Marine Physical Laboratory Research Articles

Chester McKinney: Lessons I learned from a prominent scientist and leader in our acoustics community

The impression that was left with me from his speech after he received the ASA’s Gold Medal at the 1994 New York City meeting still remains indelible. It was exactly the way someone born in Cooper Texas, population 2,600 should communicate the excitement of his career journey to national and international leadership in science, academia, and the technology associated with national defense. Comfortable in front of a large audience, he walked back and forth on the stage with complete informality reminiscing about his experiences in the multiple worlds he inhabited. As the new director of Marine Physical Lab, SIO/UCSD one generation after his tenure as director of the Applied Research Labs, UT, he reaffirmed to me why he had served as my mentor by example. Here, I review some of the lessons that his career provided

A personal history of Doppler sonar development at the Marine Physical Laboratory, SIO

In the early 1970s, the possibility of remotely measuring oceanic and atmospheric flows was becoming appreciated. By then, techniques for information extraction from sets of discrete targets were well advanced. Inferring fluid motion from the echo off a random cloud of independent scatterers was a different issue, as illustrated by the abject failure of contemporary matched-filter technology. Conceptual as well as hardware challenges were addressed over time, leading to the variety of Doppler sonars and sodars available commercially today. In this talk, I focus on systems developed at the Marine Physical Laboratory of Scripps over the past 42 years. Both pulse-to-pulse coherent and incoherent backscatter systems are reviewed with an emphasis on real-world problems encountered. Presently, under-exploited techniques based on sea-surface scattering or bi-static geometries are discussed. While many quality Doppler sonar manufacturers are now active, a large gap exists between what is technically possible and what is commercially available. The continuing vitality of university-based development groups that create scientifically significant (but not necessarily commercially profitable) systems is critical to advancing the state of the art.

The University of California Division of War Research and the Marine Physical Laboratory

In 1941, motivated by the large-scale destruction of ships by submarines in World War II, three university-operated laboratories were established: Columbia University Division of War Research, Harvard Underwater Sound Laboratory, and The University of California Division of War Research (UCDWR). UCDWR was led initially by Vern Knudsen of the University of California, Los Angeles, with senior staff recruited from academic institutions across the country. After the war, UCDWR was dissolved with the The Navy Electronics Laboratory absorbing most of the UCDWR employees. Further, by agreement between the Navy and the Regents of the University of California, the Marine Physical Laboratory (MPL) was formed with an initial scientific staff of five people from UCDWR with Carl Eckart as its Director. We review this transition period and MPL’s subsequent trajectory within the University of California system to its ultimate venue in the Scripps Institution of Oceanography.

Propagation measurement using source tow and moored vertical line arrays during TREX13

The objective of TREX13 (Target and Reverberation EXperiment 2013) is to investigate shallow water reverberation by concurrently measuring propagation, local backscatter, and reverberation, as well as sufficient environmental parameters needed to achieve unambiguous model/data comparison. During TREX13 the Marine Physical Laboratory (MPL) conducted propagation and forward scatter measurements. The MPL effort during TREX13 included deploying three, 32-element (0.2 m element spacing), vertical line arrays along the Main Reverberation Track at a bearing of ~128° and ranges ~2.4 km, ~4.2 km, and ~0.5 km from the R/V Sharp, where reverberation measurements were being made. In addition, MPL carried out repeated source tows in the band of 2–9 kHz along the Main Reverberation Track, using tonal and LFM waveforms. The experimental procedure is described and the resulting source-tow data is examined in the context of Transmission Loss and its implications for reverberation.

Acoustical Oceanography and Underwater Acoustics Graduate Programs at the Scripps Institution of Oceanography of the University of California, San Diego

The Scripps Institution of Oceanography (SIO) of the University of California, San Diego (UCSD), has graduate programs in all areas of acoustics that intersect oceanography. These programs are associated mostly with internal SIO divisions that include the Marine Physical Laboratory, Physical Oceanography, Geophysics, and Biological Oceanography as well as SIO opportunities for other UCSD graduate students in the science and engineering departments. Course work includes basic wave physics, graduate mathematics, acoustics and signal processing, oceanography and biology, digital signal processing, and geophysics/seismology. Much of the emphasis at SIO includes at-sea experience. Recent examples of thesis research has been in marine mammal acoustics, ocean tomography and seismic/acoustic inversion methodology, acoustical signal processing, ocean ambient noise inversion, ocean/acoustic exploration, and acoustic sensing of the air-sea interaction. An overview of the SIO/UCSD graduate program is presented.

