Abstract
The analysis and classification of the sounds produced by certain animal species, notably anurans, have revealed these amphibians to be a potentially strong indicator of temperature fluctuations and therefore of the existence of climate change. Environmental monitoring systems using Wireless Sensor Networks are therefore of interest to obtain indicators of global warming. For the automatic classification of the sounds recorded on such systems, the proper representation of the sound spectrum is essential since it contains the information required for cataloguing anuran calls. The present paper focuses on this process of feature extraction by exploring three alternatives: the standardized MPEG-7, the Filter Bank Energy (FBE), and the Mel Frequency Cepstral Coefficients (MFCC). Moreover, various values for every option in the extraction of spectrum features have been considered. Throughout the paper, it is shown that representing the frame spectrum with pure FBE offers slightly worse results than using the MPEG-7 features. This performance can easily be increased, however, by rescaling the FBE in a double dimension: vertically, by taking the logarithm of the energies; and, horizontally, by applying mel scaling in the filter banks. On the other hand, representing the spectrum in the cepstral domain, as in MFCC, has shown additional marginal improvements in classification performance.
Highlights
One of the well-known consequences of climate change is its impact on the development of basic physiological functions of various species [3,4,5,6,7], such as the sound produced in the mating call, which plays a central role in sexual selection and reproduction of numerous ectothermic species
The main aim of this paper is to explore the feature extraction process, that is, to analyse the best way to represent the information contained in a sound frame
We present the results obtained in a set of experiments conducted to obtain the optimal representation of the anuran call spectrum in order to provide a more efficient classification
Summary
Environmental Monitoring of Anuran Calls as Indicators of Climate Change. The intended purpose is seldom related to the direct measurement of a parameter, and requires the analysis of complex phenomena. An example of this approach is phenology, which deals with the study of periodic plant and animal life cycles, and how some events are related to seasonal and climate variations [1] and, to global warming. A further example is provided by environmental monitoring operations, such as the use of the wildfire acoustic emission spectrum as the indicator of the type of forest fire [2]. One of the well-known consequences of climate change is its impact on the development of basic physiological functions of various species [3,4,5,6,7], such as the sound produced in the mating call, which plays a central role in sexual selection and reproduction of numerous ectothermic species
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