Near-field beamforming for a Multi-Beam Echo Sounder: Approximation and error analysis

For a Multi-Beam Echo Sounder (MBES) operating in very shallow water environments or close to seafloor, near-field beamforming shall be used to estimate the direction and range of the backscattering sources along the bottom. The most common beamforming method is the so-called weight-delay-sum (WDS) beamformer. In this paper, we present an approximation method to calculate time delays between individual array elements that can be applied to an arbitrarily-shaped array operated in near-field conditions. The result is applied to a practical MBES configuration with a curved receiving array. Phase-shift error analysis and comparison between the accurate beam patterns and the approximate beam patterns are implemented, and the results demonstrate that the developed method is quite efficient in computation while being enough accurate.