ALBERT

Description: Deep ocean floor is the storehouse of vast quantities of mineral resources and manganese nodules are one of the important resources. The method of semi quantitative evaluation of nodule resource estimation using the rms (root mean square) backscatter amplitude gain values from a multibean echosounding system is presented. Normally, the echosounding system provide information only about the water depths whereas the sidescan images can provide information on the large and small scale roughness and seafloor composition in terms of texture etc. Present day multibeam sonars can produce sidescan images of the surveyed region. The multibeam system- Hydrosweep on Indian Research ship ORV Sagar Kanya doesn't provide the sidescan images, but only gives the rms amplitude values for each of the 59 pre formed beams. In this report, the rms amplitude values are utilised to generate pseudo sidescan images of the seafloor. An area of about 6600 km sup(2) in the Central Indian Basin was mapped using the Hydrosweep system and depth contour and pseudo sidescan images of the area have been generated. A comparison of nodule abundance values with the sidescan image shows that, the light gray patches show high manganese abundance values (more than 10 kg/m sup(2)) where as the dark tones on the sidescan images correspond to low abundance values (up to 4 kg/m sup(2)). As multibeam mapping can be carried out at normal ship speeds, the pseudo sidescan images can be a useful and inexpensive tools for manganese nodule exploration.