IHO S-44 TPU Calculator – Total Propagated Uncertainty Tool
IHO S-44 Total Propagated Uncertainty (TPU) – Complete Guide + Advanced Calculator
Published by Engr. Rokib Hossain | River Warrior Academy | Updated: May 2026
🛠️ Parent Hub ERH Master Tools Hub →
📐 1. What is Total Propagated Uncertainty (TPU) and Why Does It Matter?
TPU combines all error sources affecting a depth measurement: GNSS horizontal/vertical RMS, tide uncertainty, sensor mounting offsets, and sound velocity. IHO S‑44 requires reporting both THU (Horizontal Uncertainty) and TVU (Vertical Uncertainty). Ignoring TPU can lead to rejected survey data, failed tenders, and costly re‑surveys.
THU = √(GNSS_H² + Offset²)
TVU = √(GNSS_V² + Tide²)
Total TPU = max(THU, TVU)
💡 Pro Tip: Always calculate TPU before mobilising to the field. If TPU exceeds the required IHO order, adjust your GNSS setup or tide measurement method.
📊 2. IHO S‑44 Orders – When to use which?
| Order | Max TPU (m) | Typical application |
|---|---|---|
| Special Order | ≤0.15 | Ports, harbours, critical navigation channels |
| Order 1a | ≤0.5 | Shelf seas, approach channels |
| Order 1b | >0.5 | Less critical areas, reconnaissance surveys |
🚀 3. Live TPU Calculator (IHO S‑44 Compliant)
📊 2D Uncertainty Profile (THU, TVU, TPU)
📈 2D Cross‑Section Profile (Simulated Profile)
🗺️ 3D Interactive Point Cloud (TPU Color Map)
🖱️ Drag to rotate, scroll to zoom. Hover over points to see TPU value (click on mobile).
🗜️ Batch Processing (ZIP → PDFs)
📂 4. How to Use the Calculator (Step by Step)
- Manual mode: Enter your GNSS horizontal RMS, vertical RMS, tide uncertainty and sensor offset.
- CSV upload for 3D: Upload a CSV with Easting, Northing, Tide to generate a color‑coded 3D point cloud.
- Compute TPU: Click “Compute TPU” – the 2D bar chart and profile plot update instantly.
- Change units: Select meters, feet, or yards – all outputs convert automatically.
- PDF Report: Click “PDF Report” to download a summary with both 2D and 3D snapshots.
- Batch processing: Zip multiple CSV files, upload, and get a ZIP with individual PDF reports.
- Reset: Use “Reset All” to restore default values.
📈 5. Real‑World Example
Survey vessel in the Bay of Bengal:
Horizontal RMS = 0.05 m, Vertical RMS = 0.10 m, Tide uncertainty = 0.02 m, Sensor offset = 0.03 m.
THU = √(0.05² + 0.03²) = 0.058 m
TVU = √(0.10² + 0.02²) = 0.102 m
TPU = max(0.058, 0.102) = 0.102 m → IHO Special Order compliant.
🔥 What if TPU exceeds the limit? Reduce GNSS baseline length, use dual‑frequency receivers, or apply real‑time tide corrections. The calculator helps you test “what‑if” scenarios.
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