When divers search for limpet mines on ship hulls in turbid or dark water, they must resort to tactile examination. Acoustic systems that detect objects in turbid water typically suffer from low resolution, a low image refresh rate, a large size, and/or high power consumption. This paper discusses the design, fabrication, and testing of a small, prototype diver-held sonar that generates near- photographic quality images at a fast frame rate. Its weight in air is 7.7 kg, and it is 100 g buoyant in seawater. It is 18 cm wide, 20 cm high, and 35 cm long, including a 10-cm handle. The sonar sues acoustic lenses made from polymethylpentene to form 64 beams, each of which has a beamwidth of 0.3 degrees yielding a 1.6 cm cross-range resolution at 3-m range. The sector display has a 19.2 degree field of view. The frame rate varies with range, going from 5.5 frame/s at 15 m to 12.5 frames/s at ranges less than 4 m. The sonar consumes 25 W. The internal batteries provide 3 hours of operation between charges. External packs and cabled power provide additional power options. The images are seen on a mask-mounted video display and can also be cabled topside to a video monitor. The sonar operates at 2 MHz and has a maximum range of 15 m. This sonar allows divers to sweep hulls more efficiency and with greater safety than possible with current methods.

Two diver based systems, the Small Object Locating Sonar (SOLS) and the Integrated Navigation and Sonar Sensor (INSS) have been developed at Applied Research Laboratories, the University of Texas at Austin (ARL:UT). They are small and easy to use systems that allow a diver to: detect, classify, and identify underwater objects; render large sector visual images; and track, map and reacquire diver location, diver path, and target locations. The INSS hardware consists of a unique, simple, single beam high resolution sonar, an acoustic navigation systems, an electronic depth gauge, compass, and GPS and RF interfaces, all integrated with a standard 486 based PC. These diver sonars have been evaluated by the very shallow water mine countermeasure detachment since spring 1997. Results are very positive, showing significantly greater capabilities than current diver held systems. For example, the detection ranges are increased over existing systems, and the system allows the divers to classify mines at a significant stand off range. As a result, the INSS design has been chosen for acquisition as the next generation diver navigation and sonar system. The EDMs for this system will be designed and built by ARL:UT during 1998 and 1999 with production planned in 2000.

The development of a wide field of view, dual-frequency acoustic lens sonar system compatible with both diver-held operation and small vehicle installation is described. The lower frequency is for buried target detection while the higher frequency is to provide an imaging/classification capability of non-buried targets. The lower frequency subsystem was fabricated from thin solid disks of polymethylpentene with a focal length of 34.3 cm. The design of this subsystem was evaluated by comparing measured and theoretical beampatterns and by determining the levels of internal reflections from lens surfaces. A measurement was conducted in a very shallow water area to asses the acoustic performance of the lower frequency lens design and to determine the optimum combination of frequency and aperture sizes. This measurement utilized three partially populated lower frequency subsystems with aperture diameters of 20, 25, and 30 cm; partially buried and fully buried targets; and a buried transducer array to determine the coherence of the transmitted signal in the sediment. Results are presented. Future system developments which include the design of the higher frequency subsystem are described.

While laparoscopes are used for numerous minimally invasive procedures, minimally invasive liver resection and ablation occur infrequently. the paucity of cases is due to limited field of view and difficulty in determination of tumor location and margins under video guidance. By merging minimally invasive surgery with interactive, image-guided surgery, we hope to make laparoscopic liver procedures feasible. In previous work, we described methods for tracking an endoscope accurately in patient space and registration between endoscopic image space and physical space using the direct linear transformation (DLT). We have now developed a PC-based software system to display up to four 512 Χ 512 images indicating current surgical position using an active optical tracking system. We have used this system in several open liver cases and believe that a surface-based registration technique can be used to register physical space to tomographic space after liver mobilization. For preliminary phantom liver studies, our registration error is approximately 2.0mm. The surface-based registration technique will allow better localization of non-visible liver tumors, more accurate probe placement for ablation procedures, and more accurate margin determination for open surgical liver cases. The surface-based registration technique will allow better localization of non-visible liver tumors, more accurate probe placement for ablation procedures, and more accurate margin determination for open surgical liver cases. The surface-based/DLT registration methods, in combination with the video display and tracked endoscope, will hopefully make laparoscopic liver cryoablation and resection procedures feasible.

