Maximum likelihood estimators and Cramér-Rao bound for estimating azimuth and elevation angles using compact arrays.

Area of Science:

• Acoustics
• Signal Processing
• Oceanography

Background:

• Accurate sound source localization is crucial for underwater applications.
• Compact hydrophone arrays offer a viable solution for acoustic sensing.
• Estimating azimuth and elevation angles precisely remains a challenge.

Purpose of the Study:

• To develop and evaluate closed-form estimators for sound source azimuth and elevation using time-difference of arrival (TDOA).
• To assess the accuracy of these TDOA-based estimators through simulations and in situ testing.

Main Methods:

• Derivation of closed-form solutions for TDOA-based angle estimation algorithms.
• Statistical simulations to evaluate estimator performance against theoretical bounds.
• In situ experiments using hydrophone arrays in real-world underwater environments.

Main Results:

• TDOA-based estimators achieve accuracy close to the Cramér-Rao lower bound in simulations.
• Refraction, reflections, and complex sound propagation significantly increase angle estimation errors in situ.
• Identified unpredictable sound propagation effects as primary sources of large, slowly varying errors.

Conclusions:

• Closed-form TDOA estimators provide a strong foundation for underwater acoustic source localization.
• Environmental factors like refraction and multipath propagation are critical limitations for real-world performance.
• Further research is needed to mitigate errors caused by complex underwater sound propagation.