Field Calibration Procedures for Multibeam Sonar Systems

摘要

Multibeam sonar systems are the latest advancement in hydrographic surveying technology. These systems consist of a transducer, motion sensor, gyrocompass, and navigation system. Reliable data can only be acquired after proper calibration has been performed on the system as a whole. This calibration begins with the alignment and static offsets of the sensors referenced to the centerline of the vessel and the transducer. The alignment will reduce the static corrections of each sensor and can be performed with either GPS receivers or a total station geodetic instrument. After the static offsets are determined, a patch test is performed. This test is designed to reveal the following residual biases: (1) pitch offset, (2) roll offset, (3) positioning time delay, and (4) azimuthal offset. The test consists of a small survey of several lines that are evaluated for inconsistencies and then corrected using software designed for multibeam surveys. There are several mathematical equations developed for analyzing these biases that are incorporated into the processing software for the patch test. The performance test is the final check of the offsets and biases to verify whether the data meet accuracy requirements for the survey. This test is a series of parallel and cross lines with significant overlap to give redundant data.