Estimating distances to baleen whales using multipath arrivals recorded by individual seafloor seismometers at full ocean depth.

This article focuses on developing and evaluating single-station multipath ranging methods to estimate horizontal ranges to singing fin whales and, in one case, sei whales at full ocean depths using ocean bottom seismometers (OBSs). The study tested two approaches—summed spectrogram stacking and autocorrelation of detection scores—across five deep-water OBS sites with varying seafloor properties, bathymetry, and sediment layers in the North Pacific and Atlantic Oceans. Results indicate that the autocorrelation method is more robust for detecting low-amplitude multipath arrivals and estimating ranges up to over 15 km, though challenges arise from bathymetric relief, subsurface reflections, closely spaced calls, and chorusing by multiple whales. The study highlights the importance of site-specific modeling of seafloor and subsurface properties and suggests combining multipath ranging with particle motion methods and independent cue rate data to improve baleen whale population density estimates from passive acoustic monitoring.