Optimizing transmit interval and logging range while avoiding aliased seabed echoes

Abstract

Abstract Echosounder surveys of fish and zooplankton are typically conducted using fixed values of the echosounder transmit-pulse (“ping”) interval and data-logging range. The transmit-pulse interval must be long enough to sample to the range of the farthest (deepest) species under study, potentially causing undersampling of closer (shallower) species. We present an algorithm to dynamically minimize both the logging range and transmit-pulse interval while ensuring that the logging range equals or exceeds the range to the seabed up to a chosen maximum data-logging range. The algorithm also allows avoidance of aliased seabed echoes (“false bottoms”) by adjusting the minimized transmit interval such that seabed reverberation from a previous transmission is not present in the data logged for an ensuing transmission. Additionally, periodic measures of ambient noise allow evaluations of signal quality and useful range. This optimization scheme (“adaptive logging”) effectively increases the horizontal resolution and signal-to-noise ratio of the data, and may reduce the total data volume and storage-space requirement. The efficacy of the adaptive logging algorithm is quantified using simulations. Furthermore, an example implementation of the algorithm is demonstrated for a commonly used scientific echosounder (Simrad EK60).