Flood-fill algorithms used for passive acoustic detection and tracking

Flood-fill algorithms are used in the ldquobucketrdquo tool of paint programs to fill connected parts of a bitmap with color. They establish the area connected to a given node in a multi-dimensional array. This paper outlines the implementation a recursive flood-fill algorithm. Two elements are defined as connected if a path exists between them along which the value of all elements exceeds some threshold for a given node and threshold. The flood-fill is performed recursively on all elements connected to the node of interest. Two applications for passive acoustic monitoring are explored: (1) Signal detection via two-dimensional (frequency and time) flood-fill applied to spectrograms; (2) Source tracking via four-dimensional (x, y, z, and time) flood-fill applied to source position likelihood volumes (obtained using a localization algorithm that gives the likelihood of a source occupying a point in time and space).