Navy Divers Research Articles

Time domain beamforming ASIC for a handheld bistatic imaging sonar system

A high-resolution, handheld imaging sonar system has been developed by Teratech Corporation for the U.S. Navy. This is a 192-channel, dual-frequency bistatic sonar for Navy divers performing search and survey missions for underwater explosives. The goal is to provide the most compact and energy-efficient imaging system for the divers. The low power and small volume are a result of the development of Teratech’s Charge Domain Processing (CDP) technology. This technology has led to the development of a low-power 64-channel beamformer chip. As a result, only three beamformer chips are needed for the 192-element array. Until now, implementation of small, low-power sonar systems containing this many elements and forming enough beams to create an image was considered impossible. Test results and acoustic images obtained in Teratech’s acoustic test tank will be presented. [Work sponsored by ONR and OSD Small Business Innovative Research Program, Program Manager, Mr. Bruce Johnson, Naval Explosive Ordnance Disposal Technology Division.]

Collective and Individual Consciousness in Testimonies of Navy Divers

Sick Israeli Navy divers, who were exposed to chemical sewage during their army service, suspected that this exposure was the cause of their cancer. The divers appealed to the courts and demanded the establishment of an independent committee for the investigation of this issue. This step created strong emotional tension between the sick divers and their former brothers-in-arms from the navy. The aim of this paper is to describe the process by which the tension between the divers' individual and collective consciousness is discursively elaborated in their testimony to the committee. This testimony is described by means of a Bakhtinian/Volosinovian semiotic analysis.

Development of a handheld bistatic imaging sonar system for underwater search and survey

A high resolution, handheld imaging sonar system is under development by Teratech Corporation for the U.S. Navy. This is a 192 channel, dual frequency bistatic sonar for Navy divers performing search and survey missions for underwater explosives. Our goal is to provide the most compact and energy efficient imaging system for the divers. The system consists of a self-contained handheld unit and a head mounted display integrated into the divers mask. The low power and small volume are a result of the development of Teratechs Charge Domain Processing (CDP) technology. This technology has led to the development of a low power 64-channel beamformer chip. As a result, only three beamformer chips will be required for the 192 channels. Until now, the implementation of small, low power sonar systems containing this many elements and forming enough beams to create an image was considered impossible. Progress in the development of this product will be presented. In-water testing is planned for late summer 2003. Experimental results and test images available will be presented at the conference. [Work sponsored by ONR and OSD Small Business Innovative Research Program, Program manager, Mr. Bruce Johnson, Naval Explosive Ordnance Disposal Technology Division.]

Underwater loudness for pure tones: Duration effects

The loudness of underwater pure tones was measured by loudness matching for pure tones from 100 to 16,000 Hz. The standard was a one second tone at 1000 Hz. The signal duration was varied from 20 milliseconds to 5 seconds. Subjects were instructed to match the loudness of the comparison tone at one of the test frequencies to the loudness of the standard tone. Loudness was measured at the threshold, the most comfortable loudness, and the maximum tolerable loudness. The intensity of the standard was varied randomly across the test series. The subjects were bareheaded U.S. Navy divers tested at a depth of 3 meters. All subjects had normal in-air hearing. Tones were presented to the right side of the subject from an array of underwater sound projectors. The sound pressure level was calibrated at the location of the subject’s head with the subject absent. Loudness increased and threshold decreased as duration increased. The effect was greatest at the lowest and highest frequencies. The shape of the loudness contours across frequency and duration derived from these measurements are different from in-air measurements. [Research supported by ONR.]

Experimental results for a prototype 3-D acoustic imaging system using an ultra-sparse planar array

A handheld high resolution sonar has been under development to provide Navy Divers with a 3-D acoustic imaging system for mine reconnaissance. An ultra-sparse planar array, consisting of 121 1 mm×1 mm, 2 MHz elements, was fabricated to provide 3-D acoustic images. The array was 10 cm×10 cm. A full array at this frequency with elements at half-wavelength spacing would consist of 16<th>384 elements. The first phase of testing of the planar array was completed in September 2001 with the characterization of the array in the NUWC Acoustic Test Facility (ATF). The center frequency was 2 MHz with a 667 kHz bandwidth. A system-level technology demonstration will be conducted in July 2002 with a real-time beamformer and near real-time 3-D imaging software. The demonstration phase consists of imaging simple targets at a range of 3 m in the ATF. Experimental results obtained will be reported on. [Work supported by the Defense Applied Research Project Agency, Advance Technology Office, Dr. Theo Kooij, Program Manager.]

