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Radio
Acoustic Ranging
It
is most economical to do this work during the foggy months of
July and August, when little other work can be done with any degree
of continuity. During the past season RAR work was accomplished
in the early part of the season because of lack of control at
the start of the season for the inshore work. This worked out
advantageously as there was a large area northwest of Cape Sarichef
where ship hydrography could be based on the previously established
control on Akun and Akutan Islands and the triangulation on Unimak
Island.
The
Vincent-type of sono-radio buoy gave very satisfactory results,
returns being received up to 100 seconds, which was as far as
the work extended. One shore station was established at Cape
Sarichef, but strong currents caused water noises through which
it was difficult for the operator to receive the bombs. Late
in the season an offshore buoy, in 40 fathoms, was substituted
but it was lost. The currents were equally strong in that location,
and large islands of floating kelp are prevalent at that time
of the year and it is believed that the watch buoy was towed
under by one of these, causing its collapse and loss of equipment.
A second buoy was later lost during a northwester. The fall
of the year is considered a poor time for RAR, since there is
usually very little calm weather and the rough seas raise the
noise level of the buoys so high and cause so many strays on
both the old and new Fathometers that satisfactory operation
is almost impossible. Also, there seems to be more static at
this time of year. There is considerable interference on the
frequency now in use from a Japanese broadcasting station and
also from a Russian station sending in code. In addition, if
one of the buoys of one ship becomes noisy it interferes with
the reception of all other units. This suggests that some slight
differences in frequencies may be necessary to prevent interference
from noisy buoys which cannot be silenced immediately because
of weather or other reasons.
There
was quite a range in the velocity of sound between spring and
fall, 1462 meters per second in spring and 1476 meters per second
in fall. Difficulties, experienced by the PIONEER and GUIDE,
in the reception of bomb returns, from both shore stations and
buoys, seem to be due to irregular bottom and shoal areas between
the bomb and hydrophone. The water in the Bering Sea was 38
degrees in the spring and yet cast-iron bombs had to be used
to get returns over certain shoals which were only a few fathoms
less than the general depth; but they were of large area. It
is believed in this case that water temperature is of slight
importance in the successful reception of the bomb returns.