Measuring underwater noise levels

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Measuring underwater noise levels
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Measuring the underwater noise level

• Step 1 Calibrating the hydrophone
• 250 Hz, 157 dB re 1 µPa continuous tone from a
  calibrator
• Measure the voltage produced by known pressure
  using an oscilloscope (V1 552 mV 157 dB 20 dB
  137 dB re 1 µPa )

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Measuring the underwater noise level

• Step2 Measuring system noise
• Hydrophone acoustically (almost) isolated
• Voltage produced by the whole system involved
  measured for each 1/3 octave band.

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Measuring the underwater noise level

• Step 3 Measurements underwater
• Hydrophone lowered to a depth of 2m
• Sound level (RMS) in mV measured from the
  oscilloscope for each 1/3 octave BW.

!!!
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Measuring the underwater noise level

• Step 4 Calculations
• Example

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Noise measurements for Group II
130,0
120,0
110,0
100,0
90,0
SYSTEM
dB re 1uPa2/Hz
80,0
UNDERWATER
70,0
60,0
50,0
40,0
30,0
1
10
100
1000
10000
100000
1E06
Center frequency
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Noise measurements for Group I
130,0
120,0
110,0
100,0
90,0
SYSTEM
dB re 1uPa2/Hz
80,0
UNDERWATER
70,0
60,0
50,0
40,0
30,0
1
10
100
1000
10000
10000
0
Center frequency
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