Noise reduction method and apparatus

A noise reduction method for reducing noise which overlaps detected signals in a high frequency band and is generated from sources different from a signal source during detection of distributed signals generated from the signal source at a plurality of measurement points comprising the steps of:

• computing system parameters for a plurality of detected signals, the system parameters corresponding to a plurality of coefficients wherein a detected signal measured at an arbitrary measurement point can be expressed as a linear combination of the system parameters and all other detected signals using the least squares method, with M samples of signals derived from the detected signals, where M+1 is equal to or larger than the number of said plurality of measurement points;
• extracting low frequency components from the detected signal with a zero-phase low-pass filter to obtain a basic signal which is free from noise;
• subtracting said basic signal from the detected signal to obtain a residual signal which comprises signal components of an original signal and overlapping noise;
• generating a comparison signal corresponding to said residual signal detected from said arbitrary measurement point by weighting said residual signals of said all other measurement points with the computed system parameters and summing all the weighted residual signals,
• computing a noise index which reflects the level of noise contained in said detected signal by calculating the coherence of said residual signal and said comparison signal of the corresponding measurement point;
• removing said overlapping noise contained in said residual signal to obtain said signal components in said residual signal by multiplying said residual signal by multiplying said residual signal with said noise index;
• and
• restoring the original signal as an output by adding said signal components contained in said residual signal to said basic signal.

A noise reduction apparatus for reducing noise which overlaps detected signals and is generated from sources different from a signal source during detection of distributed signals generated from the signal source at a plurality of measurement points comprising:

• basic signal detecting means for detecting a basic signal which is free from noise;
• subtracting means for subtracting said basic signal from said detected signal to obtain a residual signal which comprises signal components of an original signal and overlapping noise;
• parameter computing means for computing system parameters for a plurality of detected signals, the system parameters corresponding to a plurality of coefficients wherein a detected signal measured at said arbitrary measurement point can be expressed as a linear combination of the system parameters and all other detected signals using the least squares method with M samples of signals where M+1 is equal to or larger than the number of said plurality of measurement points;
• comparison signal generating means for generating a comparison signal corresponding to said residual signal detected from said arbitrary measurement point by weighting said residual signals of said all other measurement points with the computed system parameters, and summing all the weighted residual signals,
• noise index computing means for computing a noise index which reflects the level of noise contained in the detected signal by calculating the coherence of said residual signal and said comparison signal of the corresponding measurement point;
• noise removing means for removing said overlapping noise contained in said residual signal to obtain said signal components in said residual signal by multiplying said residual signal with said noise index;
• and adding means for restoring the original signal as an output by adding said signal components contained in said residual signal to said basic signal.

A noise reduction apparatus for reducing noise which overlaps detected signals in a high frequency band and is generated from sources different from a signal source during detection of distributed signals generated from the signal source at a plurality of measurement points comprising:

• basic signal detecting means for detecting low frequency components to obtain a basic signal which is free from noise;
• subtracting means for subtracting said basic signal from said detected signal to obtain a residual signal which comprises signal components of an original signal and the overlapping noise;
• parameter computing means for computing system parameters for a plurality of detected signals, the system parameters corresponding to a plurality of coefficients wherein a detected signal measured at said arbitrary, measurement point can be expressed as a linear combination of the system parameters and all other detected signals using the least squares method with M samples of signals where M+1 is equal to or larger than the number of said plurality of measurement points;
• comparison signal generating means for generating a comparison signal corresponding to said residual signal detected from said arbitrary measurement point by weighting said residual signals of said all other measurement points with computed system parameters, and summing all the weighted residual signals,
• noise index computing means for computing a noise index which reflects the level of noise contained in the detected signal by calculating the coherence of said residual signal and said comparison signal for the corresponding measurement point;
• noise removing means for removing said overlapping noise contained in said residual signal to obtain said signal components in said residual signal by multiplying said residual signal with said noise index;
• and
• adding means for restoring the original signal as an output by adding said signal components contained in said residual signal to said basic signal.