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 scales that 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 the critical scales which control how they live, reproduce and die.

Our long-term interests involve the possibility that biogenic activity can influence acoustic scattering at the water column-seabed interface and the propagation of sound in and over a sandy substrate in a shallow-water coastal marine environment. Evidence from laboratory studies on sand collected from the surf zone clearly demonstrates that gas bubbles can be formed when photosynthesis by benthic microalgae causes pore water to become supersaturated with oxygen. OBJECTIVES The next logical step is to determine whether this phenomenon occurs in the coastal ocean. The nearterm objective of the work is to determine whether photosynthesis produces conditions that lead to the formation of oxygen bubbles in the top few millimeters of shallow sandy coastal sediments, and if it does, how such bubbles change the acoustic reflectivity of the seabed.