Modernisation of the Philippine Height System

Abstract

The Philippine Height System (PHS) modernisation is driven by recent advances in geodetic technology and the Philippines’ need to be geodetically responsive to natural disasters. Aspects of the shift from a levelling-based system to a GNSS and gravimetric geoid-based system, being a cost-effective modernisation strategy for developing countries, were investigated. This thesis expands available scientific literature for the International Height Reference System/Frame (IHRS/F) development of the International Association of Geodesy (IAG), and the PHS modernisation efforts of the National Mapping and Resource Information Authority (NAMRIA). Three elements of a modern PHS were studied. 1. The engineering implications of the new Philippine Geoid Model (PGM). 2. The temporal variability of the geoid and benchmarks with focus on the effects of tropical hydrology. 3. The PHS relationship to the IHRS/F.

An evaluation of the new Technical University of Denmark (DTU-Space) and NAMRIA-developed PGM, was done to provide a quality baseline for managing the progression and limitations of a gravimetric geoid-based height system for the country. Statistical measures show that points clustered in the southern latitudes and eastern longitudes have relatively higher residuals due to geodynamic and hydrologic activity. It is concluded that a localised PGM can be used for third order applications.

Tropical effects on the reference frame and the geoid were examined. Displacements were analysed by estimating tidal and non-tidal loading for selected Philippine active geodetic stations using rain sensor data, local geologic information and ground validation. The mean dynamic topography (MDT) was also investigated. DTU10, VM500-ph and RADS-ph were compared with GNSS-geoid MDTs (GNSS-PGM2016.66, GNSS-EIGENGL05C). A nationwide scale, low-resolution Philippine vertical ground motion map inferred from Sentinel-1A scenes from January 2015 to December 2019 was also produced. Estimations confirm the intensity of land motion in the eastern and southern part of the country. Using Gravity Recovery and Climate Experiment (GRACE) temporal models, large variations for two IHRS/F-proposed Philippine stations were computed and show coincidence with high rainfall records. A causality relationship between high rainfall and geoid variation, however, is inconclusive.

Lastly, a novel way of characterising local height systems relationship for the IHRS/F that takes into account the non-homogenous states of geodetic development within a developing, archipelagic country is introduced. Recommendations for a modernised Philippine Height System were made as a result of this study.