Interpretation of a backscattering image for the prospecting of Co-rich Manganese Crust

Abstract

The Metal Mining Agency of Japan (MMAJ) had started in operation a multibeam echosounder (HYDROSWEEP) on R/V HAKUREIMARU No. 2 in 1991. The Backscatter Imaging Program was developed in 1992 and started in operation in the next year. The theoretical method program by de Moustier and Alexandrou (1990) or statistical method program for correcting the refractive intensity of each beams are prepared. Ordinary, statistical methods are used to correct whatever has its basis in the mean reflective intensity of each incidence angle. The information derived in the backscatter image is highly significant for MMAJ prospecting the seafloor minerals. The Backscatter Image of Guyot, which exists in the central Pacific, shows the fossil reef structure such as the fringing reef, the inner reef, the sinkhole, and the features of basaltic structure, such as the dome-shaped summit and pinnacles. An abundance of Co-rich manganese crust between seamount tops and upper slopes are related to the presence of outcrops and nodules. Distribution of outcrops estimated from the backscatter image is coordinated to the data of sub-bottom profiling and others. The potential resources of Co-rich manganese crust using the area of outcrops measured with images and expected mean thicknesses of the crust can be estimated by collected samples.