Abstract
Abstract. Coupled with the occurrence of regional/local sea level rise on urbanized coastal cities is the possibility of land subsidence that contaminates the measurement by the tide gauge (TG) sensors. Another technology that could possibly check the in-situ data from tide gauge is satellite altimetry. The sea surface height (SSH) measured from satellite altimeter is compared with the observed tide gauge sea level (TGSL) to detect vertical land motion (VLM). This study used satellite altimeter retracked products near the TG Stations in Tagbilaran, Bohol; Dumaguete, Negros Oriental; and Mambajao, Camiguin located in the vicinity of the South East Bohol Trench and Fault (SEBTF).Based on the results, the TG site in Tagbilaran is undergoing land subsidence. The rate of VLM is around 5 mm/year from 2009 to 2017. The same trend was manifested in the GNSS observed data in the PHIVOLCS monitoring station in Tagbilaran and the geodetic levelling done in the area. After the October 15, 2013 earthquake in Bohol, downward trends of around 27 mm/year and 17 mm/year were observed from GNSS measurements and SSH-TGSL difference respectively. These different rates may be due to the distance between the two sensors. The comparison between SSH and TGSL in Dumaguete showed small difference with a VLM rate of 1.8 mm/year. The difference in SSH-TGSL in Mambajao is quite large with a downward rate of 9.4 mm/year. This result needs to be further investigated for TG or TGBM instability or monitored for a possibility of land uplift.
Highlights
According to the submitted report of the Working Group I to the Intergovernmental Panel on Climate Change (IPCC), the global mean sea level (GMSL) rate is 3.2 mm/year
The tide gauge sea level (TGSL) shows different average values because the tide gauge (TG) data is being matched with the measurements from satellite altimeters, but they do not vary much
TGSLs are higher than the sea surface height (SSH) determined by satellite altimeter
Summary
According to the submitted report of the Working Group I to the Intergovernmental Panel on Climate Change (IPCC), the global mean sea level (GMSL) rate is 3.2 mm/year. This is computed by the different altimetry data processing groups over 1993 to 2012 (Church, et al 2013). Recent advances in space technology, made it possible to quantify sea surface height based on a global reference surface i.e. the surface of a geocentric ellipsoid such as WGS84. This can be considered an absolute reference surface. Archived altimeter data are being reprocessed/retracked including current data acquisitions for coastal and inland waters applications
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