Day/night whole sky imagers for 24-h cloud and sky assessment: history and overview

A family of fully automated digital whole sky imagers (WSIs) has been developed at the Marine Physical Laboratory over many years, for a variety of research and military applications. The most advanced of these, the day/night whole sky imagers (D/N WSIs), acquire digital imagery of the full sky down to the horizon under all conditions from full sunlight to starlight. Cloud algorithms process the imagery to automatically detect the locations of cloud for both day and night. The instruments can provide absolute radiance distribution over the full radiance range from starlight through daylight. The WSIs were fielded in 1984, followed by the D/N WSIs in 1992. These many years of experience and development have resulted in very capable instruments and algorithms that remain unique. This article discusses the history of the development of the D/N WSIs, system design, algorithms, and data products. The paper cites many reports with more detailed technical documentation. Further details of calibration, day and night algorithms, and cloud free line-of-sight results will be discussed in future articles.

Intra-hour forecasting with a total sky imager at the UC San Diego solar energy testbed

Intra-hour forecasting with a total sky imager at the UC San Diego solar energy testbed Chi Wai Chow 1 , Bryan Urquhart 1 , Matthew Lave 1 , Anthony Dominguez 1 , Jan Kleissl 1 , Janet Shields 2 , Byron Washom 3 Department of Mechanical and Aerospace Engineering Marine Physical Laboratory, Scripps Institution of Oceanography Director, Strategic Energy Initiatives University of California, San Diego Phone: +1 858 534 8087 email: jkleissl@ucsd.edu Abstract A method for intra-hour, sub-kilometer cloud forecasting and irradiance nowcasting using a ground- based sky imager at the University of California, San Diego is presented. Sky images taken every 30 seconds were processed to determine sky cover using a clear sky library and sunshine parameter. From a two-dimensional cloud map generated from coordinate-transformed sky cover, cloud shadows at the surface were estimated. Limited validation on four partly cloudy days showed that (binary) cloud conditions were correctly nowcast 70% of the time for a network of six pyranometer ground stations spread out over an area of 2 km 2 . Cloud motion vectors were generated by cross-correlating two consecutive sky images. Cloud locations up to five minutes ahead were forecasted by advection of the two-dimensional cloud map. Cloud forecast error increased with increasing forecast horizon due to high cloud cover variability over the coastal site.

Honors

William Kuperman, professor of oceanography and director of the Marine Physical Laboratory of the Scripps Institution of Oceanography, University of California, San Diego, has been selected as the 2011 recipient of the Walter Munk Award for distinguished research in oceanography related to sound and the sea. The award, to be presented by the Oceanography Society this fall, recognizes significant original contributions to the understanding of physical ocean processes related to sound in the sea, among other factors. Laurie Leshin, deputy associate administrator of the Exploration Systems Mission Directorate (ESMD) at NASA Headquarters, is leaving the agency in September to become dean of the School of Science at Rensselaer Polytechnic Institute, Troy, N. Y. Leshin, who has served as ESMD deputy since 2010, joined NASA in 2005 as director of science and exploration at the Goddard Space Flight Center. She is president of the AGU Planetary Sciences section.

Technical Note: Determination of aerosol optical properties by a calibrated sky imager

Abstract. The calibrated ground-based sky imager developed in the Marine Physical Laboratory, the Whole Sky Imager (WSI), has been tested with data from the Atmospheric Radiation Measurement Program (ARM) at the Southern Great Plain site (SGP) to determine optical properties of the atmospheric aerosol. Different neural network-based models calculate the aerosol optical depth (AOD) for three wavelengths using the radiance extracted from the principal plane of sky images from the WSI as input parameters. The models use data from a CIMEL CE318 photometer for training and validation and the wavelengths used correspond to the closest wavelengths in both instruments. The spectral dependency of the AOD, characterized by the Ångström exponent α in the interval 440–870 nm, is also derived using the standard AERONET procedure and also with a neural network-based model using the values obtained with a CIMEL CE318. The deviations between the WSI derived AOD and the AOD retrieved by AERONET are within the nominal uncertainty assigned to the AERONET AOD calculation (±0.01), in 80% of the cases. The explanation of data variance by the model is over 92% in all cases. In the case of α, the deviation is within the uncertainty assigned to the AERONET α (±0.1) in 50% of the cases for the standard method and 84% for the neural network-based model. The explanation of data variance by the model is 63% for the standard method and 77% for the neural network-based model.