A new high resolution imaging sonar is begin developed for use by swimmers to identify objects in turbid water or under low light level conditions. Beam forming for both the transmit and receive functions is performed with acoustic lenses. The acoustic image is focused on an acoustic retina or focal pane. An acoustic video converter converts the acoustic image to an electronic from suitable for display with conventional electronics. The image will be presented to the swimmer as a heads-up display on the face of his or her mask. The system will provide 1 cm resolution in range and cross range from 1-5 meters from the object. A longer range search mode is being explored. Laboratory prototypes of key components have been fabricated and evaluated. Results to date are promising.

The need for multiple, cost-effective deployment of undersea acoustic mine-field reconnaissance and mine-hunting systems requires the development of light-weight, low-power, high- resolution sonars. These imaging sonars should be portable enough for use in a diver's hands or in a remote imaging sonar on an unmanned undersea vehicle in shallow waters. Under the support of the DARPA Sonoelectronics program, a system that can simultaneously focus many signals using multiple CCD/CMOS, programmable time-delay beamforming circuits connected to a sparsely-populated 2D acoustic array, is being developed. Using this approach, a real-time image could be formed to search for mine-like objects. To make a sparse array practical, the combination of low insertion loss and wide bandwidth performance is critical to realizing acceptable imaging performance with low illumination levels. In this system, a 20 cm diameter 2 MHz sparse array providing a 0.21 degree main beamwidth is proposed. Using this array, a real-time 2D cross-sectional scan of 128 X 128 pixels is achievable with a down-range and cross-range resolution of approximately 1 cm at a range of 3 m. In this paper, the signal-to-clutter ratios as a function of array bandwidth and sparse-array elements placement are presented. Furthermore, the performance of a CCD/CMOS subarray processor will be reported.

The shallow water and very shallow water environment is a very hostile region for sonar operations, however it is still considered one of the best options for mine detection and classification in this region. The water depth and small vehicle size demands that the sonar be small and low power. A conflicting need exists for very high-resolution sonar, which implies a very large aperture, that can discriminate between small mines and natural or benign manmade objects. Resolution cells of approximately 1/16 the size of the targets smallest dimension are generally considered necessary to classify a target with high confidence level and low false classification rate. The synthetic aperture sonar concept can meet the requirement for small size and high resolution. This paper will review the development of the SAS technology at CSS from a simple, single channel first generation SAS to the present real-time dual frequency multi-channel SAS. All these system were designed to be compatible with small underwater vehicles. The SAS signal processing evolved from a very simple delay and sum beamformer to a more complex motion error modulated beamformer. This paper will show images of these systems as they evolved from the earlier 15-cm resolution SAS to the present system producing 2.5 cm and 7.5-cm resolution from a dual high/low frequency SAS, respectively. The present system operates in real-time and has generated the current images using a physical array that is less than 0.6 meters in length and 0.15 meters in height.

For acoustic identification of objects in a littoral environment, there are generally three frequency bands of interest; 1 kHz to 10 kHz, 10 kHz to 100 kHz and 100 kHz to >= 1 MHz, where the selection of these bands is dependent upon the specific Navy mission. This paper will discuss the progress of the Naval Research Laboratory in developing acoustic projector prototypes to address the lower two frequency bands for unmanned underwater vehicle (UUV) and/or autonomous underwater vehicle (AUV) applications. The band of 1 kHz to 10 kHz is currently being addressed sing cymbal flextensional vibrator elements sandwiched in to thin panels. In-air data has shown that high levels of acoustic displacement at low frequencies are possible with these devices while more recent in-water data has verified these expectations. This success has led to modeling and prototyping of similar devices for shallow water regions. The frequency range of 10 kHz to 100 kHz has been investigated for several years where the acoustic projector was originally reported during AeroSense 1998. The result of integrating the NRL broadband projector into the NSWC/Coastal Systems Station synthetic aperture sonar UUV will be presented. This system integration considers the projector as a constant source level over the 10 kHz to 100 kHz band by driving the 100 kHz resonant transducer with an inversely shaped transformed. The presentation will conclude with a discussion of the future development trends in shallow water transducers for AUV and UUV missions.

