Lecture Notes on Bathymetry and Measurement Methods

Introduction

• Theme: The theme of the lecture involves bathymetry, focusing on historical and modern methods of measuring ocean depths.
• Historical Reference: Mention of Poseidon and early methods of measuring bathymetry, dating back to 85 BC.

Historical Methods of Measuring Bathymetry

• Soundings:
  • Originated with a simple method using a rope with a weight to measure depth.
  • Process: Rope is marked, lowered into the sea. Depth measured by tension release when weight hits the seafloor.
  • Complications: Currents affecting rope angle and length let out.

Significant Historical Efforts

• HMS Challenger Expedition (1872):
  • First systematic global bathymetric measurements using soundings.
  • Revealed variations in seafloor depth.
  • Expedition started with 216 people, ended with 144.

Modern Methods of Measuring Bathymetry

• Echo Sounder (Early 1900s):

  • Uses acoustic pings to determine seafloor depth.
  • Issues with integration and signal diffusion.
  • Led to discovery of the deep scattering layer.

• Multi-beam Echo Sounding:

  • Sends multiple wavelengths and angles of sound.
  • Provides better resolution maps of the seafloor.

• Side Scan Sonar:

  • Towed behind ships, providing detailed seafloor imagery.
  • Slow, but high detail compared to multi-beam.

Recent Developments

• Autonomous Underwater Vehicle (AUV):
  • Used for detailed mapping of seafloor features like hydrothermal vents.
  • Example: "Lucky's Mound", an inactive hydrothermal sulfide mound.

Satellite-Based Measurements

• Satellite Altimetry:
  • Measures gravitational influence of seafloor features on ocean surface.
  • Provides global seafloor maps with less detail compared to ship-based methods.
  • Example: TOPEX/Poseidon satellite.

Seismic Imaging

• Purpose: Used to understand sub-seafloor structures, important for oil exploration.
• Process: Uses air gun explosions for low-frequency sounds that penetrate seafloor layers.
• Data Interpretation: Shows faults and sediment layers, providing insights into tectonic activity.

Conclusion

• Next Topic: Future lectures will discuss different marine provinces and what can be found in them.
• Final Note: Encouragement to be respectful and kind.