Distributed vibration measuring device and method

A method of measuring dynamic strain of a sensing fiber, the method comprising:

• repeatedly supplying frequency swept lights to the sensing fiber;
• receiving backscattered light from the sensing fiber;
• combining local light, the local light being a part of a frequency swept light of the frequency swept lights, with the backscattered light to generate a beat signal;
• executing Fourier transform on the beat signal to obtain a backscattered light waveform;
• executing Fourier transform in a freely selected spectrum analysis section of the backscattered light waveform to obtain an optical spectrum;
• and
• obtaining, based on the amount of spectrum shift between a spectrum obtained in reference measurement and a spectrum obtained from the backscattered light for one sweep of the frequency swept lights, a strain amount of the dynamic strain in a section of the sensing fiber corresponding to the spectrum analysis section,
• wherein a length of the spectrum analysis section is set to be larger than a distance deviation amount Nd of the spectrum analysis section caused by frequency modulation due to the dynamic strain.

A device configured to measure dynamic strain, the device comprising:

• an optical circuit unit configured to repeatedly supply frequency swept lights to a sensing fiber,
• receive backscattered light from the sensing fiber, and
• combine local light, the local light being a part of a frequency swept light of the frequency swept lights, with the backscattered light;
• and
• an optical reception and analysis unit configured to generate a beat signal from the local light and the backscattered light,
• obtain a backscattered light waveform from the beat signal,
• obtain an optical spectrum in a freely selected spectrum analysis section of the backscattered light waveform, and
• obtain a strain amount of the dynamic strain in a section of the sensing fiber corresponding to the spectrum analysis section,
• wherein a length N of the spectrum analysis section is set with respect to an assumed distance deviation amount Nd caused by the dynamic strain such that a probability of a correlation peak exceeding a noise level has a desired value when correlation measurement between a spectrum of reference measurement and the optical spectrum is performed, the desired value being approximate to 1.

A method of measuring dynamic strain, the method comprising:

• repeatedly supplying frequency swept lights to a sensing fiber;
• receiving backscattered light from the sensing fiber;
• combining local light, the local light being a part of a frequency swept light of the frequency swept lights, with the backscattered light to generate a beat signal;
• obtaining a backscattered light waveform from the beat signal;
• obtaining an optical spectrum in a freely selected spectrum analysis section of the backscattered light waveform;
• and
• obtaining a strain amount of the dynamic strain in a section of the sensing fiber corresponding to the spectrum analysis section,
• wherein a length N of the spectrum analysis section is set with respect to an assumed distance deviation amount Nd caused by the dynamic strain such that a probability of a correlation peak exceeding a noise level has a desired value when correlation measurement between a spectrum of reference measurement and the optical spectrum is performed, the desired value being approximate to 1.