Dynamics of Suspended Particulate Matter in the Changjiang Estuary from the Geostationary Ocean Color Images
Abstract
The suspended particulate matter (SPM) in Changjiang Estuary (CJE) is characterized by high concentration and significant diurnal dynamics. Due to the insufficient temporal and spatial resolution of field measurements and present satellite sensors working in polar orbit, no efficient data can be used in monitoring SPM variation from diurnal to larger temporal scales. Here, with eight hourly images obtained from the geostationary Ocean Color Imager (GOCI) per day, we circumvented this difficulty and studied diurnal and monthly changes of the SPM concentration in the Changjiang Estuary throughout 2016. Prior to computation of SPM concentration with remote sensing reflectance (Rrs), we compared the Rrs derived from the standard atmospheric correction algorithm (GOCI-AC) and the ultraviolet wavelength based algorithm (UV-AC) with field spectral data collecting during cruises and the results showed that the UV-AC method has a better performance in Rrs calculation in turbid coastal areas. We also found that the sensitive bands varied with SPM concentration, blue band for slightly and moderately turbid waters and near infrared band (NIR) for highly and extremely turbid waters. Therefore, an empirical model was established based on the correlation between field measured SPM concentration and the band ratio of Rrs745 divided by Rrs490 and proven effective in SPM estimation (R2=0.9376, RMSE=89.32 mg/l) for the Changjiang Estuary. The validation results from field data (N=12, RMSE=100.16 mg/l, MARE=41.4%) and matching pairs between GOCI-derived Rrs and in situ SPM concentration (N=28, RMSE=27.04 mg/l, MARE=32.17%) further approved its potential capability to estimate SPM concentration in a wide range. The hourly observations from GOCI showed that the diurnal variation magnitudes exhibited clear regional characteristics, with a maximum in the turbidity belt near the mouth and a minimum in the offshore deeper areas. In addition, comparing the monthly averaged SPM distribution with the amount of sediment discharged into the estuary and the remotely observed surface wind at the corresponding time, the variation in estuarine turbidity maximum zone is more likely contributed by the sediments resuspended from the sea bed that has already accumulated in the estuarine delta. This research was supported by the National Natural Science Foundation of China (41530960).
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMEP23E2374S
- Keywords:
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- 4217 Coastal processes;
- OCEANOGRAPHY: GENERALDE: 4235 Estuarine processes;
- OCEANOGRAPHY: GENERALDE: 4275 Remote sensing and electromagnetic processes;
- OCEANOGRAPHY: GENERALDE: 4546 Nearshore processes;
- OCEANOGRAPHY: PHYSICAL