The Surf Zone Reconnaissance Project is developing sensor for small, autonomous, Underwater Bottom-crawling Vehicles (UBVs) for detection and classification of images and obstacles on the ocean bottom in depths between 0 and 20 feet. The challenge is to exploit many target features by using a suite of small, inexpensive, and low-power sensors. The goal is to enable the UBVs to detect and classify objects on the sea floor autonomously. A unique aspect of the project is that sensing can occur at very short ranges. The goal for detection range is two to four meters, and classification may involve direct contact between the sensor and the target. The techniques under development include mechanical impulse response, surface profiling, magnetic anomaly sensing, pulse-induction sensing, shape tracing, and imaging. Initial studies have confirmed the usefulness of several of these techniques. Specific behaviors, termed microbehaviors, are being developed to support each sensor by exploiting the vehicle's mobility. Project plans for FY99 and FY00 include construction of a prototype sensor suite and collection of a signature database. The database will be used to develop fusion, detection, and classification algorithms that will be demonstrated over the next four years for the Office of Naval Research.

In Phase II of a Small Business Innovation Research (SBIR) contract funded through the Office of Secretary of Defense (OSD), Quantum Magnetics is developing a fieldable room- temperature gradiometer (RTG). The RTG uses an innovative sensor configuration, called the three-sensor gradiometer (TSG), invented at IBM. The TSG affords unprecedented dynamic range that enables detection of signals near fluxgate sensor noise while the system is in motion int eh earth's field. Sensor enhancements undertaken in this Phase II program include: incorporation of ancillary sensors to enable gradiometer balancing in the presence of ambient field gradients; improved feedback linearity and use of a wideband reference fluxgate sensor to reduce motion noise; and improved filter matching between channels. Operational developments in progress include reduction of the sensor electronics package for man-portability and implementation of real-time operating and target localizing software. The Phase II system will be used for land-based operations to locate unexploded ordnance, and the sensor is being integrated with differential global position satellite navigation to locate targets in geographical coordinates. Separately funded programs will adapt the RTG for use by divers or AUVs in finding naval mines and obstacles.

The SBIR Phase I room temperature gradiometer localizer produced by Quantum Magnetics was received and evaluated in late summer of 1997. While still based on IBM's innovative three-sensor gradiometer (TSG), its performance was greatly improved over the original IBM prototype that was evaluated and reported several years prior. This system shows great promise both as a land based ordnance localizer as well as an underwater mine locator for diver or Autonomous Underwater Vehicle applications. The locating software induced both Frahm-Wynn and the newer 'Magnetic and Acoustic Detection of Mines' algorithms, both of which were evaluated against a variety of ordnance type targets. The TSG configuration affords unprecedented dynamic range that enables detection of signals at the fluxgate sensor noise while the system is in motion in the earth's field. Evaluation of the prototype revealed the need for additional positional sensor to enable more precise balancing and localization. Auxiliary sensors investigated were differential Global Positioning System and accelerometers. Localization software incorporating these sensors is reported elsewhere.

Semi-closed circuit underwater breathing apparatus (UBA) provide a constant flow of mixed gas containing oxygen and nitrogen or helium to a diver. However, as a diver's work rate and metabolic oxygen consumption varies, the oxygen percentages within the UBA can change dramatically. Hence, even a resting diver can become hypoxic and become at risk for oxygen induced seizures. Conversely, a hard working diver can become hypoxic and lose consciousness. Unfortunately, current semi-closed UBA do not contain oxygen monitors. We describe a simple oxygen monitoring system designed and prototyped at the Navy Experimental Diving Unit. The main monitor components include a PIC microcontroller, analog-to-digital converter, bicolor LED, and oxygen sensor. The LED, affixed to the diver's mask is steady green if the oxygen partial pressure is within pre- defined acceptable limits. A more advanced monitor with a depth senor and additional computational circuitry could be used to estimate metabolic oxygen consumption. The computational algorithm uses the oxygen partial pressure and the diver's depth to compute O₂ using the steady state solution of the differential equation describing oxygen concentrations within the UBA. Consequently, dive transients induce errors in the O₂ estimation. To evalute these errors, we used a computer simulation of semi-closed circuit UBA dives to generate transient rich data as input to the estimation algorithm. A step change in simulated O₂ elicits a monoexponential change in the estimated O₂ with a time constant of 5 to 10 minutes. Methods for predicting error and providing a probable error indication to the diver are presented.