Measuring spike train reliability

Address: 1Institute for Nonlinear Sciences, University of California, San Diego, USA, 2Institute for Complex Systems, CNR, Sesto Fiorentino, Italy, 3Department of Information and Communication Technologies, Universitat Pompeu Fabra, Barcelona, Spain, 4Center for Brain Science, Harvard University, USA and 5Department of Physics and Marine Physical Laboratory (Scripps Institution of Oceanography), University of California, San Diego, USA

Temporal spike pattern learning

Sachin S. Talathi,* Henry D. I. Abarbanel, and William L. Ditto J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Florida 32611, USA Marine Physical Laboratory, Scripps Institution of Oceanography, Department of Physics and Center for Theoretical Biological Physics, University of California, San Diego, La Jolla, California 92093, USA Received 16 June 2008; revised manuscript received 11 August 2008; published 23 September 2008

Acoustic vector sensors and vector/tensor processing in ocean acoustics research

Several passive sensor systems that simultaneously measure acoustic pressure and the three components of acoustic particle motion have been designed and deployed in seagoing experiments by the Marine Physical Lab over the past two decades. Descriptions of these sensor systems and results from applying various signal/array processing methods with these data are presented in this talk. Although vector sensors do not provide any additional information on the sound field than that obtained by a suitable number of properly placed hydrophones, they do provide estimates of the sound field's directional properties from a very compact package. Applications where available space is severely limited include autonomous underwater vehicles (AUV). Recent results from acoustic vector sensors installed in a flying wing underwater glider and inside a prop-driven AUV to quietly measure sounds in the ocean illustrate the benefits, and drawbacks, of the use of vector sensors on autonomous platforms. The extension of the signal/array processing approaches to tensor sensors indicates the promise of additional gain, if the sensor design challenges can be overcome. [Work supported by the Office of Naval Research].

Acoustic sensor systems on a flying wing underwater glider and two prop‐driven autonomous underwater vehicles

The Marine Physical Laboratory, Scripps Institution of Oceanography operates several underwater vehicles including an autonomous underwater glider based on a flying wing design and two prop‐driven autonomous underwater vehicles (AUV) manufactured by Bluefin Robotics. The objective of this presentation is to describe the acoustic sensor systems on these platforms and provide sample results from the at‐sea data. The glider, with a 6.1‐m wing span, was developed jointly by the Marine Physical Lab and the Applied Physics Laboratory, University of Washington. It is designed to maximize the horizontal distance traveled between changes in buoyancy (i.e., maximize its "finesse") while quietly listening to sounds in the ocean. A 27‐element hydrophone array with 5 kHz per channel bandwidth is located in the sonar dome all along the wing's leading edge. In addition, it has a four‐component acoustic vector sensor in its nose. The two prop‐driven AUVs have been equipped with hull‐mounted hydrophone arrays with 10 kHz bandwidth for passive synthetic aperture studies, an acoustic vector sensor, and active acoustic imaging systems for ocean bottom/subbottom mapping. Results from the data processing illustrate the tight coupling between acoustic sensor systems, signal/array processing methods, and vehicle behavior. [Work supported by the Office of Naval Research.]

Ocean acoustic time reversal

A series of ocean acoustic time experiments have been jointly conducted in the last ten years by the NATO Undersea Research Centre and the Marine Physical Laboratory. The experiments demonstrated a robustness of the ocean acoustic time reversal mirror process similar to that found in more controlled, ultrasonic laboratory experiments. Results from these experiments have pointed to potential applications to SONAR signal processing methods and to acoustics communications. In addition, the experimental procedures themselves have yielded data that provide further understanding of the ocean acoustic environment and the increased stability of time reversal process over one way propagation in a fluctuating medium.

Underwater acoustic measurements with a flying wing glider

Liberdade, a new class of underwater glider based on a flying wing design, has been under development for the past 3 years in a joint project between the Marine Physical Laboratory, Scripps Institution of Oceanography and the Applied Physics Laboratory, University of Washington. This hydrodynamically efficient design maximizes the horizontal distance traveled between changes in buoyancy, thereby minimizing average power consumed in horizontal transport to achieve ‘‘persistence.’’ The first fully autonomous glider of this class, ‘‘XRay,’’ was deployed and operated successfully in the Monterey Bay 2006 experiment. Communications, including real-time glider status reports, were accomplished using an underwater acoustic modem as well as with an Iridium satellite system while on the surface. The payload included hydrophone array, with 10 kHz per channel bandwidth, located in a sonar dome along the leading edge of the 6.1-m-span wing. Narrowband tones from 3.0 to 8.5 kHz were transmitted from a ship-deployed controlled underwater source. During the glider’s flight, lift-to-drag ratios (equal to the inverse of the glide slope) exceeded 10/1. However, specific flight behaviors that deviated from this efficient horizontal transport mode allowed for improved detection and localization by the hydrophone array. [Work sponsored by the Office of Naval Research.]

