Underwater localisation correction method for drifting anchor nodes with an extra floating anchor node

Drifting of anchor nodes due to ocean currents and tides is a challenging issue in efficient localisation for underwater acoustic sensor networks. This study therefore proposes a correction method to compensate the error caused by drifting (and accurately localise the target) by introducing an extra floating anchor node. The floating anchor node is placed in the middle of the localisation area and its coordinates are known by GPS. The floating anchor node acts as a reference node and therefore is useful in compensating the localisation error. The detailed method consists of three stages: (i) estimate the floating anchor node's location with other anchor nodes; (ii) calculate the compensation parameter from both real-time and calculated coordinates of floating anchor node; and (iii) locate the target with anchor nodes first and then correct the result with compensation parameter calculated in stage (ii). Simulations and experiment results show that the proposed method produces a improvement in localisation accuracy. A remarkable improvement of 27% is demonstrated with the experimental data with the cost of only a single floating anchor node.