Fluctuations I: spatial and temporal scales of importance for low-frequency propagation

Over the past 5 to 10 years much of the work in fluctuations has been broadly exploratory, intended to characterize observable time and space scales of fluctuation and to identify the environmental phenomena responsible. Much of Project MIMI (Miami/Michigan), with both fixed-system and moving-source experiments, has been devoted to this task. Although the data base now established is useful in providing direction for future work that is more application-oriented, more survey data of this type are needed, particularly at very low acoustic frequencies. More information is required, for example, on the space and time scale of fluctuations which degrade performance in array reception and which influence phase coherence at multisite receivers. A better definition is needed also of the relative importance of temporal and spatial variability in the medium for fluctuations in signals from moving sources. This paper presents data and discussion pertinent to these needs.