How Can I Effectively Calibrate A Cabled Ocean Bottom Seismometer To Accurately Detect And Quantify The Low-frequency Sounds Emitted By A Migrating Humpback Whale Population In The Presence Of Ambient Noise From Nearby Shipping Lanes And Coastal Development?

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To effectively calibrate a cabled ocean bottom seismometer for detecting and quantifying low-frequency sounds from migrating humpback whales amidst ambient noise, follow this organized approach:

1. Calibration Process

  • Use a Known Sound Source: Employ a specialized underwater sound source (e.g., calibration piston) emitting known frequencies and amplitudes. Place it near the seismometer to record responses.
  • Determine Transfer Function: Calculate the transfer function by comparing the seismometer's output voltage to the input pressure. This involves synchronizing sound emission with data recording.
  • Adjust Sensitivity: Use the transfer function to adjust the sensor's sensitivity, ensuring accurate conversion of seismic data to sound pressure.

2. Noise Mitigation

  • Band-Pass Filtering: Apply a filter tuned to humpback whale vocalization frequencies (10 Hz to 500 Hz) to reduce ambient noise.
  • Machine Learning/Pattern Recognition: Train models to identify whale call patterns, enhancing detection amidst noise.

3. Data Acquisition Settings

  • Sampling Rate: Set a minimum of 1000 Hz to capture up to 500 Hz frequencies, adhering to the Nyquist theorem.
  • Dynamic Range Management: Adjust gain settings to handle varying sound amplitudes without distortion.

4. Environmental Considerations

  • Sound Velocity Profile: Account for water depth, temperature, and salinity to adjust calibration as needed.
  • Orientation and Deployment: Ensure correct positioning of the seismometer to optimize signal capture.

5. Data Processing

  • Power Spectral Density (PSD) Analysis: Compare noise and signal PSDs to assess signal-to-noise ratio.
  • Filtering Techniques: Apply notch filters for specific noise frequencies and detiding to remove tidal effects.

6. Field Testing and Validation

  • Field Deployment: Validate the setup in the field by comparing data with known whale signals.
  • Iterative Adjustment: Make necessary adjustments based on field results.

7. Equipment and Documentation

  • Seismometer Type: Confirm if it's a geophone or hydrophone and apply appropriate calibration methods.
  • Documentation: Thoroughly record calibration parameters, environmental conditions, and adjustments for reproducibility.

8. Further Research and Collaboration

  • Literature Review: Consult existing research on calibrating seismometers for bioacoustic applications.
  • Expert Consultation: Engage with experts for specialized insights and troubleshooting.

By systematically addressing each component, you can optimize the seismometer's performance to accurately detect and quantify whale sounds in a noisy environment.