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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.