The spatial distribution of salinity in the Pearl River Estuary in China from space

Sea surface salinity of ocean waters has been obtained from L-band microwave radiometer on satellite, such SMOS, Aquarius and SMAP. It provides a new technology and way to observe the salinity over large region from space. However, it is still difficult to get the sea surface salinity of the coastal waters due to that the effect on satellite-observed microwave radiance of radio frequency interference over near-shore regions. Fortunately, the colored dissolved organic matter (CDOM) has conservative or semi-conservative property in the freshwater areas of coastal rivers and it has a good linear correlation between the absorption coefficient of CDOM and salinity. Based on those, a conservative mixing relationship between the fresh water from the Pearl River and the sea water from the South China Sea are established and the distribution of sea surface salinity from MODIS-retrieved absorption coefficient of CDOM (aCDOM) at 355nm wavelength in this study. The linear relationship between salinity and aCDOM at 355 nm under conservative mixing conditions can be established from the in-situ observed salinity and MODIS-retrieved aCDOM at 355 nm at the central water mass in the Pearl River Estuary and the northern basin region of South China Sea. By comparing daily observed MODIS-retrieved sea surface salinity with the in-site observed salinity, it shows that the salinity retrieved from satellite-based aCDOM has good agreement with observations, and it can better capture the location of low salinity fresh water in the Pearl River. For the summer averaged satellite-based salinity from 2002 to 2018, sea surface salinity are gradually increases from the vertical coastline to the sea in the Pearl River Estuary region. The salinity in coastal region is low by the effect of the Pearl River diluted water, and the salinity in offshore region is high. On average, the distribution of salinity shows that the diffusion of fresh water from the Pearl River generally spread along the coastline to the east and west in summer, while the runoff on the westward is larger and on the eastward it is affected by some flushing water of other rivers. In the future, MODIS-retrieved salinity can be as a supplement to salinity inversion of Microwave radiometer in the coastal region.

[1]  Fugui Wang,et al.  Development and application of a remote sensing-based salinity prediction model for a large estuarine lake in the US Gulf of Mexico coast , 2008 .

[2]  X. Yin,et al.  Spectral Analysis on Sub-Tidal Variability of Salinity in Modaomen Waterway of Pearl River Estuary, China , 2012 .

[3]  Joel T. Johnson,et al.  SMAP L-Band Microwave Radiometer: RFI Mitigation Prelaunch Analysis and First Year On-Orbit Observations , 2016, IEEE Transactions on Geoscience and Remote Sensing.

[4]  F. Hellweger,et al.  Tracing Amazon River water into the Caribbean Sea , 2002 .

[5]  C.E. Everard,et al.  Oceanography , 1963, Journal of Navigation.

[6]  Yann Kerr,et al.  The SMOS Mission: New Tool for Monitoring Key Elements ofthe Global Water Cycle , 2010, Proceedings of the IEEE.

[7]  P. Divakaran,et al.  The theoretical impact of remotely sensed sea surface salinity observations in a multi-variate assimilation system , 2009 .

[8]  B. Cui,et al.  Retrieval of remotely sensed sea surface salinity using MODIS data in the Chinese Bohai Sea , 2017 .

[9]  Siamak Khorram,et al.  Remote sensing of salinity in the San Francisco Bay Delta , 1982 .

[10]  Yan Bai,et al.  Remote sensing of salinity from satellite-derived CDOM in the Changjiang River dominated East China Sea , 2013 .

[11]  R. H. Rogers,et al.  Water quality map of Saginaw Bay from computer processing of LANDSAT-2 data , 1976 .

[12]  Yuhai Bao,et al.  Retrieval of sea surface salinity with MERIS and MODIS data in the Bohai Sea , 2013 .

[13]  Palanisamy Shanmugam,et al.  Satellite remote sensing of a low-salinity water plume in the East China Sea , 2008 .

[14]  Simon Yueh,et al.  The Aquarius/SAC-D mission: Designed to meet the salinity remote-sensing challenge , 2008 .

[15]  Yann Kerr,et al.  SMOS: The Challenging Sea Surface Salinity Measurement From Space , 2010, Proceedings of the IEEE.

[16]  N. S. Cooper.  The Effect of Salinity on Tropical Ocean Models , 1988 .

[17]  Cédric H. David,et al.  SMAP observes flooding from land to sea: The Texas event of 2015 , 2016 .

[18]  Kevin E. Kohler,et al.  Influence of precipitation minus evaporation and Bay of Bengal rivers on dynamics, thermodynamics, and mixed layer physics in the upper Indian Ocean , 2001 .

[19]  David Bowers,et al.  Measuring the salinity of the Clyde Sea from remotely sensed ocean colour , 2003 .

[20]  Paul Tett,et al.  Optical Properties of a Region of Freshwater Influence (The Clyde Sea) , 2000 .

[21]  S. Guikema,et al.  Remotely sensed estimates of surface salinity in the Chesapeake Bay: A statistical approach , 2012 .

[22]  Jie Zhang,et al.  Hourly changes in sea surface salinity in coastal waters recorded by Geostationary Ocean Color Imager , 2017 .

[23]  Philippe Richaume,et al.  SMOS Radio Frequency Interference Scenario: Status and Actions Taken to Improve the RFI Environment in the 1400–1427-MHz Passive Band , 2012, IEEE Transactions on Geoscience and Remote Sensing.

[24]  Raymond W. Schmitt,et al.  The global oceanic freshwater cycle : a state-of-the-art quantification , 2010 .

[25]  Gary S. E. Lagerloef,et al.  Satellite mission monitors ocean surface salinity , 2012 .

[26]  Adriano Camps,et al.  A new empirical model of sea surface microwave emissivity for salinity remote sensing , 2004 .

[27]  Christopher Ruf,et al.  Aquarius radiometer RFI detection, mitigation and impact assessment , 2012, 2012 IEEE International Geoscience and Remote Sensing Symposium.

[28]  J. Zedler,et al.  Salinity stress, nitrogen competition, and facilitation: what controls seasonal succession of two opportunistic green macroalgae? , 1996 .

[29]  Matthew D. Grossi,et al.  Satellite-derived coastal ocean and estuarine salinity in the Mid-Atlantic , 2013 .