Khosrow Lashkari

Sound production of gray whales, Eschrichtius robustus, along their migration route: A new approach to signal analysis

Sound production of gray whales was investigated to determine their acoustic repertoire along the migration route, and to compare sound production in deep and shallow water. Recording was conducted off Monterey Bay and Carmel Bay, California, during the annual migrations of 1988 through 1991. Sounds were analyzed through digital signal processing. Six acoustic variables were measured. Three variables were used for final classification, chosen for their clarity in the presence of high levels of ambient noise (poor signal-to-noise ratio). These variables were 3-dB bandwidth, center frequency, and harmonic/sideband interval. Q ratio was used as an indicator of how broadband or narrow band a signal was relative to other gray whale signals. Four categories of signals were determined: M1, M3, M4, and M5. All signal types were concentrated below 1500 Hz. M3 signals had the lowest center frequency, averaging below 100 Hz. M1 were pulses and bonging signals, M3 were low-frequency moans, M4 were grunts, and M5 were subsurface exhalations. The rate of sound production was lower when whales traveled over deep water than over shallow water. Rate of sound production was less along the migration route compared to the lagoons. M3 signals were the most common, comprising 46.6% of the repertoire along the migration route, with M1 signals comprising 37.4%.

Vertical array receptions of the Heard Island transmissions

A long, vertical line array was deployed off Monterey, California during the Heard Island Feasibility Test to measure the modal content of the received signals. The array contained 32, equally spaced hydrophones spanning from 345 to 1740‐m depth. The multichannel data were recorded through a tether to the R/V Point Sur. The measurements had very low signal to noise ratios and indicated the cw transmission losses were approximately 140 dB for a source/receiver range of 17 000 km. Modal content was analyzed using (i) the modal extent versus depth, (ii) frequency‐vertical wave‐number spectra, (iii) modal beamforming and (iv) least squares fitting. All led to the conclusion that the modal population is surprisingly rich. There was strong evidence of population up to at least mode seven in the data.

Vertical array resolution of the normal modes from the Heard Island signals.

A 32‐element, 1.3‐km vertical array was deployed off Monterey, CA from the R/V Point Sur during the signal transmission from Heard Island. The signals were received with an SNR on a single channel of approximately −10 dB re:1 Hz. Narrow‐band filtering to 15 mHz improves this to +5 dB. The suspension system was designed to minimize array motion and array tilt and depth were monitored at two locations in the array. The multichannel data have been decomposed into normal modes using a time varying least‐squares representation. Initial processing of the data indicates the first four modes can represent 75% of the energy of the average projection over a 180‐s window. The time‐varying structure of the representation and the effect of array tilt and Doppler spread will also be discussed. [Work supported by Dept. of Energy, Monterey Bay Aquarium Res. Inst. and the Commander, Naval Postgraduate School.]

A feasibility field study of monitoring blue whales using the Pt. Sur Ocean Acoustic Observatory

In the summer of 1997, two three‐day experiments were conducted to test the feasibility of acoustically detecting, classifying, localizing, and tracking blue whales at long ranges using a former SOSUS listening array located at the Naval Postgraduate School Ocean Acoustic Observatory (OAO) at Pt. Sur, California. During each experiment, full‐array data were archived continuously at the OAO. In concert with the shore‐based acoustic monitoring, an aircraft was assigned to locate blue whales in the Monterey Bay National Marine Sanctuary and to direct a research vessel to a whale site. The research vessel was manned with observers and instrumented with a towed hydrophone array to ground‐truth the locations of the blue whales and classify the vocalized near‐field signals. These shipboard measurements were required to provide a means to separate the source signal characteristics from the multipath signatures for the calibration and validation of broadband, model‐based localization methods. In this presentation,...

Monterey Bay acoustic environmental monitoring system.

Over the past few decades sound has been used with increasing success to measure and monitor a variety of oceanographic features and processes−biological populations, water structure, internal waves, bathymetry, and climatic change to name just a few. Monterey Bay and surrounding ocean regions have recently been proposed as a Marine Sanctuary. Scientists see this region as a natural marine laboratory. In an effort to unobtrusively monitor features and processes in this ocean region a group of local scientists have initiated the design of an Acoustic Environmental Monitoring System (AEMS). A preliminary design meeting was held 28–29 February 1992 by a group of interested scientists and engineers at the Monterey Bay Aquarium. This paper reports on the preliminary design and objectives of the AEMS based on that meeting. The AEMS will consist of three monitoring sites within Monterey Bay, one near the head of Monterey Canyon, and two on the adjacent shelf areas. The sites will be connected to shore by high ba...

