Simplified calibration method for multibeam footprint displacements due to non-concentric arrays

Abstract When the offset between the transmitter and the receiver in the multibeam is large, neglecting the offset will introduce depth errors into the multibeam footprints. Although the current non-concentric algorithm (NCCA) considers this offset, its model is complicated and time-consuming. To solve the issues, a simplified method is developed. First, the offset is considered by constructing two separated intersecting triangles projected by the transmitted and received cones under the array reference frame (ARF); second, two groups of the footprint coordinates under the ARF are calculated with slant ranges from the transmitter and receiver to the footprint, respectively; then, the transmitted and received vectors, and their corresponding one-way travel times (OWTTs) are calculated by the two coordinates; finally, an iteration is used to adjust the two slant ranges according to the measured and the calculated time, and the optimal location of the footprint will be obtained. To verify the proposed method, comparisons between existing methods and ours are made. The results indicate that when the depth is about 457 m, the average depth deviation between the NCCA and ours is only 0.03 m. And our new method saves about 17% of computation time compared to that of the NCCA.