Investigation of the reliability of satellite imagery for generating shallow water depth information for navigational purposes, Red Sea, Saudi Arabia

Abstract

The Red Sea is considered to be one of the most dangerous seas for navigation. The Saudi territorial waters along the Red Sea are characterised by coral reefs, which cause difficulties for local navigation, especially for coast guard vessels. The responsibilities of the Saudi Border guard necessitate safe navigation through out the entire area including the area of coral reefs; in this thesis a new approach and methods of study have been developed to generate navigational charts from photographic images. Two study areas investigated: Rabigh 150km north of Jeddah and Kishran 200 km south of Jeddah. IKONOS multispectral satellite images acquired specifically for this study with a spatial resolution of 4 meters. The images were processed and geo referenced against control points taken during field measurements. The field work was carried out during the period of acquisition with dGPS being the positioning system (with an accuracy of +-5cm), and depths being measured using HTIOO portable digital echo sounder, purchased specifically for this purpose. After calibration of the satellite images and converting the images from digital numbers to radiance and then finally to reflectance, and after collecting the field depths for both study areas linear regression technique have been employed to build suitable models for extracting the estimated depths, this methodology and process led to successful results with an accuracy reached 97%. The same process employed under the most unfavourable conditions, where the humidity and temperature and water vapour reach the maximum, produced results with an accuracy of 65% are not recommended. Application of the study results were carried out for navigational purposes, by converting the images from raster format to a map containing all the necessary information which is normally available in navigational charts such as depths, contour lines (labeled with depth figures), compasses, scales ... etc. This process was carried out using Geographical Information System (GIS) techniques. As a conclusion the results achieved in this study prove that satellite imagery could play an important part in updating navigational charts by deriving the bathymetry of shallow water areas, especially in areas where the traditional survey could not be undertaken due to the spread of coral reefs, islands and underwater obstacles. - Blue band was found to be the best for penetration and extracting depth data - Timing of acquisition was found to be very important factor for achiving the best accuracy (97.3%)