Comparative study between flat and uniform bottom assumptions for snippet imageries in hydrographic applications

Abstract

The length of each snippet data varies with the ensonified area of the beam foot print, which is a function of incidence angle and water depth. Generally, the seabed topology is undulated and it is challenging to determine the exact angle of incident. Therefore the snippet is divided into two operational modes; uniform and flat bottom in order to cope with the complexity of the seabed. However, these assumptions are invalid in real situations most of the time. This study focuses on comparing these two bottom assumption techniques in bottom classification and coverage accuracy using the RESON Seabat 8124 multibeam system at Johor Bahru, Malaysia. Comparative analysis were carried out using hit counts and data gaps interpretation for geometric distortions, intensity profiles and volume comparisons for radiometric distortions in the classified mosaic seabed imagery. Both modes gave a mean difference of 0.54 intensity units on flat seabed areas and 5.97 units on the slope. The data density of the uniform mode is also high. This concludes that one may use either technique for flat areas. But for undulated areas, one has to be careful in selecting the snippet modes, as the real seabed is not completely flat or uniformly sloped.