What is a multibeam patch test?

A multibeam patch test is a calibration procedure to determine the angular offsets (pitch, roll, heading) and latency between the sonar head, motion sensor, and GNSS antenna. It ensures accurate depth and positioning for hydrographic surveys.

How often should I perform a patch test?

A patch test should be performed at the start of every survey project, after any equipment change (e.g., transducer mount, motion sensor, GNSS antenna), and whenever you suspect calibration drift.

What is the acceptable tolerance for patch test offsets?

Typical acceptable residuals are: Pitch < 0.05°, Roll < 0.05°, Heading < 0.1°, and Latency < 5 ms. These ensure IHO S-44 Special Order compliance.

Multibeam Echosounder Calibration (Patch Test) – Step-by-Step Guide + Interactive Simulator

📡 Multibeam Echosounder Calibration (Patch Test)

Master pitch, roll, heading, and latency offsets – 3D interactive simulator + field checklist

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A properly calibrated multibeam echosounder (MBES) is essential for high‑accuracy hydrographic surveys. Patch tests determine the angular misalignments between the sonar head, motion sensor, and GNSS antenna. This interactive guide walks you through each step with a real‑time 3D visualizer.

🎯 Why Calibration Matters

Pitch offset → depth errors (affects dredging volumes)
Roll offset → across‑track seabed slope errors
Heading offset → layback and positioning errors
Latency → along‑track mismatches (worst in fast survey speeds)

🛠️ Interactive Patch Test Simulator

Adjust each parameter below. The 3D visualization shows how misalignments affect the swath geometry. Green = well‑calibrated, Red = error visible.

Pitch Offset (°): 0.00

Roll Offset (°): 0.00

Heading Offset (°): 0.00

Latency (ms): 0.0

💡 Note: For a real patch test, run dedicated lines (flat bottom, sloped bottom, and crossing lines). The optimal offsets should make the swath perfectly symmetric.

📋 Step-by-Step Calibration Procedure (IHO S‑44)

1. Pitch Calibration

Run two opposite direction lines over a flat area. Pitch offset causes depth difference (ΔZ). Adjust until depths match.

2. Roll Calibration

Run two opposite lines over a sloping seabed. Roll error creates a "split" profile. Adjust until the two profiles align.

3. Heading (Yaw) Calibration

Use a feature (e.g., pipe, wreck) and run crossing lines. Heading error shifts the feature laterally.

4. Latency Calibration

Over a steep slope, run opposite lines. Latency creates 'bow‑wave' or 'stern‑wave' effect. Adjust until the feature is aligned.

📊 Common Offset Ranges & Tolerance

Parameter	Typical Offset	Acceptable Residual
Pitch	-0.2° to +0.2°	< 0.05°
Roll	-1.5° to +1.5°	< 0.05°
Heading	-1.0° to +1.0°	< 0.1°
Latency	-20 ms to +20 ms	< 5 ms

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Engr. Md. Rokib Hossain
Hydrographic Surveyor | 25+ years on Jamuna, Padma, Meghna | Expert in MBES calibration and river training.

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