A new technique for joint optimization of excitation and model parameters in parametric speech coders

In a speech coding system, synthesis error (the difference between the original speech at the encoder input and the reproduced speech at the decoder output) is a more relevant measure of signal distortion than linear prediction (LP) error. By minimizing the synthesis error instead of the linear prediction error, the analysis and synthesis stages become more compatible. While LP error is linear in filter parameters, synthesis error is a highly nonlinear function of these parameters, making it computationally intractable for real‐time applications. This paper presents a computationally feasible solution for minimizing the synthesis error applicable for joint optimization of the excitation and model parameters in real time. Using a gradient search in the root domain, synthesis error is minimized by re‐optimizing the filter parameters for a given excitation. Starting the gradient search from the LPC solution, the resultant synthesis error produced by the proposed technique is guaranteed to be lower than the s...

Complete optimization of excitation and model parameters in parametric speech coders

In a speech coding system, synthesis error (the difference between the original speech at the encoder input and reproduced speech at the decoder output) is a more relevant measure of signal distortion than linear prediction (LP) error. By minimizing the synthesis error instead of the linear prediction error, the analysis and synthesis stages become more compatible. In a previous paper (J. Acoust. Soc. Am. 109, 2491), an Analysis‐by‐Synthesis (AbS) technique for joint optimization of the excitation and filter parameters in parametric speech coders were presented. Using a gradient search in the root domain, synthesis error is minimized by reoptimizing the filter parameters for a given excitation. This paper provides a major improvement over the previous work, resulting in more than 3 dB of gain in the segmental signal‐to‐noise ratio. The improvement is due to a new algorithm for computing the gradient vector in the gradient search procedure. The paper describes the new algorithm and report on the improved r...

Passive acoustic tracking of echolocating harbor porpoise (Phocoena phocoena). I. Fisheries management requirements and biological basis

Harbor porpoises are incidentally taken in various sink gillnet fisheries nationally. Little is known about the mechanism of these entanglements. To protect these animals as required by the Marine Mammal Protection Act (MMPA), fishery managers use time area closures and/or permit the use of acoustic deterrent devices (pingers) to reduce bycatch. To understand how an entanglement occurs and how the pingers function, one must understand the underwater behavior of the animals. Studies of captive porpoises, and using mounted instrumentation on released animals, have shown some aspects of porpoise life history but may or may not reveal natural behavior. A research program was initiated to determine the feasibility of passively tracking wild harbor porpoise using their echolocation signals (clicks) and observing their underwater movements in three dimensions. Additionally, details of these movements during feeding, traveling, and social events may provide an insight into their behavior that makes them prone to ...

Passive acoustic tracking of echolocating harbor porpoises (Phocoena phocoena). II. Methodology and results

Harbor porpoises (Phocoena phocoena) generate ultrasonic echolocation signals in the 110–150 kHz frequency range and social calls below 20 kHz. The high‐frequency ‘‘clicks’’ can be used to acoustically localize and track these animals in three dimensions at ranges within 500 m. In addition, the lower‐frequency social calls may be used for longer‐range localization. This presentation describes the techniques and methods for passively tracking harbor porpoises using these echolocation clicks and social calls. The approach is based on a time‐difference‐of‐arrival (TDOA) direction finding and line‐of‐position (LOP) fixing from two arrays spaced 60‐m apart. Each bottom‐mounted array consists of four hydrophones in a 1‐m tetrahedral configuration cabled 300 m to shore. Porpoise signal characteristics such as frequency, bandwidth, pulse rate, source level, and beamwidth and their effects on tracking are reviewed. Various components of the tracking system such as the hydrophone array, signal‐conditioning electron...

Temporal and spatial distribution of whale calls off Monterey, California

Twenty‐seven hours of acoustic data were recorded from a horizontal array in deep waters off the central coast of California. These data were analyzed to determine the characteristics of diverse underwater acoustic sources. Some of the identified sources were: moored RAFOS sources at ranges of 150–1000 km, low‐frequency ship and machinery noise, and sounds of biological origin. Over 400 whale calls were identified and analyzed to determine the distribution of these calls in both time and azimuth. Spectral analysis of the vocalizations indicate that most of the calls were from humpback whales. [Work supported by the United States Navy, Naval Postgraduate School, and Monterey Bay Aquarium Research Institute.]