Matthias Hoffmann-Kuhnt

AquaOptical: A lightweight device for high-rate long-range underwater point-to-point communication

This paper describes AquaOptical, an underwater optical communication system. Three optical modems have been developed: a long range system, a short range system, and a hybrid. We describe their hardware and software architectures and highlight trade-offs. We present pool and ocean experiments with each system. In clear water AquaOptical was tested to achieve a data rate of 1.2Mbit/sec at distances up to 30m. The system was not tested beyond 30m. In water with visibility estimated at 3m AquaOptical achieved communication at data rates of 0.6Mbit/sec at distances up to 9m.

Seeing through sound: dolphins (Tursiops truncatus) perceive the spatial structure of objects through echolocation.

Experiment 1 tested a dolphin (Tursiops truncatus) for cross-modal recognition of 25 unique pairings of 8 familiar, complexly shaped objects, using the senses of echolocation and vision. Cross-modal recognition was errorless or nearly so for 24 of the 25 pairings under both visual to echoic matching (V-E) and echoic to visual matching (E-V). First-trial recognition occurred for 20 pairings under V-E and for 24 under E-V. Echoic decision time under V-E averaged only 1.88 s. Experiment 2 tested 4 new pairs of objects for 24 trials of V-E and 24 trials of E-V without any prior exposure of these objects. Two pairs yielded performance significantly above chance in both V-E and E-V. Also, the dolphin matched correctly on 7 of 8 1st trials with these pairs. The results support a capacity for direct echoic perception of object shape by this species and demonstrate that prior object exposure is not required for spontaneous cross-modal recognition.

Possible age-related hearing loss (presbycusis) and corresponding change in echolocation parameters in a stranded Indo-Pacific humpback dolphin

SUMMARY The hearing and echolocation clicks of a stranded Indo-Pacific humpback dolphin (Sousa chinensis) in Zhuhai, China, were studied. This animal had been repeatedly observed in the wild before it was stranded and its age was estimated to be ~40 years. The animals hearing was measured using a non-invasive auditory evoked potential (AEP) method. Echolocation clicks produced by the dolphin were recorded when the animal was freely swimming in a 7.5 m (width)×22 m (length)×4.8 m (structural depth) pool with a water depth of ~2.5 m. The hearing and echolocation clicks of the studied dolphin were compared with those of a conspecific younger individual, ~13 years of age. The results suggested that the cut-off frequency of the high-frequency hearing of the studied dolphin was ~30–40 kHz lower than that of the younger individual. The peak and centre frequencies of the clicks produced by the older dolphin were ~16 kHz lower than those of the clicks produced by the younger animal. Considering that the older dolphin was ~40 years old, its lower high-frequency hearing range with lower click peak and centre frequencies could probably be explained by age-related hearing loss (presbycusis).

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.

Acoustics of shape recognition by a dolphin in a cross‐modal matching‐to‐sample paradigm

A pacific bottlenose dolphin was trained in a two‐alternative cross‐modal matching‐to‐sample paradigm. The animal was able to inspect complex PVC‐pipe shapes through echolocation or vision but never through both senses simultaneously. Acoustic data was collected through a 3‐channel high‐frequency recording system while the dolphin performed one of the following tasks: (1) match a complex shape with its sonar only (pure echoic matching), (2) match from vision to echolocation and (3) match from echolocation to vision. Simultaneously, synchronized in‐air and underwater video was recorded documenting the approach path of the dolphin to either the sample object or to the alternative objects. The collected data was analyzed for type of click signals used, the frequency range of the emitted clicks, number of clicks emitted before a successive match and variations of click type with different objects.

Implications of the variety of bat echolocation sounds for understanding biosonar processing

The variety of echolocation sounds used by different species of bats have implications for target ranging. Signals recorded at individual sites reveal species stacked in different frequency bands, perhaps to avoid cross-interference. Search-stage signals include short single-harmonic or multi-harmonic tone-bursts, or very shallow FM bursts. These narrowband sounds have abrupt onsets to evoke phasic on-responses that register echo delay, but with limited acuity. Wider FM sweeps used for searching by other bats evoke on-responses at many more frequencies for better delay acuity. These sound types may signify foraging in the open, within broad spaces bounded relatively remotely by trees or the ground. Intervals between broadcasts are consistent with biosonar operating ranges set by the boundaries of the scene in relation to atmospheric attenuation. Most species make transitions to wider signal bandwidth during interception by increasing FM sweep-width or adding harmonics. Additionally, wideband, multi-harmon...

