Abstract:

Deep ocean floor is the storehouse of vast quantities, of mineral resources and manganese nodules are one of the important resources. As these deposits lie at depths greater than 5000 m, sampling the nodules and accurate resource evaluation is expensive and time consuming. Traditional methods of nodule sampling are the free fall grabs and tethered samplers like Vanveen grabs, corers etc, and the remote sensing methods commonly used are deep towed photography and videos. The use of high frequency acoustics for nodule abundance estimation was attempted in the past with partial success. This technique is not conclusive. We present here, method of semi quantitative evaluation of nodule resource, estimation using the rms (root mean square) backscatter amplitude gain values from a multibeam echosounding system. Normally, the echosounding systems provide information only about the water depths whereas the sidescan images can provide information on the large and smart 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. Here in this report the rms amplitude values are utilised to generate pseudo sidescan images of the seafloor. An area of about 6600 km2 in the Central Indian Basin was mapped using the Hydrosweep system and depth contour and pseudo sidescan images of the area have been generated. The area has also been sampled for manganese nodures using the free fan grabs. The pseudo sidescan images provide additional information about the nature of the seafloor. The area surveyed has four seamounts, and the pseudo sidescan image shows light gray tone around these mountains indicating high backscatter amplitude values.

This content is only available via PDF.
You can access this article if you purchase or spend a download.