Observing river deltas
4 April 2016 08:40 UTC, 08:45 UTC and 09:12 UTC
Observation of the deltas of the Danube and Nile rivers in April 2016.
05 September 2023
04 April 2016
By Jose Prieto (EUMETSAT) and Jakub Walawender (IMGW-PIB)
New composites from SEVIRI channels, based on enhancement of solar and infrared window composites, help to monitor sediments transported by the rivers and deposited at deltas.
The products show the suspended matter which is discharged by the rivers into the sea, helping to extend the estuaries in the geological time scale.
The turbid waters can be identified even at the Meteosat pixel resolution of 4km.
Solar comparison
Figure 1: Generally, enhancing a differences’ solar composite around standard values for sea pixels helps highlight the clear areas with more or less waves and wind. Stronger breezes appear as green and calm waters appear as yellow.
In Figure 1 the solar channel difference composite (right) shows the special soil of estuaries formed by sediment deposition (black patches) which cannot be seen in SEVIRI Natural Colour RGB (left), although they can be identified in MODIS True Color images at 250m resolution (Figures 2/3).
View the KMZ file of solar difference composite image in Google Earth.
The same composites offer, in the broader scale, indications on the surface conditions due to the wind (solar composite), sea temperatures, and humidity in the boundary layer (infrared composite).
On the solar composite red is the difference between 1.6µm–0. µm, green is 0.8µm–0.6µm and blue is 0.6µm. The image has been enhanced to mark the difference between the delta soil and soil from surrounding regions, with higher albedos at the 1.6µm and 0.8µm channels, but similar values at 0.6µm.
Infrared comparison
Figure 4: The enhanced infrared images over the Mediterranean give an indication on humidity areas (NW of Nile delta) compared with dry air (N/NE of Nile delta). The channel 10.8µm informs on surface temperature in the absence of cloud.
The infrared difference image (Figure 4, left) shows a different picture from the solar difference composite (Figure 1, right). The former informs on humidity in the low atmosphere, the latter on the surface roughness. The wind physically connects the two images, since it cools the surface temperature and increases the humidity above the surface.
By focusing on typical values for the sea pixels, values over land usually saturate the differences and appear uniform in the display. This is not useful for land analysis, but displays a wealth of data not present in the usual natural rendering.