Through the use of novel imaging devices called Polarization Cameras polarization vision can be attained in underwater environments. Whereas human vision is oblivious to components of light polarization, polarization parameters of light provide an important visual extension to intensity and color. A physical state of polarization can be visualized directly in human terms as a particular hue and saturation, and this paper utilizes such a scheme presenting image of ordinary scenes as never seen before by humans in the domain of Polarization Vision. Metaphorically, humans are 'color blind' with respect to the perception of polarization and even though this does not appear to inhibit human visual performance, we show how polarization vision is a sensory augmentation that can potentially enhance underwater vision for a diver.

The SEAL camera (SEACAM) is a small underwater imaging and ranging device that will provide a number of useful functions for the divers, such as intelligence gathering, limited nigh vision, and providing ranging information for countermining. SEACAM is designed for low-visibility missions, where 'low-visibility' refers to low diver observability, and is not a reference regarding water clarity. The camera, by virtue of the laser wavelength, is specifically made for the low-visibility mission where emission of visible light is undesirable, and is capable of working in conditions of low ambient lighting. SEACAM is a combination of a digital camera and an underwater laser range finder that allows the process range to the target to be measured simultaneously with the image. Given this measured range and the known field of view of the camera, the 'plate scale' of the image can be precisely determined, allowing for accurate estimates of the target dimensions. Upon return from the mission, the image and range data can be downloaded into a computer for rapid distribution. The camera will be magnetically and acoustically qualified for the Mine Countermeasures environment.

This paper present results from a series of preliminary tests to evaluate a scannerless range-imaging device as a potential sensor enhancement tool for divers and as a potential identification sensor for deployment on small unmanned underwater vehicles. The device, developed by Sandia National Laboratories, forms an image on the basis of point-to-point range to the target rather than an intensity image. The range image is constructed through a classical continuous wave phase detection technique which synchronously couples a modulated light source to a gain- modulated image intensifier in the receiver. Range information is calculated on the basis of the phase difference between the transmitted and reflected signal. The initial feasibility test at the Coastal Systems Station showed the device to be effective at imagin glow-contrast underwater targets such as concertina wire. It also demonstrated success at imagin a 21-inch sphere at a depth of 10 feet in the water column through a wavy air-water interface.

As part of the South Florida Ocean Measurement Center in Ft. Lauderdale Florida, a shallow water range with mines has been set up for a series of MCM experiments using the FAU AUVs. The first experiment was conducted December of 1998. The planned objective was to quantify the performance of the Ocean Explorer AUV for mine reconnaissance tasks such as rapid environmental assessment, remote search, remote classification and remote identification of mine like objects both moored in the water column and laying on the sea floor. The primary sensors used for this test were high frequency side scan and ambient light video. In addition, a forward look sonar and a laser line scanner were fielded. A CTD and DVL/ADCP provide environmental data. The AUV first conducted a wide area side scan survey and environmental assessment. The AUV then returned and its data uploaded. Human operators post processed the side scan and manually detected and classified targets. The AUV was then programmed to revisit the targets and perform close in multiple sensor sweeps with side scan and video of each target. Manual post processing and analysis of this data proved sufficient information for more accurate classification and even identification of targets. This paper will present preliminary results of this experiment with likely implications to VSW MCM operations.

The Advanced Marine Systems Lab at FAU has developed a new ultra modular plastic mini AUV for coastal applications including very shallow water MCM. This vehicle is composed of modular injection molded plastic pressure vessels and a cabling system that allows the modules to be rearranged without rewiring bulkheads. The plastic pressure vessels are inexpensive, inherently mass producible, extremely corrosion resistant, and have low magnetic signature. The pressure vessels are small but are sized to fit most standard electronic board standards such as PC104, 3U VME, Compact PCI, STD 32, and even full size PCI. The mini AUV can be anywhere from 4 ft. to 10 ft. in length depending on its mission. A unique feature is the support for hovering capability with optional cross body thruster sections. The vehicle architecture is an adaptation of the Ocean Explorer AUV system and use a LonTalk distributed control network for connecting all sensor and actuator subsystems as smart nodes. The modularity is contained, control, and power makes this vehicle rapidly reconfigurable and easy to repair or upgrade. The small size of this AUV minimize top side support requirements. But because the Mini pressure vessels are still big enough to house most electronics systems almost all the sensor payloads designed for the larger Ocean Explorer AUV can be repacked to fit the Mini. Planned configurations include a rapid environmental assessment and mine reconnaissance package with side scan sonar, video, acoustic modem, Doppler velocity log, altimeter, Doppler current profiler, and CTD. A networkable acoustic modem system has also been developed at FAU and will enable multiple vehicle communications for coordinated multiple vehicle search and survey operations or for remote diver control. 3 AUVs are undergoing development and testing. This paper will present details of the design and construction of the new Mini AUV as well as explores applications to VSM MCM.

