Very satisfactory results have been obtained in estimating size abundances of small zooplankton such as copepods from inversion of multifrequency backscattering measurements. Application of this method has become almost routine in many situations. Fluctuations in the scatterer physical properties (density and compressibility) tend principally to cause errors in the abundance estimates whereas size estimates are largely unaffected. The model commonly employed for small crustacean scatterers, a truncated-mode version of the Anderson fluid sphere model, predicts bistatic scattering as well as monostatic backscattering. The behavior of bistatic scattering at angles approaching 90 deg predicted by this model shows that scattering spectra at these angles are quite sensitive to physical properties. This suggests that simultaneous measurements at multiple frequencies and one or more off-axis angles might permit estimation of the physical properties of zooplanktonic scatterers as well as their sizes. Preliminary modeling has been done for a single fluid scatterer to illustrate the potential for simultaneous estimation of size, density, and compressibility of zooplanktonic organisms in a laboratory setting. The character of the bistatic scattering may argue for nontraditional methods for inverting this sort of data.

The long-term goal of our research is to improve our ability to observe the ocean's plants, animals and their physical and chemical environment at critical scales that control how they live, reproduce and die. OBJECTIVES Our work is focused in two distinct, but related areas. The first addresses questions of the frequency of occurrence and characterization of thin layers in geographically separated, oceanographically diverse littoral environments. Our second research thrust involves continued development of measurement technology and models to support the use of multi-static, multi-frequency scattering in studies of small zooplankters and micronekton.

The long-term goal of our research is to improve our ability to observe the ocean's plants, animals and their physical and chemical environment at the critical scales which control how they live, reproduce and die.

The long-term goal of our research is to improve our ability to observe the ocean's plants, animals, and their physical and chemical environment at critical scales that control how they live, reproduce, and die. OBJECTIVESWe continue to work towards the development of new tools for studying zooplankton and micronekton in their natural habitat. Our current focus involves extending multi-frequency acoustics to include measurements at more than one angle with respect to the incident sound wave. APPROACHAlthough the use of multi-frequency backscattering methods has clearly improved our ability to study small zooplankton and micronekton in situ, the information one can extract from volume scattering and target strength measurements remains limited by the number of independent measurements one can

ONR Contract Number: N00014-98-C-0442http://206.251.232.34 LONG-TERM GOALSThe long-term goals of this research are to improve the ability of benthic biologists and biological oceanographers to observe life on and in the seabed; to describe the interactions between the animals that live there, their neighbors and their food; to improve our understanding of the coupling between the benthic and the pelagic communities; and to assess biologically mediated changes in those physical properties of the seabed that affect scattering and penetration of sound into the bottom. OBJECTIVESDirect observation of animals that live on or in the seabed can be exceptionally difficult. This is especially true in areas with characteristically poor visibility or in water that is too deep to allow divers to spend much time near the bottom. Little attention has been given to developing instrumentation and sensors that would allow remote observation of benthic animals for long periods at high spatial and temporal resolution. Our short-and medium-term objectives involve developing high frequency acoustic sensors to fill this gap, thereby improving the information that benthic ecologists can access about benthic and benthopelagic animals and the seabed environment. In addition, the presence and 1