83:3 (2021) 107–117|https://journals.utm.my/jurnalteknologi|eISSN 2180–3722 |DOI: https://doi.org/10.11113/jurnalteknologi.v83.15125| Jurnal Teknologi Full Paper WAVEFORM CLASSIFICATION AND RETRACKING OF JASON-2 AND JASON-3 IN HALMAHERA SEA Maya Eria Sinurat a* , Bisman Nababan b , Jonson Lumban Gaol b , Henry Munandar Manik a , Nurul Hazrina Idris c,d a Marine Technology Graduate Study Program, Faculty of Fisheries & Marine Science, IPB University, Bogor, Indonesia b Department of Marine Science and Technology, Faculty of Fisheries & Marine Science, IPB University, Bogor, Indonesia c Tropical Resource Mapping Research Group, Department of Geoinformation, Faculty of Built Environment and Surveying, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor Malaysia d Geoscience and Digital Earth Centre, Research Institute for Sustainability and Environment, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor Malaysia Article history Received 21 September 2020 Received in revised form 29 March 2021 Accepted 30 March 2021 Published online 22 April 2021 *Corresponding author maya_eria@apps.ipb.ac.id Graphical abstract Abstract The accuracy of sea surface heights (SSHs) estimation from satellite altimeters is strongly influenced by the microwave reflected signals (or waveforms). Waveforms in open oceans generally have ideal shapes following the Brown (1977) model. However, in coastal and shallow waters, the signals are disturbed by lands, thus resulting in complicated waveforms (non-Brown). Non-Brown waveforms produce inaccurate SSH estimations; therefore, specialized protocols such as waveform classification and retracking are crucial when attempting to produce accurate estimations. In this study, waveforms of Jason-2 and Jason-3 satellite altimeters in the Halmahera were classified and retracked using several algorithms, such as Offset Centre of Gravity (OCOG), Ice, Threshold, and Improved Threshold. The results showed that waveforms in the Halmahera Sea had ten generic classes with dominant class of the Browns. The validation results showed that all retrackers (except OCOG) had the value of correlations exceeding 0.75, and Root Mean Square Error (RMSE) smaller than 25 cm at a distance of 5-20 km from the land. The Threshold 10% was the most common retracker that appeared with the highest improvement percentage (IMP), meanwhile the Ice retracker consistently produced the best correlation (0.86) and the lowest RMSE (16cm). The retracking results showed that waveform retracking generally can improve SSH estimation accuracy from ocean (standard) retracker. Keywords: Coastal altimetry, classification, retracking, Jason-2, Jason-3 © 2021 Penerbit UTM Press. All rights reserved 1.0 INTRODUCTION Indonesia is an archipelagic country, which contains of 17,504 islands and has long coastline of 99,093 km. Indonesia also has high variability of sea levels, thus making it vulnerable to sea level rise. The sea level rise in Indonesia is about 4.2 – 5.8 mm/year or higher up to twofold of the world sea level rise rate [1, 2, 3]. The