Abstract:

An improved survey method for estimating the geodetic position of acoustic sensors placed at fixed but unknown locations on the seafloor is developed. Bottom-mounted sensors are surveyed using an extension of the classic trilateration terrestrial survey technique, i.e., making ranging measurements from reference points to the point to be surveyed. For acoustic sensors, these ranging measurements are obtained by transmitting an acoustic signal from a near surface projector and making corresponding timing and/or position measurements. Historically, sensors have been surveyed either relatively or geodeticly. A crucial calculation required for both cases is the effective sound speed (ESP). To avoid systematic (nonrandom) errors in the ESP calculation, an unbiased measurement for the sound speed profile (SSP) is a prerequisite. However, a typical measured SSP may have a 2-m/s bias error. Consequently, the traditional methods may suffer significant errors on estimating the sensor coordinates. The newly developed method considers the timing and sound speed biases, in addition to the sensor coordinates, as parameters to be estimated. In modeling this way, the bias errors are precluded from propagating to the sensor coordinates. Results with both simulated and actual field data show that this new method has significant improvement over traditional methods.