GPL Detector Overview
Generalised Power Law Detector
Overview
The Generalised Power Law (GPL) Detector is a real time implementation of the detector described in Helble et al, 2012. This detector is particularly useful for the detection of highly variable tonal sounds, such as those from humpbacks, where correlation or other shape based detectors become ineffective.
A generalized power-law detection algorithm for humpback whale vocalizations. Tyler A. Helble, Glenn R. Ierley, Gerald L. D�Spain, and Marie A. Roch and John A. Hildebrand. The Journal of the Acoustical Society of America 131, 2682 (2012).
http://asa.scitation.org/doi/abs/10.1121/1.3685790
Algorithm
For details of the algorithm, see Helble et al 2012. The papers abstract is given here to give a quick summary of what happens. In many ways, the algorithm is similar to an in band energy detector, however by raising the amplitude of the data in a spectrogram to a higher power, tonal sounds become amplified by a much greater amount than broader band sources of noise such as shipping or wave motion.
ABSTRACT (from Helble et al, 2012)
Conventional detection of humpback vocalizations is often based on frequency summation of band-limited spectrograms under the assumption that energy (square of the Fourier amplitude) is the appropriate metric. Power-law detectors allow for a higher power of the Fourier amplitude, appropriate when the signal occupies a limited but unknown subset of these frequencies. Shipping noise is non-stationary and colored and problematic for many marine mammal detection algorithms. Modifications to the standard power-law form are introduced to minimize the effects of this noise. These same modifications also allow for a fixed detection threshold, applicable to broadly varying ocean acoustic environments. The detection algorithm is general enough to detect all types of humpback vocalizations. Tests presented in this paper show this algorithm matches human detection performance with an acceptably small probability of false alarms (PFA < 6%) for even the noisiest environments. The detector outperforms energy detection techniques, providing a probability of detection PD = 95% for PFA < 5% for three acoustic deployments, compared to PFA > 40% for two energy-based techniques. The generalized power-law detector also can be used for basic parameter estimation and can be adapted for other types of transient sounds.