Controlling noise to improve underwater positioning

Remotely operated vehicles (ROVs) are vital to the performance of many underwater tasks. They need to be precisely positioned over considerable areas in water that precludes the reliance on optical sensors alone. Acoustic positioning has the advantage of low attenuation through the water (<10 dB/km in a 18-36 kHz bandwidth). This widely used frequency band gives operational ranges of several km, and precise positioning to 0.1 m. Any acoustic system is vulnerable to excess noise, and the trend towards ever more powerful work class ROVs has led to increased noise levels. System designers naturally need to know the likely operating ranges of the positioning equipment being supplied, but find there is little noise data available. The author looks at how noise levels can be measured to provide these predictions for several different systems