Modeling and simulation is an important tool for the evaluation of new concept systems. In particular, new system concepts are being developed for minefield reconnaissance and neutralization using robot vehicles. Also, with an emphasis on low cost, these systems are begin focussed on multi-robot capabilities using fleets of similar and dissimilar vehicles in cooperative behaviors. The problems of operating in the very shallow water areas (VSW) are increased by the action of waves and currents and uneven bottom topography. This paper will discuss the elements of modeling and simulation methodology for the study of system performance analysis in minefield reconnaissance and object mapping in VSW environments. Crawling and swimming vehicles are considered, although the focus is on the first. Vehicle locomotion models are proposed. Wave and current models are discussed by reference to other ongoing research. The modeling of object detection sensors, and vehicle navigation sensor are also given. Using these principles given above, reference is made to the importance of two types of simulator - a graphics based visualization simulator that views the interactive behavior of robots and environmental objects, and a Monte Carlo low resolution simulator that allows the study of system effectiveness. In an example of a VSW operation with crawling vehicles, results are given that illustrates the effect of control logic parameters, on the time it takes to complete the reconnaissance missions. Also, other control parameters are studied including the effect of changes in the detection range of the primary sensor.

Lockheed Martin Perry Technologies (Perry) is currently demonstrating the employment of small inexpensive Autonomous Underwater Vehicles (AUVs) for area reconnaissance and object relation/classification in Shallow Water (SW) and Very Shallow Water (VSW) environments. An MIT Sea Grant Odyssey II AUV, equipped with side-scan sonar and automated on-vehicle sensor processing hardware and software is employed as an area reconnaissance platform, transmitting detection information to a second concurrently-operating inspection-capable. The conjunctive use of each platform's characteristics optimizes search and evaluation of subsea objects. A unique facet of this Cooperating AUV research addresses the employment of the vehicles in an unstructured navigation environment which does not employ any off-vehicle positioning aids in the completion of search and the derivation of revisit coordinates. All navigation and positioning is vehicle based, employing a combination of Global Positioning System coordinates, inertial measurement, and Doppler measured velocity using coordinates and classification information which may contribute to the classification solution which are derived and acoustically transmitted by the Odyssey search AUV, the CETUS intervention AUV dynamically derives and revises plans which optimize its capability to revisit, localize, and classify targets. This program is intended to provide a base measurements of effectiveness using proven existing vehicles and capabilities, and the means to evaluate and demonstrate the advantages of cooperative sensing from multiple platforms for minimum time/maximum coverage of an area which support the goats of rapid area reconnaissance and evaluation. The ultimate goals of this program are to derive an rapidly deployable inexpensive autonomous reconnaissance and intervention capability for SW, VSW environments, supporting and possibly supplanting the use of ships or other manned assets for many dangerous difficult or expensive SW/VSW water tasks.

We describe our work on the development and use of collaborative virtual environments to support planing, rehearsal, and execution of tactical operations conducted as part of mine countermeasures missions (MCM). Utilizing our VR-based visual analysis tool, Cave5D, we construct interactive virtual environments based on graphical representations of bathymetry/topography, above-surface imags, in-water objects, and environmental conditions. The data sources may include archived data stores and real-time inputs from model simulations or advanced observational platforms. The Cave5D application allows users to view, navigate, and interact with time-varying data in a fully 3D context, thus preserving necessary geospatial relationships crucial for intuitive analysis. Collaborative capabilities have been integrated into Cave5D to enable users at many distributed sites to interact in near real-time with each other and with the data in a many-to-many session. The ability to rapidly configure scenario-based missions in a shared virtual environment has the potential to change the way mission critical information is used by the MCM community.

