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2005
Munger, LM, Mellinger DK, Wiggins SM, Moore SE, Hildebrand JA.  2005.  Performance of spectrogram cross-correlation in detecting right whale calls in long-term recordings from the Bering Sea. Canadian Acoustics. 33:25-34. AbstractWebsite

We investigated the performance of spectrogram cross-correlation for automatically detecting North Pacific right whale (Eubalaena japonica) calls in long-term acoustic recordings from the southeastern Bering Sea. Data were sampled by autonomous, bottom-mounted hydrophones deployed in the southeastern Bering Sea from October 2000 through August 2002. A human analyst detected right whale calls within the first month (October 2000) of recorded data by visually examining spectrograms and by listening to recorded data; these manual detections were then compared to results of automated detection trials. Automated detection by spectrogram cross-correlation was implemented using a synthetic kernel based on the most common right whale call type. To optimize automated detection parameters, the analyst performed multiple trials on minutes-long and hour-long recordings and manually adjusted detection parameters between trials. A single set of optimized detection parameters was used to process a week-long recording from October 2000. The automated detector trials resulted in increasing proportions of false and missed detections with increasing data set duration, due to the higher proportion of acoustic noise and lower overall call rates in longer recordings. However, the automated detector missed only one calling "bout" (2 or more calls within a 10-minute span) of the 18 bouts present in the week-long recording. Despite the high number of false detections and missed individual calls, spectrogram cross-correlation was useful to guide a human analyst to sections of data with potential right whale calling bouts. Upon reviewing automatic detection events, the analyst could quickly dismiss false detections and search recordings before and after correct detections to find missed calls, thus improving the efficiency of searching for a small number of calls in long-term (months- to years-long) recordings.

2004
Wiggins, SM, McDonald MA, Munger LM, Moore SE, Hildebrand JA.  2004.  Waveguide propagation allows range estimates for North Pacific right whales in the Bering Sea. Canadian Acoustics. 32:146-154. AbstractWebsite

The shallow and uniform water depth of the eastern Bering Sea shelf results in an acoustic waveguide. Propagation within this waveguide produces waveform dispersion which is dependent upon range. We present a means for using dispersed waveforms to determine range to calling whales from a single autonomous acoustic recording instrument. The predominant North Pacific right whale (Evbalaena japonica) call is frequency upswept from about 90 Hz to around 160 Hz and lasts approximately 1 s. The regional bathymetry of the eastern Bering Sea middle shelf is relatively uniform and shallow ( similar to 70 meters deep). This geometry provides a plane-layered waveguide in which right whale upswept calls can be detected at ranges over 50 km and have multiple modal arrivals that become dispersed, displaying different propagation velocities for different frequencies. Dispersion characteristics of modal arrivals are dependent on the calling whale's depth, the receiver's depth, the water depth, the range from caller to receiver, and various environmental parameters including water and sediment density and sound velocity. A model of sound propagation for the eastern Bering Sea middle shelf is developed from right whale call dispersion recorded on sonobuoys and seafloor acoustic recording packages, using individual calls recorded at multiple instruments. After development of the model, waveform dispersion allows estimation of caller range based on single instrument recordings. Estimating range between instrument and calling whales provides a means to estimate minimum abundance for the endangered North Pacific right whale.Original Abstract: L'eau peu profonde et uniforme de la rive Est de la mer de Bering produit un excellent guide d'ondes acoustiques. Dans ce guide de propagation, la dispersion des ondes sonores est dependante de la distance. Nous presentons ici un moyen pour utiliser la dispersion des ondes sonores pour determiner la portee de sons emis par des baleines a partir d'un unique instrument d'enregistrement du signal acoustique. La vocalisation predominate de la baleine franche du Pacifique Nord (Eubalaena japonica) est une modulation ascendante d'environ 90 a 160 Hz et d'une duree approximative de 1 s. La bathymetrie regionale de la rive Est de la mer de Bering est relativement uniforme et peu profonde ( similar to 70 m de profondeur). Cette geometrie fournit un guide d'ondes a couches horizontales ou les vocalisations modulees de baleines tranches peuvent etre detectees a des distances superieures a 50 km et ont de multiples arrivees modales qui deviennent dispersees, demontrant differente vitesse de propagation a differentes frequences. Les caracteristiques de dispersion des arrivees modales sont dependantes de la profondeur de la baleine, la profondeur du recepteur, la profondeur de l'eau. la distance de l'emetteur et du recepteur et une variete de parametres environnementaux incluant la densite de l'eau et des sediments, et la vitesse du son dans ces deux media. Un modele de la propagation du son pour la rive Est de la mer de Bering est developpe a partir de la dispersion des vocalisations des baleines tranches enregistrees a partir de bouees acoustiques et de systemes acoustiques ancres sur le fond marin, en utilisant les vocalisations individuelles enregistrees a partir de multiples instruments. Apres le developpement du modele, la dispersion de l'onde sonore permet l'estimation de la distance de la vocalisation basee sur l'enregistrement d'un seul instrument. Estimer la distance entre l'instrument et les vocalisations de baleines permet d'estimer l'abondance minimale de la baleine franche menacee d'extinction dans le Pacitique Nord.