Precision and bias in estimating detection distances for beaked whale echolocation clicks using a two-element...

Area of Science:

• Marine bioacoustics
• Cetacean research
• Acoustic signal processing

Background:

• Accurate detection distances are crucial for estimating cetacean density and abundance using distance sampling.
• Beaked whales are difficult to study due to their elusive nature and deep-diving behavior.

Purpose of the Study:

• To evaluate methods for estimating horizontal distance (range) to beaked whales using echolocation clicks.
• To assess the impact of array geometry, tilt, and depth on range estimation precision.

Main Methods:

• Utilized a drifting buoy system with a two-element vertical hydrophone array.
• Employed time-difference-of-arrival (TDOA) estimation for direct and surface-reflected clicks.
• Applied a Teager-Kaiser energy detector to enhance TDOA estimates for surface-reflected signals.
• Conducted simulations to analyze the influence of array tilt and depth on range estimation.

Main Results:

• Range estimation was unreliable with the tested array geometry and TDOA error.
• Reducing array tilt to <0.5° enabled reliable range estimation up to ~3000m.
• Increasing array depth to 200m and maintaining tilt <1° extended reliable range estimation to ~5000m.

Conclusions:

• Array tilt and depth significantly impact the reliability of beaked whale range estimation.
• Prior information on whale depth and declination angle can improve range precision but requires specific analytical approaches.
• Optimizing hydrophone array configuration is key for accurate distance sampling in cetacean research.