Dolphin target detection processes investigation using finite element model

Dolphins and porpoises use their sophisticated biosonar systems for targets detection, within a range of a few meters to about 200 m, there is not a better sonar on the planet. In this study, the high resolution computer tomography (CT) scan data were used to create the detecting click signal propagation models of Atlantic bottlenose dolphins (Tursiops truncatus) and harbor porpoise (Phocoena phocoena). The finite element methods (FEM) were used to simulate the processes of the clicks emitted from phonic lips and transmit to the water through animals’ heads. The biosonar beam forming in the nearfield and farfield including the amplitude contours were determined and compared to the prior measurement results. There were no evidences of convergence in the farfield, which were consistent with measurement results for Tursiops truncatus. Additionally, in a cross-modal matching experiments with Tursiops, we found that the accuracy of the successive match was significantly different when the following subjects wi...

Likely Age-Related Hearing Loss (Presbycusis) in a Stranded Indo-Pacific Humpback Dolphin (Sousa chinensis)

The hearing of a stranded Indo-Pacific humpback dolphin (Sousa chinensis) in Zhuhai, China, was measured. The age of this animal was estimated to be ~40 years. The animals hearing was measured using a noninvasive auditory evoked potential (AEP) method. The results showed that the high-frequency hearing cutoff frequency of the studied dolphin was ~30-40 kHz lower than that of a conspecific younger individual ~13 year old. The lower high-frequency hearing range in the older dolphin was explained as a likely result of age-related hearing loss (presbycusis).

Dolphin echolocation—synthetic aperture or “raster scanning”?

A bottlenose dolphin performing a cross-modal matching-to-sample task was stationed on a biteplate while echolocating on a sample object concealed in an opaque box. This procedure prevented the animal from gaining different aspects of the stimulus. Despite these restrictions on his location the dolphin was still able to recognize the object and successfully perform a match. The echolocation signals emitted by the dolphin were recorded with a rectangular array of 16 hydrophones mounted on a frame and placed between the dolphin on the biteplate and the object inside the box. A custom high-frequency data acquisition system recorded the signals at 500 kS per second and also collected synchronized video from several locations around the animal. The collected data was filtered and processed. The results presented here show that the dolphin was scanning the object and steering his echolocation beam without moving his head thus avoiding the possible acoustic clutter from multiple reflections from the object. The ...

Is synthetic aperture an essential tool for echoic shape recognition in dolphins

A dolphin had previously been trained to perform a cross-modal matching-to-sample task. In one version of this task the animal had to investigate a sample object that was concealed in a box through its echolocation sense alone, then select the correct match among up to three alternative objects visually in air. Given the frequency range of a dolphin click and the limited number of sensors that the dolphin receives the sonar returns with, the dolphin should have difficulties resolving the details of the object. We suggested earlier that the dolphin might be using synthetic aperture to gain a higher resolution of the stimulus. To test this hypothesis we proposed to restrict the movement of the dolphin by stationing him on a bite-plate that was fixed in front of the box that contained the sample object. We trained the dolphin to station on the bite-plate while performing the cross-modal task (echolocation to vision) while recording the sound field around the dolphin through a 16-hydrophone array that was placed in a variety of positions and configurations between the object and the dolphin stationed on the bite-plate. The acoustic data were recorded at 500 kHz and later analyzed. To our surprise the dolphin was still able to perform the discrimination task. In this paper, we present the analysis of the data collected and show that the dolphin employs techniques such as beam steering and beam shaping while acoustically interrogating the object. This suggests that while the dolphin might still employ a synthetic aperture when possible, he might not need it to resolve the details of the object. We are planning to extend the range of objects to new and unfamiliar objects to explore whether the dolphin is indeed able to resolve details of the object acoustically without the need for synthetic aperture.