Seafloor mapping of large areas using multibeam system - Indian experience

Abstract

To identify unproductive and difficult terrains, a detailed picture of the seafloor was essential. Hence, the area was resurveyed using the multibeam system hydrosweep during 1990-93. A total of 300,000 sq.km area has been mapped. As the average depth in the basin is about 5100 m a line spacing 5 nm ensured 100% coverage of the entire area. Over 31 nm million depth data points were collected from the multibeam sonar system in the CIB. By developing new software, data from different lines were averaged and merged to produce large area maps. Maps were generated in the scale of 1 mil. and 1.5 mil covering area of about 2 mil. sq.km in single map. Also, depth contour interval were generated. A computer program was developed to convert the depth data grid into slope angle grid and slope angle maps of the area were also prepared. Numerous prominent seamount and abyssal hills (total of about 157) were identified from the survey. Clear topographic signature for southern extension of the 79 degrees E fracture zone was also obtained. Generally, it was observed that the northern part of the basin (10 degrees -12 degrees 30'S) was plain while the southern part of the basin (12 degrees 30' to 15 degrees S) was rugged