applications of cross correlation
DESCRIPTION
ADSP (cross corellation)TRANSCRIPT
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Applications of cross correlation
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Cross correlation• In signal processing, cross-correlation is a measure of similarity of
two waveforms as a function of a time-lag applied to one of them. This is also known as a sliding dot product or sliding inner-product.
• For continuous functions, f and g, the cross-correlation is defined as:
• where f* denotes the complex conjugate of f.• Similarly, for discrete functions, the cross-correlation is defined as:
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Applications of cross correlation
• pattern recognition• Signal detector• Weather forecasting• Security system designing• Water traffic monitoring
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Cross-correlation of ship noise for water traffic monitoring
•One of the vessel features that can be remotely measured and used for vessel detectionand classification is the vessel's acoustic signature
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Water traffic monitoring
• Any moving vessel radiates an underwater sound whose parameters depend on the vessel hull structure, machinery , propeller, etc.
• Measurements of underwater sound radiated by vessels can provide enough information for vessel identification.
• Underwater sounds can be listen by using the hydrophones.
• A hydrophone is a microphone designed to be used in underwater for recording or listening the underwater sound.
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Water traffic monitoring
•We considered a method that enables such tasks as vessel tracking and individual vessel signature extraction in busy environments, using a system with a few hydrophones. This method is based on cross-correlation processing of acoustic signals detected by different hydrophones.
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Water traffic monitoring
• The noise radiated by a ship propagates underwater and reaches the hydrophones at different times due to different propagation distances.
• This delay depends on the direction of the ship.
• The core of the cross-correlation method is based on the analysis of the timedelays in the recorded signals.
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Water traffic monitoring•An example of the calculated cross-correlation between twohydrophones for two vessels :
•The time variation of the cross-correlation function can be presented in the form of afloating chart similar to a spectrogram. Such graph has two geometric dimensions: thehorizontal axis represents time, the vertical axis is the delay between two hydrophonesignals; a third dimension is shown in color indicating the amplitude of a cross correlation function.
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Water traffic monitoring
• We used the cross-correlation function for calculating the spectral density of the vessels’ sound.
• The spectral density of the received signal is directly related to the spectral density of their cross-correlation.
• While contributions of different boats cannot be separated in the time domain, they can be separated in delay in the cross-correlation: the spectrum of the contribution of a vessel in the cross-correlation gives an estimation of the spectra of sound radiated from this vessel.
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Water traffic monitoring
• But the problem is that, this method is not suitable for busy areas like big harbours and estuary etc….
• Only the developed cross-correlation method allows vessel’s detection and tracking in busy estuary and harbor environments.
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