Positioning is the most important task in the field of surveying provides an answer to the question; where on earth am I?
There are many instruments available for carrying out positioning, ranging from the old archaic equipment like sextants, theodolites, auto levels etc., to the most modern and latest equipment like total stations, laser scanners and GPS systems.
The level of accuracies of positioning depends upon the objective of the survey and as such, the accuracy levels may vary from few centimeters to few hundreds of meters. For example, surveying and positioning for placement of bridge pier needs accuracy within centimeters; where in a reconnaissance survey for geological mapping, the accuracy needed could be up to few hundreds of meters. Standard Error of Mean can be computed at all instances of time to get the gross error for a particular survey or position to determine the level of accuracy.
Underwater acoustic positioning finds its application in many underwater marine works such as salvage, in oil & gas fields, marine archaeology, tracking of side scan sonar tow fish.

Underwater positioning is more complicated since sound waves do not follow a straight path. Deflection occurs when the sound passes through different thermoclines in the sea. Thermoclines are a result of differences in temperature and salinity. The velocity of sound varies accordingly to these factors, and shadow zones can occur. Therefore it is absolutely imperative to know the variation in the speed of sound throughout the water column for higher positional accuracies. Another problem with sound in water is noise generated from the vessel itself and surrounding objects which can be minimized by meticulous planning.