Browsing by Author "Versfeld, D. J. J"
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Item An empirical mode decomposition based hidden Markov model approach for detection of Bryde’s whale pulse calls(The journal of the Acoustical Society of America, 2020-02-11) Ogundile, O. O.; Usman, A. M.; Versfeld, D. J. JThis letter proposes an empirical mode decomposition (EMD) based hidden Markov model (HMM) approach for the detection of mysticetes’ pulse calls such as the Bryde’s whales. The HMM detection capabilities depend on the deployed feature extraction (FE) technique. The EMD is proposed as a performance efficient alternative to the popular Mel-scale frequency cepstral coefficient (MFCC) and linear predictive coefficient (LPC) FE techniques. The amplitude modulation–frequency modulation components derived from the EMD process are modified to form feature vectors for the HMM. Also, the ensemble EMD (EEMD) is adapted in a similar way as the EMD. These proposed EMD-HMM and EEMD-HMM approaches achieved better performance in comparison to the MFCC-HMM and LPC-HMMapproaches.Item A hidden Markov model with selective time domain feature extraction to detect inshore Bryde's whale short pulse calls(Elsevier, 2020-04-02) Ogundile, O. O.; Usman, A. M.; Versfeld, D. J. JAn Increase in the study of cetaceans' sounds has motivated the development of different automated sound detection and classification techniques. Passive acoustic monitoring (PAM) is extensively used to study these cetaceans' sounds over a period to understand their daily activities within their ecosystem. Using PAM, the gathered sound datasets are usually large and impractical to manually analyse and detect. Thus, hidden Markov models (HMM) is one of the popular tools used to automatically detect and classify these cetaceans' sounds. Nonetheless, HMM rely heavily on the employed feature extraction method such as Mel-scale frequency cepstral coefficients (MFCC) and linear predictive coding (LPC). In most cases, the more reliable the extracted feature vector from the known sound label, the higher the sensitivity of the HMM. Although these aforementioned feature extraction methods are widely used, their design is based on filters and requires windowing, fast Fourier transforms (FFT), and logarithm operations. Consequently, this increases the computational time complexity of the HMM. Here, we describe a selective time domain feature extraction method that can be easily adapted with the HMM. This proposed feature extraction method uses a combination of some simple but robust parameters such as the mean, relative amplitude and relative power/energy (MAP), which are selected based on empirical observations of the call to be detected. The performance of this proposed MAP-HMM was verified using the acoustic dataset of continuous recordings of an inshore Bryde's whale (Balaenoptera) short pulse calls collected in a single site in False bay, South-West of South Africa. Aside from exhibiting a low computational complexity, the proposed MAP-HMM offers superior sensitivity and false discovery rate performances in comparison to the LPCHMM and MFCC-HMM.Item Review of Automatic Detection and Classification Techniques for Cetacean Vocalization(Institute of Electrical and Electronics Engineers (IEEE)., 2020-06-08) Usman, A. M; Ogundile, O. O; Versfeld, D. J. JCetaceans have elicited the attention of researchers in recent decades due to their importance to the ecosystem and their economic values. They use sound for communication, echolocation and other social activities. Their sounds are highly non-stationary, transitory and range from short to long sounds. Passive acoustic monitoring (PAM) is a popular method used for monitoring cetaceans in their ecosystems. The volumes of data accumulated using PAM are usually big, so they are difficult to analyze using manual inspection. Therefore different techniques with mixed outcomes have been developed for the automatic detection and classification of signals of different cetacean species. So far, no single technique developed is perfect to detect and classify the vocalizations of over 82 known species due to variability in time-frequency, difference in the amplitude among species and within species' vocal repertoire, physical environment, among others. The accuracy of any detector or classifier depends on the technique adopted as well as the nature of the signal to be analyzed. In this article, we review the existing techniques for the automatic detection and classification of cetacean vocalizations. We categorize the surveyed techniques, while emphasizing the advantages and disadvantages of these techniques. The article suggests possible research directions that can improve existing detection and classification techniques. In addition, the article recommends other suitable techniques that can be used to analyze non-linear and non-stationary signals such as the cetaceans' signals. Several research have been dedicated to this topic, however, there is no review of these past results that gives a quick overview in the area of cetacean detection and classification. This review will help researchers and practitioners in the field to make insightful decisions based on their requirements.