Many of the problems of operating an AUV can be reduced to one of navigation: How accurately do you know where you are. Navigational precision determines the ability to follow track liens,the ability to map a target to world coordinates, and ultimately, even determines the areas where you are willing to operate the vehicle. This paper presents the technique used for long baseline acoustic navigation by REMUS, a low cost AUV developed by the Oceanographic Systems Laboratory of the Woods Hole Oceanographic Institution. Adapting the traditional long base line approach to this vehicle presents a complex problem because it must be low power, low cost, and small in size, and in addition must work in a shallow water environment. The REMUS system uses a single data acquisition system and DSP to interrogate and receive multiple transponders in a sequential manner. It uses spread spectrum technology which reduces the impact of multi-path in the shallow water environment. A moored pair of acoustic transponders whose coordinates are determined using differential or P-Code GPS allow the vehicle to navigate in world coordinates. The DSP minimizes the hardware requirements, thus lowering the associated hardware cost, size, and complexity. This paper describes the techniques used and provides result of this system using frequencies in the 20-30 khz band, giving a range of up to 1500 meters in water 4 meters deep, and also 10-15 khz band, giving a range of up to 7000 meters in waters 14 meters deep.

Datasonics, in conjunction with the French company ACSA, has developed a precise underwater positioning system with multi-user capability. The standard involves deployment of three or four lightweight, low cost buoys, which can be either anchored or drifting, depending on water depth, environmental conditions and mission requirements. Each buoy is equipped with a GPS positioning unit, an acoustic transmitter/receiver, and a 900 MHz non-FCC licensed RF link to a support vessel. Underwater divers, AUVs, or ROVs are equipped with a programmed acoustic modem which transmits a unique coded signal. Different modes of operation are offered. In the basic mode, the position computation is done aboard a surface platform. As an alternative, an acoustic modem can be used, in cases where the underwater mobile needs precise guidance. In such cases, coordinates, heading setting or range and bearing information can be transmitted to the mobile using a downward acoustic link. In the basic mode, each buoy transmits its current GPS position, along with the range and depth of each underwater vehicle or diver, to the support vessel where each vehicle or diver position is computed and displayed. Using a standard DGPS receiver, with acoustic range computation compensated for propagation velocity variation, underwater position computation accuracy approaches that of the surface GPS position accuracy.

Utilizing quasi-static AC magnetic fields as the channel, MISL has developed a group of unique communication, signaling and navigation systems. We refer to this technology as magneto-inductive (MI). The physical properties of magnetic fields enable these system to operate through any natural medium or medium boundary. Working with the US Navy's Coastal Systems Station, MISL has conducted several test and evaluations of MI system components operating in very shallow water, surf zone and beach zone environments.

Much of navy diving is conducted in regions where the visibility is extremely limited, such as the very shallow water/surf zone region. Special sensor, imaging, navigation, and communication technologies are required to enhance a diver's ability to 'see', navigate, and communicate in these regions. These include hand-held sonars, GPS units, acoustic navigation systems, and low-light-level cameras. A visual interface technology is required for the diver to interpret and make use of this enhanced information, which often is a combination of video images, graphical displays, and alphanumeric data. One such technology is a simple underwater display screen. Unfortunately, in many cases underwater display screens can not be seen at all due to the extremely adverse conditions, rendering an enhanced diver sensor systems useless. It remains a considerable technical challenge to provide a diver display system that can be clearly viewed underwater in regions with extremely poor visibility and lighting. The US Navy's Coastal Systems Station, Panama City, Florida has been developing diver display systems, specifically virtual image-head-mounted display (HMDs) systems, for navy divers since 1992. These systems incorporate state-of-the-industry microdisplay technology. This paper will discuss the development of these systems, current status of the technology, and the future outlook for the navy's diver HMDs.

Terrestrial orientation and navigation information is provided by three or more redundant, concordant, veridical, and independent sources of sensory information: the skin- muscle-joint somatosensory system, the inner ear vestibular apparatus, and the visual system. The frequent absence of contact with the bottom and the buoyancy provided by water render the skin-muscle-joint system ineffectual as a reliable source of sensory information. A novel deice, utilizing the intuitive nature of the tactile/haptic system, has been developed to enhance the orientation performance of personnel in sensory deprived underwater environments. The tactile situation awareness system (TSAS) consists of senors providing orientation, guidance, and or communication information to a collection of electromechanical stimulators held in close contact with the skin. In preliminary test, divers equipped with TSAS or traditional visual displays swam a triangular course to evaluate the possible benefits of tactile displays for use in the very shallow water diving environments. The TSAS permitted divers to navigate more accurately and offered information at a lower level of cognitive effort, thereby permitting divers to devote more attention to essential mission-related tasks.