| The evolution characteristics of estuarine and coastal morphology are being moulded by the complicated hydrodynamic factors. The transport of sea surface sediment is the bridge between kinetic factors and geomorphology development. Therefore, how to use the combination of different temporal, spatial-resolution, electromagnetic wave and active and passive remote sensing images to routinely observe and analyze various environment kinetic parameters? This is a new challenge for the application of oceanic remote sensing. Based on these issues, multi-source remote sensing images, auxiliary meteorological data, in situ data and numerical simulation data are selected to construct the retrieval algorithms of various sea surface parameters in the estuarine and coastal area. In addition, the retrieved products are validated with the numerical simulated results in order to demonstrate the reliability of the algorithms. We further analyze and discuss the temporal and spatial distribution of SSC (Suspended Sediment Concentration) under comprehensive effect of various hydrodynamic interactions and its dynamic mechanism from the point of multi-source remote sensing. This study will consequentially help to better understand the features of land-ocean interactions; and provide scientific and reasonable data for estuarine and coastal engineering, sedimentary geomorphic evolution and ecological environmental protection. The major research contents are as follows.1) Sea surface wind retrieval based on SARERS2-SAR, ENVISAT-ASAR data are selected to extract high-resolution and high-precision sea surface wind through the improved2D FFT and CMOD4model. SAR-retrieved wind fields are validated with collocated measurements from QuikSCAT and products from the atmospheric Weather Research Forecasting model (WRF). In general, we found good agreement between the datasets, indicating the reliability and applicability of SAR-retrieved algorithms under different atmospheric conditions. Although QuikSCAT can only produce wind vectors with resolution up to12.5km, it is still best suited for open ocean measurements. In coastal regions, where wind fields can vary dramatically over a few km, SAR images are able to offer sub-km resolution. Therefore, we can obtain an improved global wind product by combining QuikSCAT wind products in open ocean areas with high-resolution SAR-retrieved wind fields in coastal areas. Moreover, we discussed the main inherent error sources in the process, and conducted sensitivity analyses using CMOD4to estimate the error caused by the effect of speckle, uncertainty in wind direction, and inaccuracy in normalized radar cross section (NRCS). For the high speed wind, e.g., typhoon, CMOD5model is applied and demonstrated to have the strong capability, including determination of typhoon center position, typhoon spatial structure and typhoon wind speed. These will be very helpful for the marine severe weather prediction. Finally, SAR-retrieved wind fields were applied to simulate the salinity distribution off the Changjiang estuary. The findings of this study will be valuable for wind resource assessment and development of future numerical ocean models based on SAR images.2) Sea surface velocity retrieval based on ASARBased on the Doppler centroid anomaly theory, ENVISAT-ASAR images are applied to derive the sea surface Doppler velocity. Yet, biases contaminate the Doppler centroid shift that, in turn, affect the retrieval of the range Doppler velocity. Careful corrections and bias removal is therefore highly needed to retrieve reliable signals. Azimuth bias removal from the scene NRCS gradients and range bias removal from reference data have been presented for three different ASAR scenes at Yangtze Estuary. The RMS offset of the corrected Doppler anomaly is approximately to6.0Hz, corresponding to a horizontal Doppler velocity of29cm/s at35°incidence angle. In this study, the Doppler method yields estimates with a resolution (azimuth, range) of about8km×4km and substantial overlaps. The orientation of the ENVISAT-ASAR tracks with respect to the Changjiang River outflow implies that the descending tracks are most attractive for the range Doppler shift observation. Uncertainty analysis of ASAR Doppler velocity are also discussed with regard to the strong azimuthal NRCS gradients, low radar incidence angle, inaccuracy in wind field and the presence of rain cells. The ASAR surface current velocities are particularly sensitive to inaccuracies in the wind correction. 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. The Doppler measurements therefore have the capability to derive innovative estimates of surface velocities at Yangtze Estuary. These Doppler based velocity retrievals from ASAR images of the Yangtze Estuary area are valuable as they reveal the multi-scale dynamics around the East China Sea. Furthermore, the ASAR Doppler velocities have the capability to provide sufficiently accurate spatial information for validation of high resolution coastal models.3) Suspended Sediment Concentration retrieval based on MERISThe SERT model coupled with a multi-conditional algorithm scheme is introduced and validated with in situ measurements using MERIS-in situ data matchups. The results are considerably accurate and reliable. Spatially, the SSC from Xuliujing downward to the turbidity maximum to Hangzhou Bay increases constantly under normal conditions; SSC during spring tide is larger than that in ordinary tide than that in neap tide. SSC in Yangtze estuary presents significant seasonal changes, in the inner estuary it showing higher concentration during summer than during w. inter; while in the outer estuary it presenting higher concentration during winter than during summer. In the North Passage and South Passage regions, SSC reveals unobvious seasonal changes and exists a transformation trade; sometimes it shows higher concentration during winter than during summer, sometimes it is the other way around. Temporally, the SSC show a neap-spring tidal cycle and seasonal fluctuations.4) Driving factors research on Yangtze suspended sediment distributionBased on multi-source remote sensing data, meteorological data and in situ data, we discuss the main driving factors of Yangtze suspended sediment distribution. It is concluded that Yangtze runoff control sediment distribution in the inner estuary; tidal currents are the predominant factors related to sediment distribution in the outer estuary and Hangzhou Bay areas; wind direction and wind speed control the diffusion area of SSC. |
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