Loudness for tone underwater

The loudness for pure tones was measured by loudness matching for 1-s pure tones from 100 to 50<th>000 Hz. The standard tone was 1000 Hz. Subjects were instructed to match the loudness of the comparison tone at one of the test frequencies to the loudness of the standard tone. The standard was presented at one of five sound pressure levels (SPL) for each set of frequencies. The standard SPL was varied randomly across test series. The subjects were bareheaded US Navy divers tested at a depth of 3 m. All subjects had normal hearing. The tones were presented to the right side of the subject from an array of underwater sound projectors. The SPL was calibrated at the location of the subject’s head with the subject absent. The loudness increased more rapidly as a function of standard SPL at mid-frequencies than at either high or low frequencies. The most compact loudness contours (least SPL change across range of standard SPL) were at 50<th>000 Hz. The underwater loudness contours across frequency are significantly different from in-air measurements and have a minimum in the 1000 Hz region rather than the 2–4 kHz region observed for in-air measurements. [Work supported by ONR.]

Underwater loudness for tones

The loudness for pure tones was measured by loudness matching for 1-s pure tones from 100 to 50<th>000 Hz. The standard tone was 1000 Hz. Subjects were instructed to match the loudness of the comparison tone at one of the test frequencies to the loudness of the standard tone. The standard was presented at one of five sound pressure levels (SPL) for each set of frequencies. The SPL was varied randomly across a test series. The subjects were bareheaded U.S. Navy divers tested at a depth of 3 m. All subjects had normal hearing. The tones were presented to the right side of the subject from an array of underwater sound projectors. The SPL was calibrated at the location of the subject’s head with the subject absent. The loudness increased more rapidly as a function of standard SPL at mid-frequencies than at either high or low frequencies. The most compact loudness contours (the least SPL change across the range of standard SPL) were at the highest frequency. Loudness contours across frequency derived from these measurements are significantly different from in-air measurements with minimum audibility in the 1000 Hz region rather than the 2–4 kHz region observed for in-air measurements.

Sparse array technology for 3-D sonar imaging systems

A three-dimensional sonar imaging system is under development for use by Navy divers for mine-field reconnaissance and mine-hunting systems. Divers require a small, low-power, lightweight acoustic imaging system with high resolution for examining and disposing of underwater ordinance. Sparse array technology is investigated to develop a sonar requiring the minimal number of signal processing channels while maintaining the beamwidth and sidelobe structure required for high-resolution imaging. Beamwidth and sidelobe structure are examined as a function of transducer element count, channel bandwith, and element location when optimized using various cost functions. Locally optimum solutions are computed for uniformly weighted sparse arrays. Cost functions evaluated for the optimization process compute average sidelobe energy, peak sidelobe energy and a weighted average sidelobe energy. Images will be formed using multiple CCD/CMOS time-delay beamforming circuits to compute the large number of beams required to provide a real-time high-resolution image.

Functional and high-resolution computed tomographic studies of divers' lungs.

Several cross-sectional studies have described a decrease in the expiratory flow rates of divers. The objective of this study was to determine whether the combined application of high-resolution computed tomography (HRCT) and lung function testing supports the reported development of small airway obstruction in divers. Thirty-two navy divers, 27 commercial divers, and 48 referents matched for age and smoking history underwent pulmonary function testing and HRCT of the lungs supplemented by a limited number of expiratory scans. The commercial divers were older and dived longer than the navy divers. Multivariate regression analysis was used to assess the relevant correlations of age, height, pack-years of cigarette smoking, and indices of diving exposure with lung function parameters. The inspiratory vital capacity and forced vital capacity (FVC) were greater, while the FEV% [(100 x FEV10)FVC] and maximum expiratory flow (MEF) at 25% (MEF25) of the FVC were lower for the navy divers than for the referents. The lung volumes and expiratory airflow pattern did not differ between the commercial divers and the corresponding referents. The forced expiratory volume in 1 second (FEV10), FEV%, MEF75, and MEF25 correlated negatively with the years of diving experience. This association was independent of age, height, and pack-years of cigarette smoking. For the majority of the divers and referents the expiratory HRCT revealed minor lobular air trapping without any difference between the groups. The HRCT did not show relevant morphologic abnormalities of small or large airways. The data confirm that diving may affect pulmonary function. However, there is no radiologic evidence for the development of small airway disease in these 2 subgroups of divers.

Speech intelligibility assessment in a helium environment. II. The speech intelligibility index.

