Detecting horizontal gradient of sound speed in ocean

We propose a new approach to monitor the horizontal gradient of sound speed in ocean for its correction on seafloor positioning using the GPS/ acoustic technique. The new method requires five seafloor transponders to solve five parameters: δx, horizontal position of a transponder array; δt, a common delay in traveltimes due to the stratified component of sound speed; V_t, the gradient of traveltime delays among the transponders associated with the sound speed gradient. We also numerically evaluate the geometrical tsength of the five transponders' layout and observation point to avoid possible trade-off among the parameters.