signal froa
Teak exceeded 6 millibars, the operator was to transoit the instructioa UP ONE,
and the otber stations would immediately change cheir lower range aicrobarographs
to the bigher range already on the other sect.
If the recorded signal at Jobnston
Island was less than a 6-millibar amplitude, the operator was to transait the
instruction DOWN ONE, and the other stations would immediately step down the
range settings of their higher sats to agree with the range on the lower range
set.
In the event that Johnston pressures exceeded 34 sillibars, an UP TsO instruction was to be sent.
Stations set on 120 and 400 initially were instructed
to put both secs on 1200 range.
Finally,
if the Johnston recording showed less
than 2 aillibars of pressure anplitude, a DOAN TsO instruction was to be transmicted.
The operators were instructed Co change first the setting farthest froa
set range, then the setting nearest set ranse.
VO”