Real Time Kinematic (RTK) heave as a replacement of Motion Reference Unit (MRU) heave in hydrographic surveying works

Mohammed Elmeligy, Saad Mesbah, Mohamed Mohasseb


Heave is one of the major contributors to errors in water depth measurements. Motion Reference Unit (MRU) measures the heave signal with high-level accuracy as well as other ship motions.  Unfortunately, MRU has been reported to have some of drawbacks such as; heave drift error, influence of ship motion dynamic, In addition to its very expensive price

Real-Time Kinematic (RTK) GPS uses dual frequency receiver and carrier phase differential technique under kinematic solution and provides very accurate position in all three components in real time.  In addition, RTK GPS also calculates the low frequency changes in water level such as tidal oscillation.

This research is an attempt to investigate the possibility of using the RTK GPS data to deduce the heave signal from the GPS height (tides - heave) instead of heave from MRU to correct the water depth.  Moreover, to examine to what extent, RTK heave can be used as a backup to satisfy the International Hydrographic Organization (IHO) survey order standards.

A comparison between the extracted RTK heave and MRU heave signals revealed a good agreement with a strong direct correlation of 0.96.

As shown in figure 1 RTK heave as a replacement for MRU heave in hydrographic surveying was statistically validated with the use of  a lot of methods of analysis such as Test of the Normality, Paired Samples T Test, Wilcoxon Signed Ranks Test, Heave Signals Frequency Adjustment , Descriptive Statistics for the Two Heave Signals , Descriptive Statistics for Each Signal Individually , Correlation and Trend, Analysis Between the Two Signals, Scatter Diagram and Trend, Standard Deviation and Uncertainty for Soundings, Characteristics of the Difference between Two Signals , Comparing the Surfaces by TIN Model.

The results of this analysis provided the possibility of using RTK heave as a replacement for MRU heave in hydrographic surveying. Therefore, RTK GPS is not only used to provide precise position or tidal oscillations but also based on this study, can be used to measure heave accurately to correct the depth satisfying IHO survey standards.


Received: 28 January 2023

Accepted: 26 April 2023

Published: 22 May 2023


GPS; GPS Hieght; Heave; Hypack; Hydrographic Survey; IHO; Motion Sensor; RTK GPS Heave; Tide

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- Blake, S.J. (2007). Heave Compensation Using Time-Differenced Carrier Observations from Low Cost GPS Receivers, Institute of Engineering, Surveying and Space Geodesy. Thesis submitted to the University of Nottingham for the degree of Doctor of Philosophy June 2007pages 8, 58, 59, 66, 70, 72, 73, and 92.

- Böder, V.( 2008). Investigation of Attitude Sensors for Hydrographic Applications.

- Caldwell, J.M. (1955). "The Step Resistance Wave Gauge."Proceedings of the First Conference on Coastal Engineering Instruments. Berkeley, California, Oct 31 -Nov. 2, 1955, pp 44-60.

- Chang, C.C. and Lee, H.W. and Tsui, I.F. (2002). Preliminary test of tide-independent bathymetric measurement based on GPS, Department of Surveying and Mapping Engineering, Chung Cheng Institute of Technology Tahsi, Taoyuan 335, Taiwan, ROC, Naval Hydrographic and Oceanographic Office, page 2.

- El-Assal, Ashraf N., A. El-Rabbany and Saad M. Abdelrahman (2009). On spectral fusion of GPS and heave data in support of Multibeam hydrographic surveying. HYDR09, Cape Town, South Africa, Nov.2009.

- Godhavn, J. M. (2000). High quality heave measurement based on GPS RTK and accelerometer technology. Oceans 2000 MTS/IEEE Conference Proceeding, V. 3 (11-14 Sep, 2000), p. 1,309 - 314.

- Grover, S.C. (1954)."Observations on Ship Motions at Sea."Proceedings of the First Conference on Ships and Waves. Hoboken, New Jersey, October, 1954, pp 351- 363.

- IHO (2005): Manual of hydrography Publication M13 fifth edition, 2008, Pages15, 92, 93, 94, 95, 96, 132,169,170.275.

- IHO (2008): IHO standards for hydrographic survey, 4th Edition, 2008, Special Publication No. 44 by the International Hydrographic Bureau, Monaco.

- Kielland, P., Hagglund, J., 1995. Using DGPS to measure the heave motion of hydrographic survey vessels. In: Institute of Navigation NTM 95.

- OMC INTERNATIONAL.(2005). INDYNAMIC UNDER KEEL CLEARANCE, Marine Services Department, page 4.

- Rabah M. and El Hattab.A (2010): “Developing a Real Time Algorithm for Heave Determination Based on Single Frequency GPS Data”, Maritime Scientific Research Journal, Issue No. 1, Vol. No.1, pp. 40-48.

- Rapatz, P.J.V. (1991).Vessel Heave Determination Using the Global Positioning System. M.Sc.E. thesis, Department of Surveying Engineering Technical Report No. 155, University of New Brunswick, Fredericton, New Brunswick, Canada, pages 3,4,12,18,19.

- (, and Kongsberg). [Accessed on 20thAug 2014].



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Maritime Research and Technology
E-ISSN: 2812-5622
P-ISSN: 2812-5614 

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Arab Academy for Science, Technology and Maritime Transport (AASTMT)
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