Some Considerations about Image Analysis of Seafloor Photographs for Better Estimation of Parameters of Polymetallic Nodule Distribution

For continuously-taken seafloor photographs of polymetallic nodule, automatic procedures of image processing and subsequent treatment of a vast amount of data have been developed for estimating parameters representing distribution of polymetallic nodules such as sizes, numbers, coverage and abundance of nodules. The authors discussed about the related topics, based on digital photographic data obtained from survey cruises conducted in Japanese license area in Clarion-Clipperton Fracture Zone. First, the authors calculated systematic errors of estimation which can be caused by miss-setting of the threshold values used in the automatic extraction of polymetallic nodules. Second, the degree of the heterogeneity of nodule distribution was estimated quantitatively by differences of statistical characteristics between adjacent seafloor photographs. Since strategies of the procedures such as segregation of connected nodules or distinction between nodule and other materials can also cause systematic difference of the estimation, the strategies should be explicitly pronounced for compilation of photographs and analyzed data with different backgrounds.