Acoustic Technology -- Introduction

Introduction

Background

What is GLOBEC?

GLOBEC (GLOBal Ocean ECosystems Dynamics) is a science component of the U.S. Global Change Research Program. Planning efforts for the U.S. component of the GLOBEC research initiative are sponsored by NSF with NOAA and ONR participation. The GLOBEC concept involves gaining an understanding of how physical processes, both direct and indirect, influence the success of individual animals in the sea through their feeding, reproduction, and survivorship. GLOBEC also addresses relationships between the success of the individual and the dynamics of the population. Additional information on GLOBEC can be obtained by requesting the U.S. GLOBEC Report Series from JOI, Inc. (1755 Massachusetts Avenue, NW, Suite 800, Washington, DC 20036-2102). A list of the reports that are currently available are included in the References.

Steering Committee Function and Objectives

The U.S. GLOBEC Steering Committee was established to plan, promote, and coordinate the physical sciences-biological sciences partnership needed to assess the consequences of changing global climate on marine animal production. The current membership of the Steering Committee is provided in Appendix A. One goal of the Steering Committee is to provide an assessment of the current and future availability of appropriate technology to groups planning the science components of GLOBEC. Specifically, there is a need to describe the research, development, organization, and resources needed to make advanced technology available to assist the community in reaching GLOBEC's science goals. It is also timely to provide the interested funding agencies with the science and technology community's view of the potential, cost, and time required to develop or acquire candidate instrumentation and technology in support of the GLOBEC effort.

The Role of New Measurement Technology

The Steering Committee for the U.S component of GLOBEC is attempting to anticipate and describe the necessary technological tools and advances for support of the GLOBEC research initiative during the 1990's.

It is anticipated that substantial progress will arise from the development and application of new technologies for sampling of both the biota and the physical environment. Additional advancements are expected from the interactive collaboration of physical oceanographers, technologists, and biological oceanographers, as well as from the stimulation and opportunities that the GLOBEC initiative provides to investigators in the ocean sciences community. One of the keys to advancing our understanding of the relationship between ocean physics and the distributions of animals in the sea is the rapid, simultaneous measurement of each. Given the potential gains in understanding ocean ecosystem dynamics through application of new technology, it is evident that timely development of necessary sampling technology and measurement tools is of critical importance to GLOBEC.

Underwater acoustics and underwater optics appear to be appropriate tools for quantitative assessment of fish and zooplankton. Additionally, simultaneous and complementary uses of acoustical and optical technology may bring advantages to both disciplines. In support of the GLOBEC science planning activities, a Workshop on Acoustical Technology and the Integration of Acoustical and Optical Sampling Methods was held in Woods Hole, Massachusetts on April 2-4, 1991. The Woods Hole Oceanographic Institution and the NOAA National Marine Fisheries Service, Northeast Fisheries Center were hosts for the meeting. This report attempts to document the key findings of the workshop participants.

Objectives of the Workshop

Fisheries acoustics is relatively advanced compared to the state of the development of acoustic technology for studying micronekton and macrozooplankton. The use of acoustics for studying small zooplankton is also relatively new and the joint use of acoustics and optics is an unexplored area. It was recognized that, since the different working groups were dealing with disciplines which varied in their maturity, not all of the issues would be appropriate for each group. Consequently, the order and priority in which issues were addressed was left to each group.

The following issues and challenges were identified as being of interest to the GLOBEC Steering Committee.

The issues of priority, protocol, cost, and time frame for instrument acquisition and technology development need to be addressed in 3 categories: 1) off-the-shelf instrumentation; 2) modification or adaptation of off-the-shelf gear at moderate cost; and 3) critical new research or development focuses for instrumentation or methodology.
Development of a protocol for instrument calibration to ensure valid comparisons of measurement results among different geographic areas, times, projects, and investigators.
Protocols within which unique or complex instruments can be accessed by investigators within the GLOBEC community, and definition of a route to the development and construction of an infrastructure for GLOBEC that will assure and support such access.
The role of acoustical and optical technology in quantifying and linking different scales of measurement in time and space for GLOBEC.
As appropriate for each working group, recommendations for "calls for proposals" in specific areas of acoustical and acoustical/optical technology which should be considered by the GLOBEC Steering Committee and possibly to be forwarded by that group to appropriate funding agencies.
Any other areas in acoustics, optics, and the integration of those two disciplines that the working groups might deem critical or important in preparing the science and technology communities to address GLOBEC science issues.

As one examines the individual working group reports, it will be evident that some issues were considered to have a higher priority than others. Some issues were addressed in detail and others were only discussed briefly or not at all. It should be noted that the time constraint of a little more than one day for working group meetings precluded addressing all issues in equal detail.

