Fig.1

(a) Section of an Envisat SAR image (spatial resolution: 30 m) acquired on 24 July 2011 at 02:44 UTC showing part of the Chinese island of Hainan and the upwelling area off its east coast. Note the curved bright line following the boundary of the upwelling area, which, very likely, is the sea surface signature of an internal solitary wave generated by strong upwelling. (b) Variation of the NRCS along a transect through the SAR image marked by a white arrow. Note that the reduction of the NRCS in the dark area is up to 14dB, which clearly indicates that the reduction is due to the damping of the Bragg waves by surface films."

Fig.2

(a) SST map derived from the MODIS/Acqua data (averaged over 5 days) valid for 24 July 2011 showing a band of cold water along the east coast of Hainan. (b) Chl-a map derived from MODIS/Acqua data (averaged over 5 days) valid for 24 July 2011 showing a band of enhanced Chl-a concentration along the east coast of Hainan. Source: https://podaac-tools.jpl.nasa.gov."

Fig.3

(a) Cyclonic (cold) eddy in the Agulhas Current area off the southeast coast of South Africa (position: 34°S, 32°E) imaged by Sentinel-1A on 16 July 2015 at 0304 UTC. (b) Surface current field as provided by the Globecurrent model. The yellow arrows mark the direction of the surface currents. (c) Sea surface temperature (in ℃) as provided by the Odyssea Regional South Africa model (IREMER)."

Fig.4

(a) Section of an Envisat SAR image acquired on 2 May 2009 at 21:32 UTC showing the upwelling area west of South Africa. The bright line (marked by a solid arrow) denotes the boundary between the upwelling cold area B and the surrounding warmer area A. Also visible is a cyclonic eddy (marked by a broken arrow). (b) SST map of 2 May 2009 showing west of the diagonal line an area of high SST values and east of it an area of lower SST values caused by cold upwelled water (marked by an arrow). (c) Chl-a image of 5 May 2009 showing a band of enhanced Chl-a concentration along the west coast of South Africa and a cyclonic eddy (marked by an arrow). Source: https://podaac-tools.jpl.nasa.gov."

Fig.5

Map showing the location of the Agulhas Current and the Agulhas Return Current. (Red colors denote warm waters and blue colors cold waters)"

Fig.6

(a) Sentinel-1A image acquired on 22 December 2014 at 16:50 UTC in the Extra Wide Swath Mode (swath width: 410km) at HH polarization over the Agulhas Current/Agulhas Return Current area south of South Africa. It shows the sea surface signature of a cyclonic eddy in the Agulhas Return Current having a width of 220km in the center (position: 7.84°S, 26.06°E). (b) Geostrophic surface current streamlines on 22 December 2014 from Globecurrent. (c) SST on 22 December 2014 from the Odyssea Regional Model, South Africa (IFREMER). (d) Chl-a concentration on 22 December 2014 from the Visible Infrared Imaging Radiometer Suite (VIIRS) as provided by NASA."

Fig.7

(a) SAR image acquired by the Chinese GF-3 satellite at VV polarization on 20 September 2018 at 10:03 UTC over sections of the East China Sea and the Strait of Taiwan. It shows dark patches (areas of strongly reduced NRCS values) which,very likely, result from biogenic surface films. (b) Chl-a image of 20 September 2018 derived from MODIS/Acqua data (L3 product, 4km resolution, averaged over 5 days) showing a band of enhanced Chl-a concentration along the southeast coast of Mainland China"