Fred Noel Spiess

Fred Noel Spiess

Fred Fisher and research with acoustic vector sensors; Marine Physical Laboratory’s vertical array of directional acoustic receivers and ocean noise

Fred Fisher had boundless enthusiasm for all topics acoustic. A chance encounter with him in the hallway usually led to a half-hour discussion of the latest research efforts at the lab and recent results he found exciting. In the 1980s, Fred became interested in the problem of identifying the physical phenomena forming the pedestal about the horizontal in vertical directionality measurements of the deep ocean’s low-frequency noise field. Two competing mechanisms had been proposed: downslope conversion of coastal shipping and noise from high latitude winds coupling into the deep sound channel due to the shoaling of the sound channel axis. The relative contributions of these two mechanisms possibly could be separated if the azimuthal ambiguity of a vertical line array of hydrophones somehow could be broken. Therefore, Fred proposed to build a vertical array of ‘‘DIFAR’’ sensors, which led to the design and construction of the Marine Physical Lab’s Vertical ‘‘DIFAR’’ Array. This talk will reminisce a bit about Fred as well as present some results from an ambient noise experiment conducted in 1992 on the continental shelf using the Vertical DIFAR Array co-deployed with MPL’s freely drifting vector sensors, the Swallow floats. [Work supported by ONR and ONT.]

Underwater acoustic measurements with the Liberdade/X-Ray flying wing glider

An underwater glider based on a flying wing design (Jenkins et al., 2003) presently is under development by the Marine Physical Laboratory, Scripps Institution of Oceanography and the Applied Physics Laboratory, University of Washington. This design maximizes the horizontal distance between changes in buoyancy to minimize mechanical power consumed in horizontal transport. The prototype wing has a 6.1 m wing span and is 20 times larger by volume than existing gliders. Initial at-sea tests indicate that the lift-to-drag ratio is 17/1 at a horizontal speed of about 1.8 m/s for a 38-liter buoyancy engine. Beamforming results using recordings of the radiated noise from the deployment ship by two hydrophones mounted on the wing verify aspects of the prototype wing flight characteristics. The payload on the new glider will include a low-power, 32-element hydrophone array placed along the leading edge of the wing for large physical aperture at midfrequencies (above 1 kHz) and a 4-component vector sensor. Data previously collected by these types of arrays illustrate the performance of narrow-band detection and localization algorithms. Flight behaviors are being developed to maximize the arrays’ detection and localization capabilities. [Work sponsored by the Office of Naval Research.]

Decreasing the Radiated Acoustic and Vibration Noise of a Mid-Size AUV

An Odyssey IIb autonomous underwater vehicle (AUV) made by Bluefin Robotics, Inc., was acquired by the Marine Physical Laboratory, Scripps Institution of Oceanography, to conduct research in underwater acoustics as well as provide a platform for other scientific studies. The original Odyssey IIb tail cone was replaced with a ducted fan, vectored thrust system installed on vehicles currently sold by Bluefin. In initial sea tests with the new thrust system, the acoustic self noise levels of the vehicle while underway were 20 to 50 dB higher than typical ocean background noise levels, preventing the vehicle's use as a receiver of low level sounds. Controlled tests were performed to characterize the radiated and vibration noise of the AUV propulsion and actuators. Once this baseline was established, changes were made, mostly to the tail cone propulsion, to decrease the vehicle's self noise. The resulting self noise levels of the AUV from 10 Hz up to 10 kHz measured while underway by a hydrophone mounted on the AUV's inner shroud now are at or below typical shallow water background noise levels except in three bands; below 250 Hz, around 500 Hz, and from 0.9 to 2.0 kHz. The goal of this paper is to describe these changes and their effects in lowering vehicle noise levels.

Diurnal variability in the anisotropic nature of the ocean’s midfrequency (1–10 kHz) noise field

A 131‐element, 2‐D billboard array with 12‐kHz bandwidth per element and interelement spacing equal to half‐wavelength at 3.75 kHz was designed and built by the Marine Physical Lab. It recorded data nearly continuously over 8 days in July, 2002. The site was in 175‐m water located 2 km from the ‘‘43‐Fathom Spot,’’ a popular fishing area in the Southern California Bight. Results from combined conventional beamforming in the vertical and adaptive beamforming in the horizontal commonly display a strong azimuthal dependence of the vertical directionality. A noise notch in the horizontal typically exists at many azimuths during daytime hours, sometimes more than 15 dB lower than higher‐angle energy. Numerical modeling illustrates the importance of local (within 20‐km range) large‐scale bathymetry variations. However, at night, the horizontal noise levels can exceed those at higher angles by more than 10 dB. Horizontal beam spectrograms show two broad peaks centered at 1.5 kHz and around 4.5 kHz that appear shortly after sunset, are strongest at midnight, and disappear at sunrise. This horizontal energy arrives from the direction of the 43‐Fathom Spot and probably represents a nighttime chorusing behavior of some species of fish or invertebrate. [Work supported by ONR, Code 321(US).]