TECHNICAL NOTES AND RESEARCH BRIEFS

R. H. Nichols, Jr. Bell Telephone Laboratories, Whippany, New Jersey 07981

13.11n

"Telesounding" -- Multiple Depth Measurement with a Side-Scan Sonar

K. E. SLAYMAN

O•ce of Naval Research, London, England

Two underwater acousticians--Mr. A. R. Stubbs and Dr. B. S.

McCartney--at the British National Institute of Oceanography (NIO), Wormley, Surrey, England, have developed a method of area-coverage depth sounding from a ship. "Telesounding"--as they call their method--is an adaptation of a hull-mounted, narrow-beamed side-scan sonar to provide depth measurements along a line perpendicular to the ship's track out to the maximum range of the sonar equipment.

The key to their method is the Lloyd mirror, or image inter- ference, effect, in which a pattern in the underwater sound field is caused by alternating constructive and destructive interference between the direct path and the sea-surface-reflected path (if the sea surface is not too rough with respect to the wavelength of the sound). The surface-reflected rays appear as if they originate from a source located at the same distance above the surface as

the actual source lies below the surface. By combining the sound energy arriving from the two sources--actual and virtual--the sound field can be calculated at a given point.

In the "Telesounding" method, which should not be sea-state limited, Stubbs and McCartney have created their own image interference effect by transmitting from two 250-kHz horizontal transducer line arrays vertically separated by a distance equal to that which would exist between a source and the virtual source

if the sea surface were actually being used as a reflector. The transducers are mounted on a roll-stabilized, tiltable plate, located at a known distance well below the sea surface, in the NIO re- search vessel RRS DISCOVERY. By measuring the recorder range--the slant range between the sea bottom at the point of the sounding and the midpoint between the two transducers--and the reflection angle (modified by plate tilt), the horizontal range and the vertical distance between the transducer assembly and the bottom at that range can be calculated by simple sine and cosine relationships. The arguments of the trigonometric func- tions include terms to account for the beam number, the wave- length of the sound, the distance between transducers, and the phase relationship between the two transmissions.

The NIO team has produced actual bathymetric charts from field trials conducted in several shallow water areas (15-50 m) near the British Isles. The charts were made using a 10-m ground spacing (horizontal interval) out to a horizontal range of 200 m. The recorder ranges were measured from the sonar chart recorder by a manually operated tracer with a punchtape output. These ranges were then fed to a computer which solved the trigonometry and plotted the depths at the selected horizontal interval. Maxi- mum depth errors varied between 4-0.3 m in 15 m of water (large sand waves) to 4-1.0 m in 50 m of water (flat bottom). A theoretical investigation showed that recorder range measurement errors are important for horizontal range calculations and •tilt angle determination is important for depth calculations. For

example, at 20 m depth, a 1-m recorder range measurement error provides a ! m range error; and a tilt angle error between 4 and 30 minutes produces a depth error which varies between 0.25 and 1.5m.

Several problem areas--both real and potential--require further study. Among these are the effects of refraction on system ac- curacy, which will be of particular importance in deeper water where the velocity-depth profile may not be iso- or near iso- velocity, and the effects of ship's motions, other than roll, which are not yet fully known (except that heave effects are important and allowance can be made). The Hi-Fix Navigation system used in DISCOVERY had up to a 6-m system error, which is large for a 10-m ground spacing. This problem is not unique to the "Telesounding" method.

In the future, Stubbs and McCartney intend to use a three- transducer array and to conduct phase relationship studies, possibly using more beams than at present. Elimination of sys- tem errors from various sources is also high on the priority list for future work. They also plan further trials with a 36-kHz side-scan sonar--modified for "Telesounding"--which has already been used successfully in water 200 m deep.

"Telesounding" does not provide "blanket" coverage of depth measurements over a given area, but the method can give lines of soundings which are nearly one order of magnitude greater in number than current two-dimensional systems. This can lead to a more efficient use of a survey ship, and consequently save money.

A technical report of this work is in preparation and will be published later this year.

4.4

Two Studies of Children's Hearing The results of studies of children's hearing characteristics have

recently been issued in the following two reports:

1. Hearing and Related Medical Findings Among Children: Race Area, and Socioeconomic Differentials, United States-- Health Services and Mental Health Administration, DHEW, Rockville, Md. 20852 (DHEW Publication No. HSM-73-1604). In this report on the ear, nose, and throat (ENT) findings of children 6-11 years of age, the National Center for Health Statistics presents national estimates showing regional, racial, and socioeconomic differentials in the prevalence of ENT pa- thology and heating problems as determined in the Health Exami- nation Survey of 1963-1965. For this survey a probability sample of 7417 children aged 6-11 years of age was selected to represent the 24 million noninstitutionalized children of this age in the United States. The total of 7119 or 96% of the sample were found to be closely representative of American children of this age with respect to age, sex, race, region, and other selected demographic and socioeconomic variables.

Abnormalities of the eardrum were found about as often, on examination, among white children as Negro children but slightly more frequently among children from the South and those from rural areas. No consistent association was found between the

554 Volume 54 Number 2 1973

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TECHNICAL NOTES AND RESEARCH BRIEFS

presence of such conditions and the socioeconomic status of the family, though the prevalence tended to be slightly lower among those from families in the middle income brackets.

Tonsils were found to be completely or partially removed more frequently among white than Negro children and less frequently among those from the South and those in families with annual family income of less than $5000. Histories of previous ear infec- tion and ear injury were reported more frequently among white than Negro children while trouble hearing, the history item most closely correlated with actual hearing threshold, was cited slightly less often among white than Negro children.

Included are facsimilies of the examination and history forms; description of the survey design and reliability of estimates; and definitions of demographic and socioeconomic terms used in this report.

