High-resolution depth and coastline over major atolls of South China Sea from satellite altimetry and imagery

• Published in: Remote sensing of environment 2016-04, Vol.176, p.69-83
• Main Authors: Hsiao, Yu-Shen, Hwang, Cheinway, Cheng, Yung-Sheng, Chen, Liang-Chien, Hsu, Hung-Jui, Tsai, Jung-Huo, Liu, Chien-Liang, Wang, Ching-Chieh, Liu, Ya-Chi, Kao, Yu-Chi
• Format: Article
• Language: English
• Subjects: Altimeters; Atoll depth; Atolls; China; Coastlines; Gravitation; Gravity; Gravity anomalies; Ocean models; Satellite altimetry; Satellite imagery; South China Sea
• ISSN: 0034-4257; 1879-0704
• DOI: 10.1016/j.rse.2016.01.016

Current bathymetric models for the South China Sea (SCS) are largely based on predicted depths from gravity and sparse single-beam echo-sounder measurements. Such models lack high-resolution coastlines and shallow-water bottom features around atolls and islands. This study refines the gravity field of the SCS using sea surface heights from measurements of satellite altimeter Geosat/GM, ERS-1/GM, Jason-1/GM and the original Cryosat-2. A new one-minute gravity anomaly grid is determined. The modeled gravity anomalies show a 6-mgal RMS discrepancy with shipborne measurements in shallow waters. An altimeter-only bathymetric model is derived from the new gravity grid by the gravity-geological method that uses the latest global and regional models of the ocean depth and marine gravity as a priori knowledge. The new model outperforms current SCS bathymetric models and is accurate to 100m, based on comparison with multi-beam depth measurements. Optical images from IKONOS-2, QuickBird-2, GeoEye-1, WorldView-1-2 and -3, are rectified and digitized to derive the zero (coastline) and 20-m depth contours (reef lines) around 44 atolls, which are integrated with the altimeter-only depths, giving significantly improved accuracies and spatial resolutions in modeled depths. The improvement percentages of coastlines by the satellite imagery range from 50% to 97% at 41 of the 44 atolls. We establish a webpage for free access to the optical and depth images, and the depth and gravity grids. We will continue to update satellite images, altimeter-derived gravity grids and bathymetric models over major atolls of the SCS. •High-resolution, most accurate altimeter gravity anomalies in the South China Sea•Most accurate altimeter-only depths in the SCS, confirmed by multi-beam depths•Detailed reef lines and coastlines over atolls from satellite altimetry and imagery