ALBERT

Description: This is a report of activities supported under Contract NObsr-72521 for the period 1 January through 31 March 1961. It also contains mention of other reports, papers, and undertakings of the submarine geophysics group (listed under "Personnel") which are believed to be of interest to the Bureau of Ships. During this period no cruises have been supported directly under this contract. Eight members of the group under the leadership of Dr. Voorhis have participated in a cruise of CHAIN to the Romanche Trench. Their principal objective was to determine the sill depth which controls the exchange of deep, cold water ,between the western and eastern sides of the Atlantic Ocean. This sill was previously identified from hydrographic evidence to lie somewhat east of the Romanche Trench. A second objective was to continue the observations of temperature structure near the sea's surface with the thermistor chain. Another group, under Mr. Baxter's leadership, continued a sound transmission study in the Bermuda area in support of Project ARTEMIS. A third group, under Dr. Hays's direction, commenced a finely detailed bathymetric survey of an area of special interest to Project ARTEMIS. In all three of these studies we are making use of one or more experimental techniques in the use of sonobuoys, underwater acoustic navigation for submerged instruments, and sound coherence studies which are planned for use eventually in sound transmission and bottom reflection research under this contract.

Description: Bureau of Ships Under Contract NObsr-72521

Description: Research at sea during this three month period, supported by Contract NObsr-72521, was carried out mostly during the latter portion of the CHAIN Cruise 21 to the eastern Mediterranean. Near-surface sound transmission runs were made with the aid of two foreign ships in the eastern Mediterranean and Tyrrhenian Sea. Sound velocity measurements were made there also. Reverberation and back-scatter measurements using half pound explosives as sound sources were recorded on magnetic tape for future analysis. Further, at several places during the cruise acoustic reflectivity of the sea-floor was measured by means of a semi-automatic system employing the Precision Graphic Recorder and the Edo UQN Echo Sounder. Research other than that on CHAIN Cruise 21, included ambient noise studies of recorded signals from finback whales, and analysis of data from previous observations at sea.

Description: The Bureau of Ships Under Contract NObsr - 72521

Description: Experiments are described to demonstrate a new method of sonic signalling at extremely long ranges in the oceans, utilizing the natural sound channel. Signals were made by causing a four pound charge of TNT to explode at about 4000 feet depth. These signals have the following qualities: (a) Extremely long range transmission (probably 10,000 miles). (b) Signal is positively identifiable. (c) Abrupt termination of the signal allows the arrival time to be read with an accuracy better than l/20th second. This permits location of source to better than a mile, if the signal is received at three suitably located stations. (d) The signal duration is related in such a way to the distance that the distance may be estimated to 30 miles in 1000 from reception at a single station. The limitations are: (a) It is required that the great circle path which the sound follows between source and receiver lie entirely in deep water (probably at least 1000 fathoms). (b) Sound travels in water at a speed of roughly 1 mile per second so that the interval between the origin of the signal and its reception becomes sufficiently great to be a handicap for some uses, particularly with aircraft. The signals were received to distances up to 900 miles. Two receiving arrangements have been used, a hydrophone hung 4000 feet over the side of a ship which was hove to, and a shore connected. hydrophone which lay on bottom 4000 feet deep. Extrapolation of the results indicate a range of at least 10,000 miles from this size charge. Recommendation is made to utilize a network of monitoring stations to locate planes, ships, and life rafts in distress on the open oceans. Three or more stations receiving a signal could locate the source better than one mile.

Description: Con tract NObs - 2083, Formerly OEM: sr - 31

Description: Late in 1955 the Deep Water Propagation Committee recommended procurement of 10 sets of sound analysis equipment to be distributed to laboratories working in the field of underwater acoustics. This recommendation was made to be one of the objectives of Contract Nonr-2129. The equipment, including filters for spectrum analysis, was to compute the time integral of the square of the filter output voltages as discussed by Officer and Dietz (1953), WHOI Ref. No. 53-46. In view of the fact that correlation studies are becoming more important it was recommended that the equipment have an optional mode of operation in which it could compute the time integral of the product of two voltages. Multichannel computers were recommended because analysis of data from one hydrophone for one frequency band at one time is much too slow in view of the large amount of data to be processed. Eight channels per computer were chosen because this is the largest number available in standard direct-writing recorders.

Description: Undersea Warfare Branch, Office of Naval Research, under Contract Nonr- 2129(00) (NR 261-104).

Description: This is a progress report of the Institution's research between April and 30 June 1961 supported under Contract NObsr-72521 with the Bureau of Ships, Navy Department. The program consists of studies of compressional wave transmission (sound and seismic waves) through sea water and the underlying earth's crust, the ambient noise of the ocean, and the scattering of sound in the sea and beneath the ocean floor. During the present reporting period sound transmission studies have included laboratory analysis of data taken previously in a continuing program directed toward describing near-surface transmission into the shadow zone, and toward accounting for the variability of near-surface . transmission under nominally "good" sonar conditions . Seismic studies consisted of analysis of seismic refraction data taken two years ago in: the Mediterranean, completion of a report of a seismic reflection study of the southern part of Narragansett Bay, extension of this latter study into Rhode Island Sound, and a series of new measurements of the apparent reflectivity of the bottom at 12 kcps. In the sound-scattering program we accepted delivery of a small towed fish containing sound gear for scattering experiments over near-horizontal paths. This instrument was taken to sea on CHAIN for initial testing and self-noise measurements. A series of tests of new sound sources, supported under Contract Nonr-1367, have demonstrated that seismic reflection observations can be made in deep ocean basins from a ship underway slowly using only such electrically-powered sources as Thumper or Sparker. Sub-bottom structures have been mapped in fine detail experimentally in water over 2600 fathoms deep. This work was done with a Thumper having a 5000-joule electrical input . Plans have been made for increasing the electrical input of Thumper to about 13, 000 joules and Sparker to 25, 000 joules. We plan to use these new sound sources in sound transmission experiments this summer and fall in the Mediterranean Sea. As an extra-curricular hobby Miss Broughton, a technical assistant at the Institution, made interesting magnetic tape recordings of the sounds of a small pilot whale stranded on a local beach. She held microphones on the whale's head near the blow hole. The recorded sounds are rather different from those heard through the water near pilot whales. These and other parts of our work are detailed below.

Description: Bureau of Ships Under Contract NObsr-72521

Description: This manual describes the objectives, design, operation, and maintenance of the Precision Graphic Recorder (PGR), emphasizing its application to echo-sounding. The words "precision graphic recording" describe a method for displaying data by means of successive, precisely-timed rectilinear sweeps of a recording point or "stylus" across a long, moving strip of sensitized paper (Veatch and Smith, 1939, p. 61-63). The recorded data appear as dye-markings, shaded in proportion to signal amplitude along the sweep of the moving recording point.

Description: The Bureau of Ships Under Contract NObsr-72521 and Office of Naval Research Under Contract Nonr-1367 (00) (NR-261-102)