🖥️ Day 19: Real-Time Visualization & Quality Control (QC)
📊 DAY 19: REAL‑TIME QC & DATA LOGGING
Monitor, Catch Errors Early, and Secure Your Data
Instructor: Engr. Rokib Hossain | River Warrior Academy
📖 Today's Outline
- 🎯 Why Real‑Time QC?
- 🗺️ Coverage Monitoring – Closing the Gaps
- ⚓ Motion QC – Heave, Roll, Pitch Limits
- 🛰️ GNSS Status – RTK Fix, PDOP, Satellites
- 🌊 SVP & Tide QC
- 💾 Data Logging – Settings, File Naming, Splitting
- 📀 Backup Strategies – Don’t Lose a Single Ping
- 🔗 External Resources & Tools
- 📋 Homework & Fieldwork Checklists
- ❓ Frequently Asked Questions
- ✅ Action Items & Internal Linking
🎯 Why Real‑Time QC?
Real‑time Quality Control (QC) is the process of monitoring data as it is collected to detect problems immediately. It is far cheaper to re‑run a line while still on site than to reprocess bad data later or, worse, remobilise the vessel.
Key QC objectives:
- Ensure 100% bottom coverage (MBES) or no gaps (SBES).
- Verify GNSS fix status (RTK FIX, not float).
- Monitor motion (heave, roll, pitch) against safe thresholds.
- Check sound velocity and tide corrections are applied.
- Confirm data is being logged to disk correctly.
🗺️ Coverage Monitoring – Closing the Gaps
For MBES, the coverage display (colour‑coded swath) is your most important QC tool. Lines are shown in real time. Gaps appear as white or blank areas.
What to check:
- Swath overlap: at least 20% overlap between adjacent lines.
- No missed areas: if a white gap appears, immediately re‑run that section before moving on.
- Outer beam noise: excessive spikes or striping indicates SVP problems or motion issues.
For SBES, coverage is not automatic. You must verify that line spacing is tight enough based on beam footprint. Many SBES systems provide a “bottom track” display that shows depth along the line – look for sudden dropouts.
(Replace with your own image)
⚓ Motion QC – Heave, Roll, Pitch Limits
Excessive vessel motion degrades multibeam data quality. Set alarm thresholds in your acquisition software (typical values):
- Heave: >0.3 m – may cause depth uncertainty. Stop logging if >0.5 m.
- Roll: >5° – outer beams become unreliable. >8° stop survey.
- Pitch: >3° – can affect along‑track resolution.
Monitor the real‑time motion graph. If motion exceeds limits for more than a few seconds, pause logging, change vessel heading or wait for calmer conditions.
🛰️ GNSS Status – RTK Fix, PDOP, Satellites
Without a reliable RTK FIX, your horizontal and vertical positioning is degraded (float or standalone). Essential GNSS QC parameters:
- Fix type: Must be “FIX” or “RTK Fix”. “Float” or “DGPS” reduces accuracy to decimetre or metre level – not acceptable for IHO orders.
- PDOP: <2.5 is good; <1.5 is excellent. If PDOP >4, check for obstructions or poor satellite geometry.
- Number of satellites: At least 10‑12 for dual‑frequency.
- Base station distance (if RTK): Ideally <20 km; longer baselines degrade accuracy.
If RTK fix is lost, stop logging until it returns. Continuing with float will spoil the dataset.
🌊 SVP & Tide QC
SVP QC: Ensure the correct SVP file is loaded and that its age is less than 4‑6 hours (or as required by your project). If you see depth errors increasing towards the outer beams, you may need a fresh SVP cast.
Tide QC: Verify that the real‑time tide correction (or predicted tide) is applied correctly. Compare logged depth against a known check line or a tide staff reading. A systematic depth offset indicates tide datum mismatch.
💾 Data Logging – Settings, File Naming, Splitting
Proper logging configuration ensures you can retrieve and process data later without missing files.
- File naming convention: Use a systematic pattern, e.g., `Project_YYYYMMDD_LineNN.raw`. Avoid spaces and special characters.
- File splitting: Set maximum file size (e.g., 2 GB) to prevent corruption. Modern software can split automatically while maintaining continuity.
- Log all sensors: Ensure GNSS, IMU, sonar, and SVP are all being recorded. A missing stream will break processing.
- Separate navigation log: Also log an ASCII (NMEA) file as a backup – can be used for rough checks even if raw file corrupts.
Before starting a line, always verify that the logging indicator is active (flashing red or “REC”).
📀 Backup Strategies – Don’t Lose a Single Ping
Data loss is catastrophic. Implement a 3‑2‑1 backup strategy for hydrographic surveys:
- 3 copies: One on the acquisition computer, one on an external SSD, one on a separate storage (cloud or second external drive).
- 2 different media: internal SSD + external rugged drive.
- 1 off‑site: End of each day, copy to a third drive that leaves the vessel.
Daily backup routine:
- After finishing lines, use a script or manual copy to duplicate the raw data folder to External Drive A.
- At end of day, copy to External Drive B (kept in a waterproof case).
- If internet is available, upload to cloud storage (e.g., Google Drive, Dropbox) – compress files first.
🔗 External Resources & Tools
Useful software for real‑time QC and backup automation:
| Tool | Purpose | Link |
|---|---|---|
| FreeFileSync (open source) | Automated backup and synchronisation | freefilesync.org |
📋 Homework & Fieldwork Checklists
📘 Day 19 – Homework Checklist
- ✅ Read the entire Day 19 post.
- ✅ Set up a free file synchronisation tool (FreeFileSync) and simulate backing up a folder to an external drive.
- ✅ List five QC parameters you would monitor during a MBES survey and the action you take if each fails.
- ✅ Write a one‑paragraph backup procedure for a 5‑day survey.
- ✅ Share this post with #Hydrography #RealTimeQC.
🛠️ Fieldwork Readiness Checklist – QC & Logging
- ✅ Before survey: configure QC alarms (heave, roll, pitch, RTK fix, PDOP). Test that alarms trigger properly.
- ✅ Set up logging folders with clear naming convention. Create a master logbook (digital or paper) to record line numbers, times, and QC notes.
- ✅ During survey: keep the coverage display visible at all times. Pause and re‑run any line with a gap.
- ✅ Monitor GNSS status every few minutes. If fix drops to float, stop and wait for fix.
- ✅ After each line: check that the raw file size is non‑zero and that the last ping time matches the end of line.
- ✅ End of day: backup to two external drives. Verify file integrity by copying back and comparing checksums (or using file sync tool).
- ✅ Store backup drives in separate locations (one on vessel, one taken ashore).
❓ Frequently Asked Questions
✅ Action Items & Internal Linking
🎯 Your Tasks for Today
- 📌 Step 1: Bookmark the Course Homepage and the FreeFileSync website.
- 📌 Step 2: Download the checklist PDF using the button at the top.
- 📌 Step 3: Practice creating a test backup and verifying it with checksums.
- 📌 Step 4: Leave a comment on this post: “The QC parameter I find hardest to monitor is ____ because ____.”
- 📌 Step 5: Proceed to Day 20: Data Logging Deep Dive & Storage Management using the link below.
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