SUMMARY

For underwater acoustic directionality experiments below 1 kHz, it can be challenging to deploy a sufficiently sized array of hydrophones. The required mounting system could be too large to deploy feasibly in many situations. An inertial vector sensor can act as a solution to this problem. A VS-301 has a nominal frequency range of 10 Hz to 2 kHz, as well as a pressure sensor and a 3-axis accelerometer that measures the particle acceleration of the water near the sensor, which is a directional quantity. This allows for a much smaller mounting system, but it has its own limitations. The vector sensor is sensitive to vibrations from movement and needs extensive calibration to ensure accuracy, as the directionality measurements from the vector sensor are calculated by comparing the amplitude measured on multiple accelerometers. A mounting system with minimal material in the near field was chosen for its ability to minimize acoustic interference, and it was thoroughly tested to ensure it was insulated from non-acoustic vibrations. Two calibration methods were investigated to characterize the VS-301’s sensitivities, such as an acoustic shaker and a standing wave tube device. Both were investigated due to the difference in medium, as one experiment is conducted in air while the other is conducted underwater. With the final mounting system design and confidence in the sensor’s calibration, directionality measurements were taken in a large water tank to ensure that an acoustic source could be located accurately within 5 degrees within a frequency band of 350-1300 Hz.