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Addendum published on 4 July 2018, see Remote Sens. 2018, 10(7), 1059.

Open AccessArticle

Evaluation of Coastal Sea Level Offshore Hong Kong from Jason-2 Altimetry

The CAS Key Laboratory of Microwave Remote Sensing, National Space Science Center, Chinese Academy of Sciences, Beijing 100190, China
Laboratoire d’Etudes en Géophysique et Océanographie Spatiales (LEGOS), Observatoire Midi-Pyrénées, 31400 Toulouse, France
State Key Laboratory of Remote Sensing Science, Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences, Beijing 100094, China
International Space Science Institute, 3102 Bern, Switzerland
Author to whom correspondence should be addressed.
Remote Sens. 2018, 10(2), 282;
Received: 23 November 2017 / Revised: 2 February 2018 / Accepted: 6 February 2018 / Published: 12 February 2018
(This article belongs to the Special Issue Satellite Altimetry for Earth Sciences)
PDF [5401 KB, uploaded 9 July 2018]


As altimeter satellites approach coastal areas, the number of valid sea surface height measurements decrease dramatically because of land contamination. In recent years, different methodologies have been developed to recover data within 10–20 km from the coast. These include computation of geophysical corrections adapted to the coastal zone and retracking of raw radar echoes. In this paper, we combine for the first time coastal geophysical corrections and retracking along a Jason-2 satellite pass that crosses the coast near the Hong-Kong tide gauge. Six years and a half of data are analyzed, from July 2008 to December 2014 (orbital cycles 1–238). Different retrackers are considered, including the ALES retracker and the different retrackers of the PISTACH products. For each retracker, we evaluate the quality of the recovered sea surface height by comparing with data from the Hong Kong tide gauge (located 10 km away). We analyze the impact of the different geophysical corrections available on the result. We also compute sea surface height bias and noise over both open ocean (>10 km away from coast) and coastal zone (within 10 km or 5 km coast-ward). The study shows that, in the Hong Kong area, after outlier removal, the ALES retracker performs better in the coastal zone than the other retrackers, both in terms of noise level and trend uncertainty. It also shows that the choice of the ocean tide solution has a great impact on the results, while the wet troposphere correction has little influence. By comparing short-term trends computed over the 2008.5–2014 time span, both in the coastal zone and in the open ocean (using the Climate Change Initiative sea level data as a reference), we find that the coastal sea level trend is about twice the one observed further offshore. It suggests that in the Hong Kong region, the short-term sea level trend significantly increases when approaching the coast. View Full-Text
Keywords: Jason-2; Hong Kong coast; retracking; X-TRACK; ALES; PISTACH Jason-2; Hong Kong coast; retracking; X-TRACK; ALES; PISTACH

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Xu, X.-Y.; Birol, F.; Cazenave, A. Evaluation of Coastal Sea Level Offshore Hong Kong from Jason-2 Altimetry. Remote Sens. 2018, 10, 282.

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