Internal Solitary Wave(ISW) Propagation Characteristics Research In The Northern South China Sea(SCS) Based On Multisatellite Observations

Internal solitary waves(ISWs) occur ubiquitously in China’s waters: the South China Sea(SCS). ISWs have long attracted much research interest because of their important role in ocean acoustics, offshore engineering, ocean mixing, primary productivity, and submarine navigation. ISWs have sea surface signatures that can be detected by satellite synthetic aperture radar(SAR) and optical sensors. Satellite remote-sensing images provide excellent two-dimensional views of the ISW field. Our understanding of ISWs in the SCS has been greatly improved using satellite remote-sensing techniques.The first primary objectives of this paper are to review the development of remote-sensing techniques in the study of ISWs and to summarize ISW characteristics in the SCS, mainly demonstrated by remote-sensing techniques. In addition, several issues with remote-sensing techniques and interesting research topics are discussed.In the first Chapter, internal solitary waves(ISWs) are observed 2 times within 30 min in synthetic aperture radar(SAR) image pairs from the Envisat and ERS-2 tandem satellites. Three pairs of SAR images were acquired in the South China Sea(SCS) in April 2007, August 2008, and March 2009, and 13 ISWs were tracked between the image pair in an Arc GIS environment. The phase speeds of these ISWs are calculated from their spatial displacement and time interval. The resultant ISW speeds agree well with the theoretical values estimated from the SturmLouisville equation using local bathymetric and monthly climatology ocean stratification data. This technique reveals the spatial variation in the ISWs speed in the water depth between 100 and 4000 m in the SCS. The study shows that ISWs speed is mainly affected by bottom topography and generally decreases from deep to shallow water from east to west and from south to north.In the second Chapter, the propagation of internal solitary waves(ISWs) in the South China Sea(SCS) was tracked using National Aeronautics and Space Administration(NASA) Moderate Resolution Imaging Spectroradiometer(MODIS) and the Visible Infrared Imaging Radiometer Suite(VIIRS) sun glint image pairs. The acquisition times of the two images comprising thesame pair is usually separated by about 2 hours. Four pairs of images in May and August 2013 were analysed. The ISW phase speeds were derived using the horizontal displacement of the ISW patterns and the time difference between the 2 satellite images. The phase speeds were in good agreement with the theoretical calculations using the Sturm–Louisville(S- L) equation with a non-linear term. Monthly ocean stratification data and bathymetry were used in the theoretical calculations. The ISW phase speeds are mainly affected by bottom depth, with seasonal variations. The ISWs propagated faster in August than in May. Our results also show that the ISW propagation in northern SCS can be mapped using environmental satellite sun glint images in short period of time with the advantage of large scale.In the third part deals with the co-registration of multi-satellite images from ENVISAT ASAR and Terra MODIS sensors, 96 derived ISWs from the eleven collected pairs of SAR/ MODIS images in the north SCS and then estimated ISW speeds from these satellite images, compared with theoretical values derived by solving T-G equation. Also extracting the mixed layer depth from the northern SCS and then mapping the water depth and ocean stratification. Preliminary study the on ocean stratification ISW phase speed variation. The phase speed increase in proportion to the ocean mixed layer depth increase in the northern SCS.