Waveform identification and retracking analyses of Jason-2 altimeter satellite data for improving sea surface height estimation in Southern Java Island Waters and Java Sea, Indonesia

Abstract

Abstract. Indonesian waters containing many small islands and shallow waters leads to a less accurate of sea surface height (SSH) estimation from satellite altimetry. Little efforts are also given for the validation of SSH estimation from the satellite in Indonesian waters. The purpose of this research was to identify and retrack waveforms of Jason-2 altimeter satellite data in southern Java island waters and Java Sea using several retrackers and performed improvement percentage analyses for new SSH estimation. The study used data of the Sensor Geophysical Data Record type D (SGDR-D) of Jason-2 satellite altimeter of the year 2010 in the southern Java island waters and 2012-2014 in Java Sea. Waveform retracking analyses were conducted using several retrackers (Offset Center of Gravity, Ice, Threshold, and Improved Threshold) and examined using a world reference undulation geoid of EGM08 and Oceanic retracker. Result showed that shape and pattern of waveforms were varied in all passes, seasons, and locations specifically along the coastal regions. In general, non-Brownish and complex waveforms were identified along coastal region specifically within the distance of 0-10 km from the shoreline. In contrary, generally Brownish waveforms were found in offshore. However, Brownish waveform can also be found within coastal region and non-Brownish waveforms within offshore region. The results were also showed that the four retrackers produced a better SSH estimation in coastal region. However, there was no dominant retracker to improve the accuracy of the SSH estimate.

Waveform Classification and Retracking of Jason-2 and Jason-3 in Halmahera Sea

“…They were found in near bay and small islands that had shallow waters (<200 m) and were close to the coastline (<17 km). Several studies in other regions reported similar findings, in which the peaky waveforms were found near to the coastline [8,25,29,46,47]. [8] also found that the highest percentage of peaky waveform was onshore, 5-6 km from the coastline.…”

“…Over the Indonesian seas, previous studies (e.g., [23,25,28,29]) reported the performance of several retrackers using the geoidal height data, which highlighting the precision of retracked SSHs. While the accuracy of the retrackers is also valuable, such studies are yet to be done, thus becoming the motivation of this study.…”

“…These produced different noise levels in the waveform. Previous results in the Java Sea [25] showed that the higher the complexity of coastline topography, the more complicated the waveform shapes. [22] also reported that altimetry waveform depends on the distance between the altimeter footprint and the coastline, the type of the coastal terrains, and the shape of shorelines.…”

“…However, it seemed that the percentage of Brown class over the study site was extremely lower when compared to other study regions in Southeast Asia. For example, the percentage of Brown waveforms >90% [24] over the South China Sea, ~94% [25] over Java Sea, and 95% [29] over Natuna Sea. Furthermore, [45] found 91% non-ocean like waveforms of Sentinel-3A Synthetic Aperture Radar (SAR) altimetry over the marginal seas at Southeast Asia.…”

“…Across Southeast Asia, several studies have been conducted to assess the retracking performance over the marginal seas [11,20,23,24,25,26,27,28,29]. The performance can be determined by comparing with geoidal height data and tide gauge data.…”