Faculty of Maritime Studies, King Abdulaziz University

Comparing RTK and PPK
Accuracy in Hydrographic
Surveys

KAU Hydrography survey vessel

By :
Odai Ajlan
Khalid Al Mufarrih

SUPERVISORS :
Prof. Dr. Mohamed Elsobeiey
Eng. Sultan Al Harbi

Objectives & Area

Location: Bayada region, Jeddah, Red Sea.

Goal: Compare RTK vs. PPK bathymetric accuracy using a Multibeam Echosounder (MBES).

Methodology

  • A single field survey feeding two parallel positioning workflows (RTK & PPK).
  • Processed and compared side-by-side using CARIS HIPS & SIPS.

Key Contribution

PPK as a highly reliable alternative that ensures continuous data acquisition without compromising accuracy.

Survey Standards

Evaluated according to the IHO S-44 minimum standards for hydrographic surveys.

Field Equipment

  1. Vessel: KAU Hydrography
  2. Sonar: Kongsberg EM712 MBES.
  3. Motion Sensor: Applanix POS MV Ocean Master.
  4. GNSS Bases: SinoGNSS N3 (RTK) and Trimble SPS 855 (PPK).
  5. Profiler: Sound Velocity Profiler (SVP)
Two GNSS bases on tripods at the waterfront Applanix POS MV motion and positioning equipment with Trimble antennas

Survey & Challenges

Coverage : 2152 m × 1837 m, using 7 survey lines with 20% overlap.

Field Challenges :

  • Calibration: No formal system calibration was performed.
  • SVP Limit: Rope was 50 m for a 118 m depth, requiring software extrapolation.
  • Navigation: Vessel drifted off planned lines in some areas, introducing noise. A shallow region was also left uncovered, creating a surface gap.

Data Processing

Software Used :

Applanix POSPac and CARIS HIPS & SIPS.

RTK Processing : MBES data directly georeferenced using real-time base corrections.

PPK Processing: Raw data logged and processed in POSPac to generate an SBET (Smoothed Best Estimate of Trajectory), then applied to the bathymetry.

Analysis : A surface-to-surface difference tool compared the final RTK and PPK gridded surfaces.

Final Results & Conclusion

Difference Statistics:

Mean Difference: −0.0 m.

Standard Deviation: 0.0 m.

Extreme differences (7.2 m, −5.3 m) were localized outliers on steep slopes.

Conclusion

The near-zero mean and standard deviation indicate close agreement between the real-time RTK and post-processed PPK surfaces in this survey.

Recommendation: RTK is highly reliable and time-efficient for hydrographic surveying in Bayada, though keeping PPK as a background backup is best practice.

About the reported precision

The statistics are shown at the brochure's one-decimal precision. Rounded zeros do not establish identical accuracy; unrounded values were not supplied.

THANKS

Project figure

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