The Speech Intelligibility Index (SII) was measured for Navy divers participating in two saturation deep dives and for a group of nondivers to test different communication systems and their components. These SIIs were validated using the Speech Perception in Noise (SPIN) test and the Griffiths version of the Modified Rhyme Test (GMRT). Our goal was to determine if either of these assessments was sensitive enough to provide an objective measure of speech intelligibility when speech was processed through different helmets and helium speech unscramblers (HSUs). Results indicated that SII values and percent intelligibility decreased incrementally as background noise level increased. SIIs were very reliable across the different groups of subjects indicating that the SII was a strong measurement for predicting speech intelligibility to compare linear system components such as helmets. The SII was not useful in measuring intelligibility through nonlinear devices such as HSUs. The speech intelligibility scores on the GMRT and SPIN tests were useful when the system component being compared had a large measurable difference, such as in helmet type. However, when the differences were more subtle, such as differences in HSUs, neither the SPIN nor the GMRT appeared sensitive enough to make such distinctions. These results have theoretical as well as practical value for measuring the quality and intelligibility of helium speech enhancement systems.

Posttraumatic stress symptoms among U.S. navy divers recovering TWA flight 800.

Leffler, Christopher T. M.D.1; Dembert, Mark L. MC, USN, M.D., M.P.H.2 Author Information

Salient Personality Characteristics among Navy Divers

This study evaluated the personality characteristics of U.S. Navy divers. Seventy-two active duty Navy divers completed the Million Index of Personality Styles. The sample strongly showed the traits of Enhancing. Modifying, Individuating, Thinking, and Controlling. The results are discussed in terms of adaptation to the environmental demands of military diving. Suggestions for further research are offered.

Exposure guidelines for Navy divers exposed to low-frequency active sonar.

A 30-month experimental and modeling study was conducted into the effects of low-frequency active (LFA) sonars on Navy divers. 453 dives using 87 subjects were completed with one symptomatic event. A variety of dive equipment, depths to five atmospheres, and three signal waveforms were used. Interim guidance for exposure to LFA signals was issued by the U.S. Navy Bureau of Medicine and Surgery. For exposures to nonimpulsive waterborne sound in the frequency range 160–320 Hz, the following set of parameters did not compromise the safety of a highly trained, fit, and informed diver (diver compromise refers to a diver who could become a casualty or burden to others in an operational setting): A maximum overall SPL of 160 dB for no more than 100 s continuous exposure on a 50% duty cycle, with a cumulative exposure limit of 15 min/dive-day, a total of 9 days of exposure in a 2-week period. SPL is measured at the diver’s location. This guidance is generalizable only to those populations equivalent in medical health and fitness to U.S. Navy divers. [Work supported by U.S. Navy.]

A Model for Predicting Central Nervous System Oxygen Toxicity from Hyperbaric Oxygen Exposures in Humans

Under certain circumstances, Navy divers breathe 100% O2 when working underwater. Serious symptoms of central nervous system (CNS) O2 toxicity can develop from hyperbaric O2 exposure; immersion and exercise are also known to exacerbate toxicity. We developed risk models for quantitative prediction of the probability of developing symptoms using a large set of human data in which occupational exposure conditions were simulated. Exposures were 5 to 265 min at PO2 levels from 20 to 50 feet of sea water (fsw) (1 fsw = 3.06 kPa). Approximately half of the exposures were to a single PO2, while the remainder were more complicated consisting of exposures to multiple levels of hyperbaric O2. In 688 trials, there were 42 exposure-stopping symptoms. We used maximum likelihood to estimate parameters, likelihood ratios to compare model fits, and chi 2 tests to judge goodness-of-fit of model predictions to observations. The modeling shows that risk has a steep PO2 dependence. A model with autocatalytic features fits the data as well as a simpler model: when PO2 is elevated beyond 34 fsw, risk accumulates rapidly without bound while accumulating toward an asymptote at lower PO2 levels. This autocatalytic feature of risk accumulation implies a testable hypothesis that substantial protection from human CNS O2 toxicity can be obtained from intermittent exposure (periodic exposure to lower PO2). The models predict that the probability of O2 toxicity is less than 7% with current Navy limits while breathing 95% O2. Probability of symptoms is < 1% if FIO2 is maintained at the United States Navy recommended level of 75%.

