Bishwajit Chakraborty

Acoustic Characterization of Seafloor Sediment Employing a Hybrid Method of Neural Network Architecture and Fuzzy Algorithm

Seafloor sediment is characterized acoustically in the western continental shelf of India using the echo features extracted from normal incidence single-beam echo sounder backscatter returns at 33 and 210 kHz. The seafloor sediment characterization mainly depends on two important parameters: the number of sediment classes prevailing in the area and the selection of features having most prominent discriminating characteristics. In this letter, a method is proposed using Kohonens self-organizing map to estimate the maximum possible number of classes present in a given data set, where no a priori knowledge on sediment classes is available. Applicability of this method at any site is illustrated with simulated data. In addition, another method is proposed to select the three most discriminating echo features using a fuzzy algorithm. The comparison of the results with ground truth at two operating frequencies revealed that this hybrid method could be efficiently used for sediment classification, without any a priori information and applicable for a wide range of frequencies.

Multifractal Detrended Fluctuation Analysis to Compare Coral Bank and Seafloor Seepage Area-Related Characterization Along the Central Western Continental Margin of India

In this letter, the characterization of two coral banks is initiated employing the multifractal detrended fluctuation analysis (MFDFA) for multibeam bathymetry and associated backscatter data. The seafloor roughness was estimated using the Hurst exponent of a second-order moment. The two coral banks are located around the buried channels off Malpe, western continental margin of India (WCMI). The Gaveshani bank is lying on a submerged headland with high backscatter strength. The presence of greater seafloor roughness and medium multifractality in the backscatter data series indicates less heterogeneity of the involved process. In an evolutionary process, the Gaveshani bank may not be affected by the paleochannels. Contrary to the Gaveshani bank, another unnamed coral bank located on lowland and with lower backscatter strength shows lower seafloor roughness and greater multifractality, comparatively. This smoothness is due to the considerable heterogeneity of the seafloor process of a paleochannel system. During the Holocene period, the waves and the current action have further modified the morphology of the coral banks. To support the present analysis, we have juxtaposed the multifractal data analysis of seepage and nonseepage seafloor off Goa, WCMI, along with the coral banks.