Workshop Organization

To achieve an adequate representation of the technical disciplines needed to address GLOBEC's acoustical and optical technology requirements meant bringing together biological oceanographers, fisheries scientists, physical oceanographers, mathematical modelers, physicists, electrical engineers, and a variety of other technical specialties (see Appendix B for list of workshop participants). A small, informal poll of the invitees, before the workshop convened, revealed that individual participants knew a third or fewer of the other workshop attendees. The success of such interdisciplinary meetings is often the clear definition of the common problem to be addressed. To provide a common starting base, one-half of the first day was dedicated to definition of GLOBEC and a description of the science problems and environments of interest to potential GLOBEC investigators. The second half of the first day included several presentations that reviewed the history and the state-of-the-art in the acoustical and optical technologies on which GLOBEC technologists will likely draw in developing instrumentation and methodology. In recognition of the diverse backgrounds of the workshop participants, the speakers attempted to emphasize concepts, general methods, and results rather than technical detail.

On the morning of the first day a description of the developing GLOBEC science focus and of several GLOBEC field programs under discussion for the 1990's was presented (see Appendix C- Meeting Agenda). These presentations provided examples of the science issues related to GLOBEC that would benefit from the application of existing, modified, and/or new acoustic technology as it impacts our ability to understand the dynamics of typical ocean ecosystems. They also provided an indication of the range of ocean environments that may be encountered in GLOBEC studies. The ocean environment is often a limiting factor in the performance of acoustic and optical instrumentation.

The afternoon of the first day was dedicated to review and survey papers by investigators who are active in four related research areas: 1) fisheries acoustics; 2) mesopelagic fish acoustics; 3) euphausiid (krill) acoustics; and 4) zooplankton acoustics.

On the second day, several working groups were convened. Three of these strived to identify applicable acoustic instrumentation and technologies in historically distinct, but overlapping bioacoustic disciplines of: fisheries acoustics, micronekton/macro-zooplankton acoustics, and small zooplankton acoustics. A fourth working group focused on the possible integration of acoustical and optical techniques. The groups were asked to address the following: the availability of off-the-shelf instrumentation; existing instrumentation that could be modified quickly and at moderate cost; existing technology that is not yet widely available, but could be made so in the time-frame of GLOBEC; and new concepts that could have a major impact on the science in the 1990's if the necessary resources were made available for research and development.

Applicable technology and methods as well as instruments were identified. In areas where a consensus evolved from the deliberations, general priorities for funding of instrument acquisition as well as research and development were recommended. Ways to increase the availability of necessary instrumentation to all GLOBEC investigators were also solicited. For example, in some cases, acquisition of low cost instruments by individual investigators, or small groups, within the context of their science proposals may be most appropriate. In other cases, the acquisition of unique or high-cost instruments or facilities by larger coalitions of scientists interested in providing a service to the community may be the most practical approach. Following brief meetings of the working groups, a panel discussion of mechanisms for developing educational and training opportunities for undergraduates, graduate students, and postdoctoral scientists opened the plenary session on the third morning. The workshop concluded at noon with presentations by the working group chairmen summarizing the findings of each group. The Editorial Committee (see inside cover) then turned its attention to the integration of the separate working group reports into a compatible format.

Working groups were organized within traditional acoustic subject divisions rather than those possibly more common to the biological disciplines. The acoustical method of grouping the organisms that live in the sea is largely based on size, numbers/m³, and to some degree, their behavior, environment, and distribution. These are all important parameters in determining the acoustic methods and operating parameters to be used for detecting and quantifying distribution, abundance, and characteristics of the animals. Both the acoustical and the biological method of grouping subjects is somewhat artificial. There is often overlap in the types of acoustic technology used to examine the range of sizes between egg and adult life stages, and interactions between trophic levels in the food web. Likewise, the complexity of the marine food web makes it difficult to examine any individual species or group in total isolation.

The fisheries acoustics group dealt principally with adult nekton. The micronekton/macroplankton group included scientists with interests in juvenile and larval fishes, myctophids, euphausiids, and large zooplankton. In general, these animals are complex scatterers of sound, requiring application of either very simple (e.g., empirical regression models) or reasonably complex mathematical formulations (e.g., rough, bent cylinder scattering models) to describe their acoustic reflectivities. While improvements in scattering models applicable to small zooplankton will probably be a natural outcome of continued work on those organisms, variations on the fluid sphere model have been used with some success since 1950 (Anderson, 1950) to describe the acoustic reflectivity of small crustaceans such as copepods. The original division of the micronekton/macroplankton group and the small zooplankton group was based on the type of scattering model that might be most appropriate to describe the scattering from the target organisms. Subsequently, the working group dealing with small zooplankton decided that, in view of the range of capabilities of the technologies under discussion in the group, they should also consider organisms at least as large as the smaller euphausiids. The group charged with examining the potential for integrating acoustical and optical sampling technologies dealt with all sizes and genera for which those techniques appeared to be appropriate.