Analysis of Sperm Whale Click by MUSIC Algorithm

Inter-pulse interval (IPI) of the click projected from a sperm whale (phyeter macrocephalse) is expected to represent its size. IPI can be regarded as a distinguishing feature between individual sperm whales. Correlation analysis is used to measure IPI from recorded data. We analyzed data recorded off Ogasawara from 2003 to 2005 based on the correlation analysis. Although the results show its applicability for identification of individuals in data of 2003, it does not provide reasonable results for data recorded in 2004 and 2005, which include more noise comparing to those of 2003 when the noise in support vessel is not negligible. In this paper, we propose a new analysis method of sperm whale click based on MUSIC (multiple signal classification) algorithm in order to calculate IPI. MUSIC algorithm is the high-resolution frequency estimation method using orthogonality of signal and noise subspaces. It is said that it has high capacity for white noise. By estimating IPI from clicks data by proposed method and comparing to them to those by convention method, we examine applicability of MUSIC algorithm to classify individuals of sperm whale of analysis of data recorded in 2003. The result shows that proposed method can extract IPI in good conformity with those by convention method under the condition of low lever noise.