📡 DAY 7: SBES vs MBES – SINGLE BEAM vs MULTIBEAM

Choosing the Right Sonar for Your Hydrographic Survey

Instructor: Engr. Rokib Hossain | River Engineering Solutions

📖 Today's Outline

🔊 Introduction to Echo Sounders
📡 Single Beam Echo Sounder (SBES) – Principles & Limitations
🌊 Multibeam Echo Sounder (MBES) – Swath Bathymetry
⚖️ Head‑to‑Head Comparison: SBES vs MBES
🗺️ When to Use Which – Practical Scenarios
🔧 Modern MBES Features (FM Chirp, Dual Swath, Multi‑Ping)
🔗 External Resources & Manufacturers
📋 Homework & Fieldwork Checklists
❓ Frequently Asked Questions
✅ Action Items & Internal Linking

🔊 Introduction to Echo Sounders

Echo sounders are the primary tools for measuring water depth. They work by transmitting an acoustic pulse and measuring the two‑way travel time. The basic formula:

Depth = (c × t) / 2

Where c = sound velocity (m/s) and t = two‑way travel time (seconds).

Two main types dominate hydrography: Single Beam Echo Sounder (SBES) and Multibeam Echo Sounder (MBES). Each has distinct advantages, costs, and applications.

📌 Key concept: SBES gives one depth per ping. MBES gives hundreds of depths (a swath) per ping, covering the seafloor like a "lawnmower".

📡 Single Beam Echo Sounder (SBES) – Principles & Limitations

How it works: A single transducer (often 200 kHz or 33 kHz) emits a narrow beam (typically 5°–12°). It measures the depth directly under the vessel. To create a bathymetric map, the vessel must sail along parallel lines, and depths are recorded at regular intervals (e.g., every 1‑10 m).

Advantages:

✅ Low cost – hardware and software are relatively inexpensive.
✅ Simple to operate and maintain.
✅ Suitable for shallow, small‑area surveys where full coverage is not required.
✅ Lower power consumption, easy to deploy on small boats.

Limitations:

❌ Provides only a single point per ping – gaps between lines may miss features.
❌ Low spatial resolution – cannot resolve small targets or complex seabed.
❌ Inefficient for large areas – requires many line kilometres.
❌ No true 100% bottom coverage unless lines are extremely dense.

🎯 [Diagram: SBES footprint – narrow beam, single depth point per ping]
(Replace with your own image)

🌊 Multibeam Echo Sounder (MBES) – Swath Bathymetry

How it works: An MBES uses a transducer array to form multiple beams (often 256 to 1024) that fan out across the vessel's track. The swath width is typically 3–6 times the water depth. For each ping, the system records hundreds of depths, providing 100% bottom coverage along the survey line.

Advantages:

✅ High resolution – captures detailed seabed features, wrecks, pipelines.
✅ High efficiency – covers large areas quickly, reducing survey time.
✅ True 100% bottom coverage (when swath overlaps correctly).
✅ Simultaneous bathymetry and backscatter (acoustic imagery).

Limitations:

❌ Expensive – hardware, software, and training cost much higher.
❌ Complex installation and calibration (patch test, IMU alignment).
❌ Requires accurate motion sensing (heave, pitch, roll) and heading.
❌ More sensitive to sound velocity errors – ray‑bending corrections are critical.

🌊 [Diagram: MBES swath – fan of beams covering wide area]
(Replace with your own image)

⚖️ Head‑to‑Head Comparison: SBES vs MBES

Feature	Single Beam (SBES)	Multibeam (MBES)
Coverage per ping	1 depth point	100–1000 depth points
Swath width	~beam footprint (narrow)	3–6 × water depth
Bottom coverage	Not 100% (gap between lines)	100% (if line spacing correct)
Resolution	Low – misses small features	High – can detect 1 m objects
Ideal depth range	All depths, but inefficient in deep	Shallow to full ocean depth
Typical applications	Dredging (crude), fishing, reconnaissance	Port surveys, cables, wrecks, high‑accuracy charts
Cost (approx.)	$3k – $30k	$100k – $500k+
Motion correction	Optional (heave only)	Essential (heave, pitch, roll, yaw)

📊 Productivity example: In 20 m water, a MBES with 120° swath covers ~70 m per line. SBES would need 70× more line kilometres to achieve the same point density.

🗺️ When to Use Which – Practical Scenarios

Choose SBES when:

🔹 Budget is very limited and only rough depth data is needed.
🔹 Survey area is small and shallow (e.g., a single pier foundation).
🔹 You only need depths along a specific track (e.g., river cross‑sections).
🔹 As a backup or emergency system on a vessel.

Choose MBES when:

🔹 High resolution and 100% coverage are required (port surveys, cable/pipeline routes).
🔹 You need to detect small objects (wrecks, boulders, unexploded ordnance).
🔹 Survey area is large (e.g., offshore wind farm site).
🔹 You also need backscatter strength for seabed classification.

