sentences:  Because these devices sent out broad-beam sound waves from the sea surface, details of the sea floor shape remained obscured by fuzzy smeared out echoes.Ship navigation was so inaccurate that features smaller than a few kilometers across could not be mapped with any certainty.Spiess’ solution to the resolution and mapping problem was twofold; bring the echo sounder close to the sea floor and locate the device within a seabed survey network.