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Part Ten - Signal-To-Noise Ratio Improvement Techniques - I. Summary; Survey Of Electromagnetic And Seismic Noise Related To Mine Rescue Communications - Volume II
  • Published Date:
    1/1/1974
Filetype[PDF - 688.10 KB]


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    During the detection phase, several procedures can be used to improve the signal-to-noise ratio (SIN) . • Subarrays of up to 10 seismometers should be used. The apparent failure to obtain improvement in SIN in the Westinghouse subarrav work is probably due to excessive noise in the electronics. The spacings needed for sensors in the subarray must still be established. • The sensors should be buried. Even burial to a few feet will probably give appreciable reduction of noise. A deeper burial will probably further reduce the noise; and, if the seismometers can be put below the weathered layer, the signal level will probably be increased. The reduction in noise by burial will be especially effective during high noise periods due to wind or rain. • Before attempting detection, the waveforms should be bandpass filtered. The bandpass should go from 25 Hz to an upper frequency of 100 to 200 Hz. Further measurements with a low noise system must be done before the signal-to-noise ratio can be determined for the 100 to 200 Hz range. Any narrow band noise should be removed by notch filters. • If noise levels differ among seismometers of a subarray, weights inversely proportional to the noise power should be applied to the seismometers. • Automatic methods of screening data for possible signal arrivals should be developed, but the final determination that the signal on a subarray output appears to be from a miner should be made by an analyst. Detection of "signal" on several subarrays should be required for positive identification. In the location phase, after detection: • If repeated signals are received, they should be coherently added (stacked) to give as good a SIN as possible for use in determining signal arrival times, to be used in location computations. The miner should, if possible, repeat the signal 25 to 50 times.

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