Teong Beng Koay

Hardware architecture for a modular autonomous underwater vehicle STARFISH

The use of autonomous underwater vehicles (AUVs) in various research, commercial and military applications has significantly increased in the recent years. Most AUVs available commercially tend to be complex and very expensive. With advances in recent technology, sensors with new functionality or lower cost substitutes have become available. Most existing AUV platforms do not facilitate easy integration of new or upgraded sensors. A solution to this problem is to have a modular AUV system with changeable payload sections capable of carrying different sensor to suite different missions. Modular AUVs are exceptionally useful in group mission scenarios with different AUVs carrying different sensor payloads. By having a team of modular AUVs, payloads can be easily interchanged between the AUVs to configure the team for various missions. Modular AUVs require their sections to be electrically and mechanically compatible with one another. In this paper we describe the detailed architecture of the electronics system for STARFISH AUV. The benefits of modular hardware and its advantages in developing and integrating newer sensor payloads with the base AUV are shown. The modular electronics system for STARFISH AUV has been implemented and currently being tested.

A compact real-time acoustic bandwidth compression system for real-time monitoring of ultrasound

Many animals and systems radiate ultrasound that contains valuable information, from bats to high-voltage power lines. We set out to develop a real-time bandwidth compressor that can convey the prominent features of ultrasound in the human hearing band of 50 Hz to 16 kHz that requires no assumption of where in the ultrasonic frequency band of interest or when in the time domain the information is encoded. A primary application is in dolphin communication, which is believed to be both sophisticated and ultrasonic. Real-time studies of their acoustic communication patterns together with their behavior with the added capability to be able to react and respond in a timely manner to interact with them could rapidly generate important findings, greatly improving the efficiency of dolphin-human interactions. This is not possible without a real-time interface between ultrasound and human hearing. As is well known, there is no pictorial representation that readily conveys the richness of a sound. We are therefore driven to find an efficient acoustic interface, translating ultrasound into audible sounds. This is easy to do in post-processing (simply play back at reduced speed), but continuous streaming real-time processing presents a challenge. The total information-carrying capacity of a signal can be represented by the time-bandwidth product. If the time is constrained to be the same and the bandwidth must be reduced, some information must be discarded. Choosing how and where to do this is the key to a successful algorithm. In this paper we present an algorithm that compresses ultrasound signals into the audio band of human hearing while maintaining the overall signatures and structures of the signal, regardless of the signal type. This algorithm can be demonstrated to be optimal under the applied constraints. This is followed by the design of a prototype system that provides realtime bandwidth compression and a preliminary test result of the system capability. The algorithm has a time-domain implementation that makes it possible to downshift signals sampled at up to 1 MSa/s to audio range using a DSP. The system is autonomous and compact so that it can be carried by operators, including divers, allowing them to swim among dolphins while listening to their communications. The system is demonstrated using high frequency acoustic signals from a bottlenose dolphin

PANDA; a self-recovering shallow water acoustic logger

An increasing focus on monitoring the coastal environment and the need to do so without leaving any surface expression to hinder vessel traffic or attract unintended recovery or collateral damage from other marine activities has led to a several developments in building bottom-mounted observation platforms that release to the surface on command or after a fixed delay. Typically these consist of a pressure housing with internal electronics package, a release mechanism, deadweight anchor, buoyancy unit and perhaps a spooled line. If no line is used, the deadweight is released and left on the bottom. This may be unacceptable in terms of environmental impact and undesirable for other reasons, particularly in sensitive areas. A second major disadvantage is that a free-floating released package drifts with current and can easily be lost. If the package is small (desirable if it is to be cheap and easily deployed and recovered) it is then difficult to see on the surface, particularly in rough seas. Expensive VHF transmitters, GPS receivers, strobes, etc., are then required to ensure pick-up. This drives up the cost. The spooled line approach not only recovers the entire system, but also maintains the package tethered to the bottom at a fixed location until pick-up. With GPS standard positioning now accurate to some 5 in rms, this is sufficient to locate even small packages. We present an inexpensive package design that is small, fight, deployable by two people and that consists only of a single combined buoyancy, pressure casing and spooled line unit plus an anchor. This is a development of an earlier Pop-up Ambient Noise Data Acquisition (PANDA) system built in 1996.

Advanced PANDA for high speed autonomous ambient noise data collection and boat tracking - system and results

