The acoustic position sensing system has been used for the unmanned submersible, however position sensing is affected by environmental factors such as scattering in the sea, ambient noise, thruster noise and others. In this paper the idea of detection probabilty of positions is introduced and its description equation is derived from detection theory and discussed in terms of position measurement, received signal level and sonar noise. The idea is most useful in evaluation of position sensing process and designing position sensing system for the unmanned submersible. The validation of the simulation model of motion and control of the vessel under consideration of position sensing process is examined in comparison with OSR-V system's experiments in the sea, and relationships between detection probability and motion and control of the vessel are examined by its simulation.