Altimeter sea level data are crucial for various climate change studies including adaptation and disaster risk research. Meanwhile, when approaching the coastal, the accuracy of altimeter sea level data decrease due to land contamination, specular reflection and inhomogeneity of the surface. Numerous re-trackers with different strategies have been developed in order to obtain the highest possible accuracy of sea level data in coastal areas.
This study examines coastal sea level data of Jason-2 from ten re-trackers (MLE4, OCOG, Ice, Threshold, Improved Threshold, Modified CAWRES, Ice3, Oce3, Red3, and X-TRACK/ALES). Four years and a quarter data, from February 2011 to May 2015, are assessed within 20 km from the coast over five experimental regions in Indonesia. This evaluation is conducted by comparing the re-tracked sea level with in-situ tide gauge (TG) data, as well assessing the available data. The results show that of all the re-tracker applied, X-TRACK-ALES offers the highest percentage of available data in all observation regions (up to 97%) and brings reliable data up to 3.6 km to the coast. The comparison to TG results confirms that the coastal altimetry product leads to the improvement of coastal total water level envelope quality, with correlation of up to 0.98 and root mean squre error of up to 11 cm from Ice3 and X-TRACK/ALES. However, in terms of sea level anomaly, present global tidal and dynamic atmospheric corrections remain inadequate for the study areas. Based on the findings, it can be concluded that although re-tracked sea levels from X-TRACK/ALES and Ice3 have high potential for use in related application research, geophysical correction is still challenging in Indonesian coastal regions.