Analysis and Comparison of Mean Sea Level Discrepancy in Manila and Legazpi Bays using Geodetic Leveling, Gravity Field and Oceanographic Approaches


  • Rosalie Bandojo Reyes University of the Philippines
  • Gerard Carpena
  • Xavier Zaragosa



Geodetic leveling, Gravity field model, Mean Sea Level, Mean Sea Surface, Orthometric height, Unification of vertical datum


The determination of the mean sea level (MSL) is very important in geodetic measurements. However, the accelerating rise in sea level brought about by climate change introduces uncertainties in present observations. While the effects of accelerated sea level rise vary according to geographical location, local climatological and geophysical conditions (e.g. geodynamics or tectonic activities) may contribute significantly to its overall effect. This effect may result to elevations that are not homogeneously distributed throughout the country, meaning that benchmark height determined from two different reference MSLs will give different values.


Geodetic leveling is the classical approach in propagating heights landward but this is not applicable on lands separated by large bodies of water. This is a problem for an archipelagic country such as the Philippines. As an alternative to geodetic leveling approach, gravity field and oceanographic approaches were tested to determine the discrepancy between local MSLs. The results from these alternative approaches were compared with the result of the geodetic leveling approach that was used for validation. The MSLs used for Manila and Legazpi Bays were the averaging of 19 years tidal observations from 1990-2008 and 1989-2007 respectively.

Based on the results of this study, the MSL in Manila Bay is higher by 23.6 cm than the MSL in Legazpi Bay determined from geodetic leveling approach. The oceanographic approach showed a 19.5 cm difference between the two bays, which is 4.1 cm off with the with geodetic leveling approach value. Among the three gravity field models evaluated, EIGEN-6C4 gave the closest value to the geodetic leveling approach computed MSL difference. The gravity field approach computed difference between the two locations is 24.2 cm, which differs by only 0.6 cm than the geodetic leveling approach value. Therefore, it can be concluded that the gravity field approach can be used as an alternative method to for inter-island height unification. However, further investigation should be conducted since only two locations were considered.

Author Biography

Rosalie Bandojo Reyes, University of the Philippines

Asst. Professor

Department of Geodetic Engineering


W. Torge, Geodesy, An Introduction. Berlin.New York, Walter de Gruyter, 1980.

P. Vanicek and E. J. Krakiwsky, Geodesy: The Concepts, North Holland, 1986.

R. H. Rapp, Geometric Geodesy Part II: Department of Geodetic Science and Surveying, Ohio State University, 1993.

T. H. Meyer, et al., What Does Height Really Mean? Part I: Introduction, 2004.

G. Bomford, Geodesy. New York: Oxford University Press, 1980.

J. Ihde, Inter-Commission Project 1.2: Vertical Reference Frames Report for the Period 2003 – 2007" IAG, Commission Report 2007.

R. Forsberg, et al., "Geoid model of the Philippines from airborne and surface gravity", 2014.

J. Ihde, et al., "Realization of a global unified height system and its advances for hydrographic survey and for coastal mappingâ€, Hydro 2010; Rostock-Warnemunde, Germany.

J. H. Kwon, "Gravity and World Height systemâ€, Reference Frame in Practice, 2013; Manila, Philippines.

R. Perez, et al., "Potential impacts of sea level rise on the coastal resources of Manila Bay: A preliminary vulnerability assessmentâ€, Journal of Water, Air and Soil Pollution, vol. 92, pp. 137-147, 1996.

N. K. Pavlis, et al., "An Earth Gravitational Model to Degree 2160: EGM 2008â€, General Assembly of the European Geosciences Union, April 13-18, 2008; Vienna, Austria.

C. Forste, et al., "EIGEN-6C4: The latest combined global gravity field model including GOCE data up to degree and order 2190â€, 5th GOCE User Workshop, 2014; Paris, France.

O. B. Andersen and P. Knudsen, "The DTU10 mean sea surface and mean dynamic topography: Improvements in the Arctic and coastal zonesâ€, OSTST 2010 meeting, 2010; Lisbon, Portugal.

NGS, "Geodetic Glossary," ed, 2009.

P. Vanicek and N. T. Christou, “Geoid and Its Geophysical Interpretationsâ€, CRC Press. Boca Raton, Florida, USA, 1994.

F. Sanso, et al., “Geoid and sea surface topography from satellite ground data in the Mediterranean regionâ€, Bulletin of Geodesy and Geomatics, pp. 155-201, 2008.

K. Rodulfo and F. Siringan, “Global sea level rise is recognized, but flooding from anthropogenic land subsidence is ignored around northern Manila Bay, Philippinesâ€, Disasters, vol. 30, no. 1, pp. 118−139, 2006.

T. Deguchi, Y. Kinugasa and K. Kurita, “Monitoring of Land Deformation Using Terra SAR-X Data around Active Fault in the Metro Manila, the Philippinesâ€, FIG Working Week 2011Bridging the Gap between Cultures, 18-22 May 2011; Marrakech, Morocco.

M. Véronneau and J. Huang, “The Canadian Geodetic Vertical Datum of 2013†A modernized Reference for Heights Height System Unification with GOCE, 19-20 February 2013; Noordwijk, Netherlands.

M. Filmer and W. Featherstone, A Re-Evaluation of the Offset in the Australian Height Datum Between Mainland Australia and Tasmaniaâ€, Marine Geodesy, vol. 35, no.1, pp. 107-119, 2012.




How to Cite

Reyes, R. B., Carpena, G., & Zaragosa, X. (2017). Analysis and Comparison of Mean Sea Level Discrepancy in Manila and Legazpi Bays using Geodetic Leveling, Gravity Field and Oceanographic Approaches. Asian Journal of Engineering and Technology, 5(2).