Investigating Coastal Zone and Open Ocean Dynamics and Bio-Optical Conditions by Satellite Sensor Synergy in Combination with In-Situ Data and Simulation Models
1) Sea surface wind retrieval based on SAR
ERS2-SAR and ENVISAT-ASAR data were selected to extract high-resolution and high-precision sea surface wind in Changjiang Estuary through the improved 2D FFT and CMOD4 models. SAR-retrieved wind fields are validated with collocated measurements from QuikSCAT and products from the atmospheric Weather Research Forecasting model (WRF). SAR-retrieved wind fields were applied to simulate the salinity distribution off the Changjiang estuary.
2) Sea surface velocity retrieval based on ASAR
Based on the Doppler centroid anomaly theory, ENVISAT-ASAR images were applied to derive the sea surface Doppler velocity in the Changjiang Estuary. The RMS offset of the corrected Doppler anomaly is approximately to 6.0 Hz, corresponding to a horizontal Doppler velocity of 29 cm/s at 35º incidence angle. Using wind fields accurately retrieved from the ASAR images yield the most accurate retrieval of the ASAR surface current. The inter-comparison and validation of the ASAR-derived Doppler velocities against the surface velocity field derived from numerical ocean model simulations shows promising results.
3) SAR Simulations of Bathymetry
With synchronized in-situ observations and numerical simulations, a sea surface wave and current interaction model was established to describe the interaction between the sea surface current and sea surface micro scale wave. The model was used to derive an accurate sea surface current. In addition, a fully 2-D system that integrates the coastal ocean model and a radar imaging model (RIM), for imaging bathymetric changes，was developed and tested. The results show that variations in the simulated image intensity are mainly dominated by distinct radar backscatter anomalies caused by wave-current interactions in the vicinity of rapidly changing underwater topographies. The comparison between the simulated and observed synthetic aperture radar (SAR) images shows reasonable agreement.
Dr. Vladimir Kudryavtsev, Dr. Xiaojing Zhong, Dr. Jianzhong Ge, Dr. Jianrong Zhu and Dr. Bo Tian from NERSC and SKLEC have also contributed some of their work in this project.
Wang Lihua, Zhou Yunxuan, Ge Jianzhong, Johnny A Johannessen, Shen Fang, 2014. Mapping sea surface velocities in the Yangtze coastal zone with ASAR. Acta Oceanologica Sinica. 33(11):141-149
Wang Lihua, Zhou Yunxuan, Zhu Jianrong, Shen Fang, Tianbo, 2014. Deriving Changjiang coastal zone wind from C-band SAR and its application to salinity simulation. Chinese Journal of Oceanology and Limnology. 32(4):946-957
Peng Yu, Johnny Johannessen, Vladimir Kudryavtsev, Xiaojing Zhong, Yunxuan Zhou, 2016. Monitoring Changes in Estuarine Bathymetry Based on SAR Observations: A Case Study in the Yangtze Estuary (to be submitted)