Many hydrographic offices now mandate MBES for all new nautical charting surveys because of its superior coverage and quality.

🔧 Modern MBES Features (FM Chirp, Dual Swath, Multi‑Ping)

Today's MBES systems include advanced capabilities:

Frequency Modulated (FM) Chirp – improves range resolution and signal‑to‑noise ratio.
Dual swath / Multi‑swath – interleaved pings to increase coverage or resolution.
Multi‑ping – transmit several pings before the first returns arrive, increasing ping rate.
Water column imaging – visualises fish, gas seeps, and mid‑water targets.
Integrated INS (Inertial Navigation System) – provides real‑time, accurate motion and heading.

Popular MBES manufacturers: Kongsberg (EM series), Teledyne RESON (SeaBat T series), R2Sonic (Sonic 2026), Norbit (iWBMS).

🔗 External Resources & Manufacturers

Explore these links for detailed specifications, white papers, and training materials:

Resource	Description	Link
Kongsberg Maritime MBES	EM series – industry standard for deep & shallow water	kongsberg.com
Teledyne RESON SeaBat	High‑resolution shallow‑water MBES	teledyne-reson.com
R2Sonic	Flexible frequency MBES for coastal surveys	r2sonic.com
NOAA MBES Training	Free online resources on multibeam principles	ngdc.noaa.gov

🔗 Authority linking: Links to manufacturers and NOAA increase credibility.

📋 Homework & Fieldwork Checklists

📘 Day 7 – Homework Checklist

✅ Read the entire Day 7 post.
✅ Visit the website of at least one MBES manufacturer (e.g., Kongsberg) and note the maximum swath coverage in a specific depth (e.g., 50 m).
✅ Calculate: If you have a 500 m × 500 m area, and you use an SBES with 10 m line spacing, how many line kilometres are needed? Compare with an MBES that covers 60 m per line.
✅ Write a paragraph: "Why is MBES mandatory for modern nautical charting?"
✅ Share this post with #Hydrography #SBESvsMBES.

🛠️ Fieldwork Readiness Checklist – Sonar Selection

✅ Before quoting a project, confirm the required coverage (e.g., IHO Order 1a requires 100% bottom coverage).
✅ If using SBES, design line spacing to meet the required feature detection (e.g., 2× beam footprint).
✅ For MBES, plan line spacing to achieve at least 20% overlap between adjacent swaths.
✅ Verify that the vessel can mount the MBES transducer with minimal interference (hull, propeller noise).
✅ Schedule a patch test (calibration) for MBES before production survey.
✅ Ensure motion sensor (IMU) is properly aligned and interfaced.

🖨️ Pro tip: Use the Print / Download PDF button to keep these checklists in your field binder.

❓ Frequently Asked Questions

🔹 Can a single beam echosounder also produce a bathymetric chart? ▼

Yes, but the chart will have low resolution and may miss features between survey lines. For IHO‑compliant charts, MBES is generally required for areas where full bottom coverage is mandatory.

🔹 How deep can a typical MBES work? ▼

Shallow‑water MBES (e.g., 200‑400 kHz) works from 0.5 m to ~200 m. Deep‑water MBES (12‑30 kHz) can reach full ocean depth (>11,000 m).

🔹 What is the patch test? ▼

A patch test is a series of calibration lines (roll, pitch, yaw, latency) performed to determine the precise alignment offsets between the MBES transducer, the motion sensor, and the GNSS. It is essential for accurate MBES data.

🔹 Is SBES obsolete? ▼

Not completely. SBES is still used for simple dredge volume calculations, fishing echo sounding, and as a backup. But for professional hydrographic surveys, MBES (or interferometric sonar) is the standard.

🔹 Can I mount MBES on a small boat? ▼

Yes. Many compact MBES systems (e.g., Norbit iWBMS, Sonic 2024) are designed for small vessels. However, you still need proper mounting (no bubbles) and a motion sensor.

✅ Action Items & Internal Linking

🎯 Your Tasks for Today

📌 Step 1: Bookmark the Course Homepage and at least two MBES manufacturer pages.
📌 Step 2: Download the checklist PDF using the button at the top.
📌 Step 3: Watch a YouTube video about MBES patch test to visualise the process.
📌 Step 4: Leave a comment on this post: "The typical depth range for my local harbour is ____, so I would use ____ sonar."
📌 Step 5: Proceed to Day 8: GNSS RTK vs PPK – Deep Dive using the link below.

🔗 Internal linking note: Day 6 and Day 8 are correctly linked. This builds a strong internal network for SEO.

🛰️ Day 7: SBES vs. MBES – The Fundamental Differences

SBES vs MBES – Single Beam vs Multibeam