Many underwater acoustic recording applications require a high speed data acquisition system that is not contaminated by noise from the support vessel. This calls for autonomous recording system that is self-contained. Many of such systems are either bulky in size such as moored data buoy, or conventional bottom mounted system with acoustic release system; small in data capacity such as miniature acoustic recorder or tags; or needs high maintenance costs such as AUV monitoring. We present an alternative autonomous system that is cost effective, small and provides directivity capability. The Advanced Pop-up Ambient Noise Data Acquisition (A-PANDA) is the next generation underwater acoustic recording system developed by the ARL. The system now has increased CPU power, enhanced sampling rate, increased numbers of channels, digital control, oven controlled real time clock, compass, and highly programmable through a home-built trusted-realtime scheduler. Each A-PANDA has enough data storage and battery capacity to allow deployment periods from tens of hours of continuous recording, to weeks of burst recording. System retrieval can be easily performed through an acoustic release or a pre-programmed time release. A-PANDA can be fully recovered and leaves no anchor or deadweight behind, introducing minimum or no environmental impact to the site of study. A typical deployment procedure involves a small vessel ferrying the A-PANDA to a desired location, deploying the system, leaving the vicinity and returns only for retrieval; hence the acoustic recording is free of self-contamination from the surface vessel. We present work on the use of the A-PANDA to form a random array for the purpose of tracking surface vessels. Since each A-PANDA has a triangular array with three hydrophones, our approach uses high resolution techniques such as the MUSIC algorithm to provide DOA estimations to targets from each A-PANDA. Localization can be achieved by combining the DOA estimations for all of the A-PANDAs. The developed algorithm makes use of cosine packet transforms to identify likely tonal content from surface vessels, prior to MUSIC beamforming, such that only chosen frequencies are beamformed. This reduces the computation, and reduces the clutter in the beamformer output. Finally a Myriad filter is used to track the output of the beamformer over time. When compared against a model based Kalman filter the Myriad filter requires no dynamic model of the surface vessel, and does not have a tracking lag. Simulation results and field trial results to test the DOA estimation performance of a single A-PANDA show a promising tracking performance with an average bearing error of 2 degrees. The maximum range was limited to 650 m due to physical constraints.

Enabling humans to hear the direction of sounds underwater - Experiments and preliminary results

Sound localization by the human auditory system is known to be ineffective underwater. In a research study at the Acoustic Research Laboratory, we introduce additional directional cues from ultra-sonic frequency components. This enables us to work with smaller wavelengths and build simple, small, directional receivers in order to introduce Inter-aural Temporal Differences (ITD) and Inter-aural Intensity Differences (IID) cues to the human subjects. Along with a real-time acoustic bandwidth compression algorithm, we are able to introduce a sense of direction into their hearing in water. The prototype system consists of a pair of directional receivers of less than 60 mm diameter that are spaced and angled in such a way that high frequency directional cues from 20 kHz-200 kHz are created in the audio hearing range, providing a sense of direction. Several experiments have been conducted in a small tank to study the performance of the system. The preliminary results are very promising. Independent tests on the directional receivers show that subjects are able to differentiate direction to within plusmn12 degree 95% of the time. The subjects claim that there was a clear sense of direction in their hearing tests. Results from swimming pool experiments indicate that subjects wearing the prototype system demonstrate capability in direction localization, although the sense of direction seems somewhat reduced compared to the independent tests on the directional receivers. This paper presents the experimental design, and preliminary analysis of the data.

Measuring the augmented sound localization ability of humans in the underwater environment

Humans are poor, if not incapable, at localizing sound underwater due to significant reduction in Inter-aural Temporal Differences (ITD) and Inter-aural Intensity Differences (IID) caused by reduced impedance mismatch and the higher sound speed in water. An improvement in sound localization underwater will significantly enhance divers safety, the way divers perceive and appreciate the underwater environments. A system that augments and enhances the sound localization ability of humans underwater was built for this purpose. The system extracts directional cues from high frequency acoustic component of the received signal and reintroduce the cues in audio band to the diver that wears the system. The novelty of this approach is that it does not need any explicit information on the signals in advance to localize them. The system passes almost the entire signal band to its user with minimum relative distortion except the directional cue ti re-introduced. It is then up to the user to perceive, detect, and localize the sound. In this paper, we present the setup and results from an experiment that measures the localization performance of divers using the system. The experiment setup consists of a source transmitter that was randomly positioned in a contiguous, one-meter radius, semi-circular frame, and a blindfolded subject that attempts to localize the acoustic source. Both the headings of the transmitter and subject were digitally recorded and compared to gauge the localization performance. Experiments have been carried out across different signal to noise ratio and across different frequencies above 20kHz. The result from the experiment shows that a diver using the system was able to localize a source to within ±15 degrees nearly 75% of the time. It is also observed that SNR does not significantly affect the localization performance within the range of SNR that we were testing. The subjects were able to localize acoustic source in a noisy marina environment with the system. The localization performance of the subjects seemed to improve as the subjects gained experience using the system over a few experiment sets. This suggests that the human brain adapts its perception ability and learns to use the new directional cues rather quickly.

Perfomance Evaluation Of A Singal Crystal Hydrophone

Relaxor single crystals such as PZN-PT and PMN-PT exhibit superior electromechanical properties and are touted as the next-generation materials for future high performance piezo devices. This work describes a new hydrophone made of high-sensitivity PZN-PT single crystal d31 sensing elements. Three such elements are mounted in custom-made housing. A compartment is provided to house the three pre-amplifiers, one for each element. In the current prototype each element has its own input. This allows the directionality of each element to be measured and the possibility of locating the source direction from the combined signals of the three elements. A compact low noise high impedance voltage follower pre-amplifier has been designed which provides 26 dB of gain. The overall sensitivity was measured to be -169 dB re 1 V/muPa. Directionality has been measured to be approximately omni-directional within plusmn1 dB, up to a frequency of 7 kHz.