•Copies of "Hearing and Related Medical Findings Among Children: Race, Area, and Socioeconomic Differentials, United States," VITAL AND HEALTH STATISTICS, Series 11, No. 122, DHEW Publication No. (HSM) 72-1604, 33 pp., may be purchased for 70 cents from the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.•

2. Characteristics of Hearing Impaired Students by Hearing Status, United States: 1970-71--Brenda Raulings, Office of Demographic Studies, Gallaudet College, Washington D.C., March 1973 (Series D, No. 10). Presented in this publication are selected characteristics of approximately 41,000 hearing impaired students who were enrolled in special educational programs during the 1970-1971 school year. Each of the variables is pre- sented in terms of four groupings of students: (1) all students, (2) those students with a better ear average of under 85 dB, (3) those with a better ear average of 85 dB and above, and (4) those for whom a better ear average could not be computed. Included in the report is' information on the students regarding their sex, age, additional handicapping conditions, age at onset and age of discovery of the hearing loss, probable cause of the loss, type of present educational program, parental history of deafness, and distribution according to the states in which they are attending school. The data collection methods, a description of the variables, and the qualifications and limitations of the data are also included in the report.

The Annual Survey of Hearing Impaired Children and Youth is conducted by the Office of Demographic Studies at Galtaudet College. The major source of support is grant funds from the National Institute of Education, Department of Health, Educa- tion and Welfare. The additional funding is provided by Gallaudet College.

[Copies of this report are for sale by the Gallaudet College Book- store, Washington, D.C. 20002.•

10.3; 16.8, 16.9

Ultrasonic Instrumentation for Draining Body Fluids

A novel technique and instrumentation for locating and drain- ing (aspirating) body fluids is described by Professors B. B. Goldberg and H. M. Pollack of the Temple University Health Sciences Center, Philadelphia, Pa., in the January 1972 issue of Radiology (102, 187-189).

The following is excerpted from their paper:

"Ultrasound can easily determine the presence of fluid, whether localized (as in cystic masses and abscesses) or free (as in pleural effusions and ascites). When proper equipment settings are used, fluid will produce no echoes, since ultrasonic reflections occur only at the fluid-solid interfaces which make up the near and far walls of the mass or collection. Since the velocity of sound in tissues is fairly constant, the ultrasonic equipment is calibrated so that the size and depth of a mass or fluid collection can be accurately measured. Ultrasound has been helpful in percutaneous

aspiration of renal cysts as well as in pleural effusions; however, thus far it has been of value only in localizing the fluid, not during aspiration. To overcome this limitation and provide continuous monitoring during the procedure, a special ultrasonic transducer with a central hole was designed. The technique and its applica- tions are discussed below ....

"The modified ultrasonic transducer had a standard frequency of 2.25 MHz with an active element diameter of 0.5 in. A shielded

cable on one side facilitated the drilling of a hole 0.125 in. in diameter. The hole can be made to accommodate a needle of any size. The transducer was fully grounded. Since aspiration almost always required a sterile technique, the transducer was cold- sterilized using the standard ethylene oxide technique. The hole was thoroughly cleaned with a small brush and alcohol following each procedure in order to remove trapped blood or tissue ....

"The base line on the oscilloscope screen was calibrated in millimeters, allowing measurement of the depth and size of the mass or fluid collection. Since it was possible to determine the exact depth of the fluid beneath the skin surface, a needle of the appropriate length could be selected in advance ....

"After the area of interest was cleaned and locally anesthetized, a small amount of sterile water-soluble lubricating jelly was placed on the skin to eliminate trapped air which might otherwise inter- fere with the transmission of the ultrasonic beam. The transducer

was then placed on the skin over the region of interest. The needle was advanced into the body, producing an echo when the tip entered the fluid. The echo arose at the interface between the needle tip and the fluid, allowing the position of the needle in the fluid to be observed continuously. During aspiration of the fluid, continuous ultrasonic monitoring provided information about the size of the decreasing fluid space. It was immediately apparent if the needle tip moved out of the fluid, and repositioning was easily accomplished.

"Unlike fluid-filled masses or collections, it was usually difficult to locate the echo arising from the needle tip in solid tissues, due to the multiple reflections produced at the solid-solid interfaces. However, this technique might still be used for biopsying solid masses. In this case, a mark could be placed along the shaft of the needle at the point determined by the ultrasonic measure- ments, indicating the distance from the skin surface to the center of the mass (the height of the ultrasonic aspiration trans- ducer must also be taken into account). If the needle cannot be easily marked, a ruler can be attached to the transducer. In fact, such a setup was used during the in vitro and in vivo experiments to check the depth indicated by the echo recorded from the needle tip ....

"The development of a specially-modified ultrasonic transducer has made the aspiration of cysts and other fluid collections rela- tively simple and safe. Previously, most aspiration techniques were performed in a hit-or-miss fashion. With this new ultrasonic technique, however, the needle may be accurately guided into the area of interest, and changes in the size of the fluid space during aspiration are known at all times. The ultrasonic aspiration transducer has proved to be useful in theracentesis, paracentesis and pericardiocentesis, as well as in the aspiration of renal cysts. It should also be valuable in suprapubic aspiration of the urinary bladder and in amniocentesis. We are now evaluating its useful- ness in needle biopsy of solid masses."

[The equipment used was an Ekoline 20, Smith Kline Instru- ments Inc., Palo Alto, Calif. 94306.-1

3.1

Technical Translations Available

The following four translations of technical papers are available from the National Technical Information Service, Springfield, Virginia 22151, under the order numbers indicated.

Acoustic Wave Excitation in a Flarne--M. Fitaire and D.

Sinitean [Translation of "Excitation D'Ondes Acoustiques par

The Journal of the Acoustical Society of America 555

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