Optical remote sensing of turbidity and total suspended matter in the Gulf of Gabes
Optical remote sensing was used to provide scientific information to support environmental management in the Gulf of Gabes that is located in the southeastern coast of Tunisia. This region is characterized by shallow continental shelf subjected to semi-diurnal tides. Industrial activities in this area since the early 1970s may have contributed to the degradation of the biodiversity of the ecosystem with eutrophication problems and disappearance of benthic and planktonic species. To assess the long-term effect of anthropogenic and natural discharges on the Gulf of Gabes, the optical environment of the coastal waters is assessed from in situ measurements of total suspended matter concentration (TSM), Secchi depth and turbidity (TU). This monitoring requires regular seaborne measurements (monthly), which is very expensive and difficult to obtain. The objective of the present study is the evaluation of the Moderate Resolution Imaging Spectrometer (MODIS) AQUA data compared with two sampling campaigns realized at the study area. To map turbidity data from MODIS images, a semi-empirical algorithm was applied at band 667 nm. This bio-optical algorithm has already been calibrated and validated on the Belgian coast. The validation of this algorithm on the Gulf of Gabes using in situ measurements of turbidity and remotely sensed turbidity obtained from MODIS imagery shows a correlation coefficient of 68.9%. Seasonal and annual average maps for TSM and TU were then computed over the Gulf of Gabes using MODIS imagery. The obtained results of TSM and TU from remotely sensed data are conformable with those obtained through the analysis of in situ measurements. Therefore, remote sensing techniques offer a better and efficient tool for mapping and monitoring turbidity over the whole region.
KeywordsRemote sensing Turbidity Total suspended matter Gulf of Gabes
This study was funded by the Unit of Structure and Geologic Model of University of Sciences of Tunisia. Thanks are extended to the Tunisian Chemical Group GCT for their assistance in collecting the in situ measurement in the Gulf of Gabes. The NASA ocean colors product distribution teams at The Goddard Space Flight Center GSFC are acknowledged for the distribution of MODIS products. This study was carried out in collaboration with the BELCOLOUR-2 project funded by the Belgian Science Policy Office STERO program.
- Babin M, Stramski D, Ferrari GM, Claustre H, Bricaud A, Obolenski G (2003) Variations in the light absorption coefficients of phytoplankton, non-algal particles, and dissolved organic matter in coastal waters around Europe. J Geophys Res 108. doi: 10.1029/2001JC000882
- Ben Mustapha K, Hattour A, Mhetli M, El Abed A, Tritar B (1999) Bionomie des étages Infra et Circalittoral du golfe de Gabes. Bull Inst Natn Sci Tech Mer (Tunisie) 26(2):5–48 (French bibliographie)Google Scholar
- Bjaoui B, Rais S, Koutitonsky V (2004) Modélisation de la dispersion du phosphogypse dans le golfe de Gabes. Bull Inst Natn Scienc Tech Mer (Tunisie) 31:103–109, French bibliographieGoogle Scholar
- Burollet PF, Clairefond P, Winnock E (1979) La mer Pélagienne (étude sédimentologique et écologique du plateau tunisien et du golfe de Gabes). Géol Méditerranéenne Ann Univ Provence 6(1):1–345, + cartes, (French bibliographie)Google Scholar
- Nechad B, Ruddick KG, Neukermans G (2009) Calibration and validation of a generic multisensor algorithm for mapping of turbidity in coastal waters. Proceedings of SPIE “Remote Sensing of the Ocean, Sea Ice, and Large Water Regions” Conference held in Berlin (Germany), 31 August 2009. Proc. of SPIE 7473: 74730H. doi: 10.1117/12.830700.
- Sogreah (2002) Protection des ressources marines et côtières du Golfe de Gabes, Sogreah, Tunisie phase préparatoire du projet GEF/WB TF 022968. Rapport de phase 1: Diagnostic, 229 pp (French bibliographie)Google Scholar
- Tilstone G, Moore G (eds) (2002) REVAMP Regional Validation of MERIS Chlorophyll products in North Sea coastal waters: protocols documentGoogle Scholar
- Wass PD, Marks SD, Finch JW, Leeks GJ, Ingram JK (1997) Monitoring and preliminary interpretation of in-river turbidity and remote sensed imagery for suspended sediment transport studies in the Humber catchment. Sci Total Environ 194–195:263–283. doi: 10.1016/S0048-9697(96)05370-3 CrossRefGoogle Scholar