🔍 Day 23: Integrating Side Scan Sonar (SSS) with MBES
🖼️ DAY 23: SIDE SCAN SONAR INTEGRATION
Masterpiece Edition – Towfish, Real‑Time Imagery, Target Detection & Georeferencing
Instructor: Engr. Rokib Hossain | River Warrior Academy
📖 Table of Contents (Serialised)
- What is Side Scan Sonar?
- Towfish vs Hull‑Mounted
- Integrating Side Scan with MBES / GNSS
- Real‑Time Display & Target Marking
- Field Workflow Diagram
- Complete Integration Checklist
- Essential External Resources (Authority Domains)
- Frequently Asked Questions (with internal links)
- Action Items & Next Steps
- Post‑Verification Checklist (SEO & Engineering)
1. What is Side Scan Sonar?
Side scan sonar produces acoustic images of the seabed by emitting fan‑shaped pulses to port and starboard. It is essential for detecting wrecks, pipelines, cables, and seabed texture. Unlike MBES, it does not give bathymetry but provides extremely high‑resolution imagery (centimetre level).
Side scan sonar coverage – two swaths producing seabed imagery.
2. Towfish vs Hull‑Mounted
Two main deployment methods:
- Towfish: Depressor wing and cable. Can be deployed from small boats. Depth capability up to 100‑200 m. Requires careful cable length management.
- Hull‑mounted (fixed): Installed in a pod or through‑hull. Better for high‑speed surveys (up to 10 knots). More expensive, requires professional installation.
🧠 Expert Note – Layback Calculation: The horizontal offset between vessel GNSS antenna and towfish = cable length × sin(depression angle). For accurate georeferencing, measure layback and enter into acquisition software.
3. Integrating Side Scan with MBES / GNSS
For georeferenced side scan mosaics, you need:
- GNSS position of the towfish (or vessel) with layback correction.
- Heading and motion sensor to correct towfish yaw and roll.
- Synchronisation with MBES – most acquisition software can record side scan alongside MBES (e.g., Hypack Side Scan module, QINSy Sidescan).
1️⃣ Measure layback (distance from GNSS antenna to tow point)
2️⃣ Enter cable out length and offset in software
3️⃣ Set ping rate to avoid interference with MBES
4️⃣ Record raw side scan files (.xtf, .s7k, .sss)
📌 Layback formula: Towfish position = Vessel position + (cable length × sin(depth angle)) in direction of vessel heading.
4. Real‑Time Display & Target Marking
Modern acquisition software displays side scan waterfall in real time. Hydrographer can mark targets (wrecks, pipelines) directly on the screen. Key QC:
- Gain settings – avoid over/under saturation.
- Range – adjust to cover full swath (e.g., 50 m per side).
- Contrast – enhance target visibility.
- Track lines – ensure 100% coverage with 20% overlap.
Real‑time side scan waterfall – targets appear as dark/light shadows.
5. Field Workflow Diagram
6. Complete Integration Checklist
- ✅ Pre‑deployment: Inspect towfish connector, cable for cuts. Test in test tank.
- ✅ Vessel setup: Measure layback distance from GNSS antenna to tow point.
- ✅ Software config: Enter layback, cable out length, sensor offsets.
- ✅ During survey: Adjust gain/range to maintain consistent image quality. Keep speed 3‑5 knots.
- ✅ Target marking: Record time, line number, and approximate size.
- ✅ End of day: Export raw side scan files, back up to external drive.
8. Frequently Asked Questions (with internal links)
🔹 Can I run side scan simultaneously with MBES?
Yes, most acquisition software supports both. Ensure ping rates do not interfere – typically side scan uses lower frequency (100‑400 kHz) and MBES uses higher (200‑400 kHz). Some systems use frequency filtering. Review Day 7: SBES vs MBES.
🔹 What is the optimal towfish depth?
Typically 10‑15% of water depth (e.g., at 30 m depth, towfish at 3‑5 m above seabed). Too low = risk of hitting seabed; too high = reduced resolution. See Day 10: Survey Planning for line planning.
🔹 How to avoid side scan noise from propeller?
Towfish must be deployed at least 3‑5 times the vessel length behind the stern. Also use a vibration dampener on the cable. Day 12: Transducer Mounting covers mechanical alignment.
🔹 What is the difference between .xtf and .sss format?
.xtf (Extensible Transducer Format) is the industry standard for side scan data. .sss is a simpler format used by some systems. Always log in .xtf for compatibility. Day 20: Data Logging explains file management.
🔹 How do I georeference side scan if I don’t have a USBL?
Use layback correction based on vessel GNSS and heading. For deeper water (>50 m), a USBL (Ultra‑Short Baseline) is recommended. Day 22: GNSS & Tide covers positioning accuracy.
9. Action Items & Next Steps
- 📌 Download a sample .xtf file and open it in a free viewer (e.g., SonarWiz Map).
- 📌 Calculate layback for a towfish with 50 m cable, water depth 30 m, and cable angle 20°.
- 📌 Write a short SOP for “Daily side scan start‑up checks”.
- 📌 Proceed to Day 24: Troubleshooting Data Acquisition.
10. Post‑Verification Checklist (For Each Post)
✅ SEO & Rich Results Verification
- □ Canonical URL matches the post URL.
- □ datePublished and dateModified are current (2026-05-15).
- □ Schema markup passes Google Rich Results Test.
- □ Open Graph and Twitter Card are present.
✅ Content & Internal Linking Verification
- □ Table of Contents uses numbered list with working anchors.
- □ All internal links (Day 7, Day 10, Day 12, Day 20, Day 22, Day 24 placeholder) work.
- □ External links open in new tab.
- □ Print button and black box function correctly.
✅ Technical & Mobile Verification
- □ Tables have `overflow-x: auto` wrapper – no horizontal break on 375px.
- □ SVG diagrams scale without overflow.
- □ No JavaScript errors in console.
🔗 Internal linking complete: Day 22 is linked. When Day 24 is published, replace the placeholder.
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