Early hydrographic surveys consisted of depths measured by sounding pole and hand direct line, with positions based on 3-point sextant fixes to mapped reference factors. Lead strains have been ropes, or traces, with depth markings and direct weights attached. The increase of latest Digital systems – sidescan sonar and multibeam https://messiahremvb.bcbloggers.com/31755704/not-known-details-about-hydrographic-survey-in-bangladesh