Satellite data for local investigation in coastal zones: case study for Tangier area (Morrocco)

Recent operative satellite multispectral sensors like MERIS, MODIS with more traditional AVHRR and SeaWiFS and high resolution ASTER and ASAR give an unique opportunity for investigation of the marine processes with spatial scale from few hundred meters and temporal variability from few hours. In addition to this, QuikScat wind data helps to better understand an eventual forcing variation. One of the most important processes in coastal area is water (and probable pollutants) transport and mixing. Optical and thermal properties of the water or surface roughness peculiarities can be used as tracers or markers on subsequent images for the estimation of the currents structure and pollution displacement in ocean upper layer. Such kind of investigation is subject to significant interest near the ports and cities surroundings due to strong anthropogenic impact. Processes for the Tangier bay area were investigated by the means of the above-mentioned satellite data coupled with CTD and ADCP field measurements (August 2003). This analysis shown the strong influence of the mesoscale processes like eddies and wind driven upwelling on the currents patterns in the coastal zone. On the basis of the ASTER and ASAR data we estimated typical pollutions pathways. MODIS (Aqua and Terra ) and MERIS data were used for investigation of the variations of the water optical properties on time scale from few hours. This scale is important according to the typical 12 hours tidal motions in Tangier bay area Mutual analyses shown that mixing on Camarinal sill play a significant role in exchange processes in Tangier bay . AVHRR SST data set were analyzed together with QuikScat wind data. This analysis shown that Westward winds caused coastal upwelling phenomena with temperature difference up to 10° C. Quikscat spatial wind variability was also compared with NCEP wind data in nearest point --6W, 36N. Animations for different seasons, on the basis of subsequent thermal AVHRR images, highlighted the variability of regional dynamics. In addition, SeaWiFS time series images were processed, analyzed and compared with MODIS and MERIS data. Multispectral and multisensors approach for Tangier coastal areas study shown high efficiency at that scale, and can obviously be used for other regions

Recent state of the Aral sea from regular satellite observations. 35th COSPAR Scientific Assembly

The Aral Sea disaster is one of the most significant examples of ecological catastrophe caused by mismanagement of water resources. Aral sea level dropped on 22 meters for the last 35 years. The sea separated in to two independent parts , the Large Sea(Southern) and the Small Sea (Northern), loosing more than 90% of its original water masses. After the collapse of the former Soviet Union, satellite retrieved data became the main source of information on this perishing system. Regular observations from AVHRR, SeaWiFS, MODIS and ASTER satellite sensors were used for our investigations. Sea surface temperature (SST) data of the AVHRR sensor and digital bottom map topography were used for sea level drop calculations. The Sea level defined as the digital map isobate corresponds quite well to the satellite derived coastline for the Eastern part of the Large Sea with a bottom slope of ˜ 0.00015. For the period 1989-2002 the sea level of the Large Sea dropped on 9.2 meters. However in 2003 the sea level remained stable. This stabilisation was due to an increase of water output of the rivers Amu--Darya and Syr-Darya in 2003. High resolution ASTER data showed that the main amount of Syr-Darya waters is discharged into the Large Sea. The dried bottom area now covers more than 45000 km2. On the base of AVHRR-SST data the temperature regime for different parts of the Aral Sea was calculated for the years 2002-2003. The annual amplitude of the SST variation reaches 37° C for the open waters. The observed minimum freezing point was -7° C due to very high salinity. Estimations from satellite retrieved freezing points show an increase of salinity up to 10% in the Eastern part of the Large Sea. It is almost paradox that on satellite images the ice appears warmer than the water. Strong variations of the water temperature (up to 5° C) within a few days could be observed from April to August and could be related to wind induced mixing. SeaWiFS ocean colour data were used for the investigation of the optical properties of the water in different parts of the Aral Sea for the years 2002-2003. A significant relation of optical properties with wind and temperature was obtained. Strong changes of the thermal regimes of the Sea can cause variations in local climatic conditions: The analysis of AVHRR NDVI - data for the surrounding areas demonstrated a shift in the annual vegetation cycle. In addition phenomena like: salt storms, wind driven tides, sources of groundwater, eddies and frontal structures as well as ice coverage of the Aral Sea were demonstrated on satellite images