Tunnel effect elimination in multi-beam bathymetry sonar based on apFFT algorithm

Analyzed the tunnel effect and its mechanism of appearance in multi-beam bathymetry sonar and pointed out that the side lobe interference was an important factor which caused the tunnel effect, and the existence of tunnel effect would lead to the multi-beam bathymetry sonar mistake relatively flat seafloor for concave-up horizontal half cylinder terrain. Studied on all phase FFT (apFFT) algorithm and analyzed its immunity to side lobe interference with theoretic deduction and computer simulation, and used the algorithm to process the tunnel effect existed in the lake experiment data. The processing results proved its validity in eliminating the side lobe interference in edge beams of multi-beam bathymétrie data.