Echo Sounder Bathymetry: How Sound Maps the Seafloor

From Ping to Profile

An echo sounder (fathometer) measures depth by timing sound's round-trip to the bottom.

Step-by-Step Process

1. Transmit: Transducer emits acoustic pulse (12–200 kHz; lower = deeper penetration)
2. Travel: Sound moves through water at ~1,500 m/s (varies with T, S, P)
3. Reflect: Pulse hits seafloor; echoes return
4. Receive: Transducer detects return; timer stops
5. Calculate: Depth = (speed × time) / 2
6. Log/Display: Continuous profile along ship track

System Types

• Single-beam: One vertical cone; 1D profile
• Multibeam (MBES): Fan of beams (100+); 2D swath (100–200% depth width)
• Side-scan sonar: Near-horizontal; high-res imagery, not precise depth
• Sub-bottom profiler: Low frequency; images sediment layers below seafloor

Corrections Applied

• Sound velocity profiles (CTD casts or MVP)
• Tide/water level (to chart datum)
• Vessel motion (heave, pitch, roll – via IMU)
• Transducer draft (offset)

Output

Bathymetric grids (GeoTIFF, XYZ), contour charts, 3D models, habitat maps. Foundation for navigation, habitat science, resource exploration, cable/pipeline routing, climate studies.