Effect of sea level rise in the validation of geopotential/geoid models in Metro Manila, Philippines

Abstract

The release of new global geopotential models (GGMs) has raised the question of whether these GGMs could now supplant the development of regional/local geoid models. For geodetic surveying purposes the importance of a geoid model fitted to the local condition will greatly help in the resolution of many vertical datum issues especially for an archipelagic country such as the Philippines. Since the geoid as a vertical reference surface is used to convert ellipsoidal heights acquired through GNSS survey to orthometric heights, it is vital that this should at least match the heights derived through geodetic levelling within the allowed accuracy. However, the issue of mean sea level (MSL) as vertical reference for geodetic levelling has introduced another issue of concern especially when it is exhibiting accelerated sea level rise (ASLR). The results of the validation and comparison of recent GGMs showed that EGM 2008 and the 2012 released EIGEN-6C2 both classified as combined type model have RMS around 14 and 13 cm respectively in the study area. These results were achieved when ASLR was considered in the validation. The local geoid model (LGM) developed using least squares modification of Stokes formula with additive corrections (LSMSA) approach has RMS around 11 cm using an integration cap of 3° from the limit of study area. The LGM validated the level of the combined type GGMs in reference to the local vertical datum in Manila Bay. Based on the result of this study, the ASLR contributed much to the departure of the latest MSL from the geoid.