Near Shore Bathymetry Evaluation using Remote Sensing Method
Ekpa, A. U. and Ojinnaka, O. C.
Journal Title:Journal of Environmental Issues and Agriculture in Developing Countries
This study explores the application of satellite remote sensing technique in nearshore bathymetry. The study area is a section of Cross River which lies between Akwa Ibom State and Cross River State, as well as Bakassi Peninsula. The extensive coastal waters of Nigeria have remained uncharted due to constraints imposed by government policy, funds and technological limitations. The applications of conventional technique of bathymetry such as echo sounders or swath sounding systems are inadequate for mapping very shallow areas due to sensor fouling or prohibitive cost in attempt for full sea floor coverage. The data employed include multispectral Landsat-7 ETM+ image set of year 2000, sounded depth for 2012, tidal data and extract from Admiralty tide tables. Tidal prediction was carried out for 2012 and in retrospect for 2000. The sounded data and Landsat-derived depth were reduced to the same Chart datum for ease of evaluation. Atmospheric correction of the satellite image was accomplished using Improved Image-Based Dark Object Subtraction (DOS) Model, while Stumpf’s Ratio Model was employed to estimate the bathymetric depths. The depths derived from the ratio of blue/red bands reveal better bathymetric depths than the ratio of the blue/green bands when compared with the sounded/ground truth data. The results obtained agree with the specifications for under-keel clearance in shallow water navigation and therefore showed that this technique can be adopted for safe mapping of the Nigerian Coastal waters. This is an efficient and cost-effective technique for near shore bathymetry and is therefore strongly recommended for mapping and monitoring of sea floor changes in our coastal waters.