| Popis: |
During a cruise on board the R/V HESPERIDES in October 1996 in the Mediterranean, AVHRR data were continuously obtained on board with a TS300 portable HRPT station. Besides this, near real time SAR data acquired at West Freugh (Scotland) and then downlinked in 3 hours and analyzed by NERSC at Bergen were finally transmitted by Inmarsat to the vessel. The study area Alboran Sea and Algerian basin is characterized by a surface inflow of light Atlantic water that flows along the African coast and became unstable. It develops mesoscale structures (meanders, eddies) that strongly influence the regional circulation and can be tracked by infrared or radar satellite sensors. While AVHRR is an usual tool in oceanography by detecting temperature gradients, SAR can trace current mesoscale structures by their influence on surface roughness. The conceptual model of current shear identification as radar cross-section perturbations developed by NERSC Bergen seems to be promising in the Mediterranean. However, radar backscattering is strongly influenced by the prevailing wind conditions. Meteorological measurements taken on board and TOVS real time data must permit to study the relation between the meteorological conditions and the correlation between ERS-2 SAR and AVHRR SST data. The study was focused in the SAR image of October 6 that clearly delineates the western Alboran gyre. The different characteristics of SAR and AVHRR concerning swath, revisiting time and dependence on atmospheric and in situ conditions resulted in a much higher use of infrared information to guide the in situ sampling that was crucial to track the evolution of the structures to be sampled from the ship, and allowed a maximum efficiency of the available time and resources. At present SAR, although it can better resolve some features, is not yet an operational tool to drive the measuring strategy of an oceanographic ship in latitudes like the Mediterranean Sea. |
