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OBSERVATION OF AQUATIC animals in their natural environments remains a major challenge in both biological oceanography and limnology. Critical processes in feeding, reproduction, growth, and predation in small zooplankton occur at scales from fractions of millimeters up to scales that match the ambits of individuals. It is often difficult to reproduce all essential features of the marine environment in the lab, where observation of smallscale processes is more tractable than at sea. Therefore there is continuing interest in improving our ability to observe and quantify in situ spatial and temporal changes in the distribution and abundance of zooplankton in relation to natural physical, chemical, and other biological fields. Making accurate measurements of spatial distributions is difficult. Conventional CTD packages, fluorometers, and acoustical sensors, when used in a "cast" mode from a ship, tend to have-1 m vertical resolutions. The time it takes to make a measurement in relation to the "'drop" rate, the necessity to pump water through some kinds of sensors, the need to acquire and average multiple samples in a quasi-random, statistically nonstationary local environment, and the coupling of the motions of the ship to the sensor all contribute to "smearing" spatial pattern in the data. These practical issues tend to reduce the spatial resolution of measurements one obtains at sea. In many of our acoustical field studies of plankton, sea conditions and consequent uneven sampling in depth caused us, in