Speech intelligibility assessment in a helium environment

The purpose of this study was to compare the appropriateness and effectiveness of the speech perception in noise (SPIN) test and the Griffiths version of the modified rhyme test (GMRT) in assessing Navy divers' speech understanding using communication systems containing different helium speech unscramblers (HSUs), one of which produces, by subjective observations, more intelligible output than the other. Divers participating in a saturation deep dive and a group of nondivers using digital audio tape recordings of the stimuli used by the divers were tested. Mean percent correct scores on the SPIN and GMRT lists within two listening conditions (taped, topside-diver and live-voice, diver-diver) were almost identical. Listeners scored better on both tests in the topside-diver condition than in the diver-diver condition. The majority of the SPIN errors were on low-predictability items that are void of context. Context clearly played a role in measuring the performance of these subjects, at least for the SPIN test. No significant differences were measured between the two HSUs, although a trend was seen favoring one HSU over the other for the divers. These results have theoretical as well as practical value for measuring the quality and intelligibility of helium speech enhancement systems.

Studies in oral galvanism: mercury and copper levels in urine, blood and saliva in submerged electrically cutting divers.

The aim of the study was to analyse the concentration levels of mercury and copper in urine, blood/blood plasma and saliva in relation to intra-oral electrical activity. Five Swedish Navy divers took part in the study in order to determine whether working submerged with electrical cutting equipment produced changes in the presence and level of oral galvanism and whether this posed a serious occupational health risk. The investigation concluded that the risk of seriously increased intra-oral electrical activity during welding or cutting activities was small. Development of the study is suggested, with long-term sampling of urine and blood samples of divers supported.

Barodontalgia and Barotrauma in the Human Teeth: Findings in Navy Divers, Frogmen, and Submariners of the Federal Republic of Germany

From 2,580 submariners, divers, and frogmen, 13,618 individual findings were evaluated from a total of about 50,000 dental findings of the Nautical Medical Institute of the German Navy, Kiel, West Germany. Trend analysis and statistical significance tests showed that the teeth of navy divers and frogmen had deteriorated very much more within a period of 9 years after their first dental examination than those of submariners. This negative tendency was verified through additional direct comparison between 37 navy divers and 37 submariners whose dental states were observed during a period of 10 years. Here as well, navy divers had significantly worse teeth. The cause of this distinctive dental deterioration among navy divers is probably due to the additional barometric stress they were subjected to for many years during their diving career. Delayed damages as a result of barotrauma may be assumed, a logical suspicion which should be verified by further scientific research.

Personality characteristics of US Navy divers*

Several personality measures, assessing sensation‐seeking, socialization, locus of control, and trait anxiety, were administered to a representative sample of US Navy divers and the results compared to data obtained from published norms. The divers had significantly lower Internality‐Externality scores, were more poorly socialized, and had lower levels of trait anxiety than the norm groups. Findings for the five subscales of the sensation‐seeking measure showed that, compared to the norm group, divers scored significantly higher on the Thrill and Adventure Seeking subscale and significantly lower on the Experience Seeking and Disinhibition subscales. These findings correspond well to constructs of diver personality derived from earlier research. While the data indicate that these measures may be useful in screening and selecting personnel for hazardous occupations, future research should determine the reliability of these differences using appropriate comparison groups (e.g. non‐diving Navy personnel). Inasmuch as moderate correlations were found among the five subscales of the sensation‐seeking measure, the statistical independence of these subscales should be revalidated prior to using these subscales for screening and selection purposes.

Knobology Underwater

Fifteen knobs representing types which might be used underwater were subjected to an experimental comparison to determine what types most enhance speed or accuracy of knob adjustment. Six U.S. Navy divers adjusted the knobs underwater while wearing diving gloves in a variety of temperatures, pressures, and diving equipment. Adjustments were made with emphasis on speed or accuracy at each of three positions on the divers. Results indicate that large diameter knobs can be adjusted underwater more rapidly and accurately than smaller knobs, and that some types of tactile markers enhance accuracy of knob adjustment underwater.

Acute decompression sickness: 50 cases.

In a review of the most recent 50 consecutive cases of acute decompression sickness in US Navy divers undergoing training at the Naval School, Diving and Salvage, in no instance was recompression following the initial treatment necessary, nor was there any permanent morbidity post-treatment. Factors common to this series are 1) strict physical screening and conditioning; 2) physician and diver awareness of the signs and symptoms of decompression sickness; 3) short surface interval between symptom onset and recompression; 4) aggressive diagnostic and therapeutic use of hyperbaric oxygenation, and 5) judicious use of adjunctive measures such as intravenous fluid and dexamethasone (Decadron). In the ideal management, the physician sees the patient shortly after symptom appears. As soon as central nervous system involvement appears, 100% oxygen by mask is administered and the patient is recompressed supine to 60 feet of sea water.