The filtering and compressing of outer beams to multibeam bathymetric data
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ORIGINAL RESEARCH PAPER
The filtering and compressing of outer beams to multibeam bathymetric data Fanlin Yang • Jiabiao Li Litao Han • Zhimin Liu
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Received: 22 July 2012 / Accepted: 8 November 2012 / Published online: 17 November 2012 Ó Springer Science+Business Media Dordrecht 2012
Abstract Some errors and noises are often present in multibeam swath bathymetric data. Echo detection error (EDE) is one of the main errors. It causes the depth error to become bigger in outer beams and looks like sound refraction. But depth errors due to EDEs have a trumpetshaped appearance, instead of a curved appearance that is caused by the sound refraction errors. EDEs, including systematic acoustic signal detection errors and internal noises, cannot be removed during the correction of sound refraction. It causes depth inconsistencies between adjacent swaths and degrades precision of outer beams. Sometimes, the bathymetric errors caused by EDEs do not even meet the requirements of IHO (International Hydrographic Organization). Therefore, a post-processing method is presented to minimize the EDEs by filtering outliers and compressing outer beams of multibeam bathymetric data. The outliers caused by internal noises are removed by an automatic filter algorithm first. Then the outer beams are compressed to reduce systematic acoustic signal detection errors according to their depths, the calculated depth line and standard deviations (SDs). The automatic filter process is important for calculating the depth line. The selection of inner beams to calculate the average SD of beam depths is
F. Yang (&) L. Han Z. Liu Geomatics College, Shandong University of Science and Technology, Qingdao 266590, China e-mail: [email protected] F. Yang L. Han Key Laboratory of Surveying and Mapping Technology on Island and Reef, NASG, Qingdao 266590, China J. Li Key Laboratory of Submarine Geosciences of State Oceanic Administration, Hangzhou 310012, China
crucial to achieving compressing goals. The quality of final bathymetric data in outer beams can be improved by these steps. The method is verified by a field test. Keywords Multibeam echosounder system Echo detection error Outer beam
Introduction Modern multibeam echosounder systems (MBES) can provide high resolution seafloor terrain, backscatter and water column images (Clarke 2006). The technology has revolutionized the practice of hydrography and has improved the accuracy of and confidence in hydrographic charts. It has a wide range of applications in ocean engineering, seafloor deformation monitoring, ocean military, etc. Therefore, as ocean development speeds up, developing a high-precision multibeam bathymetry technique is one of the major marine survey research topics. However, the bathymetric data of MBES can be contaminated by a variety of sources of horizontal and vertical errors since MBES integrates several sensors and its acoustic signal travels via sea water. Horizontal errors of MBES can be well controlled with modern GNSS (Global Navigation Satellite System) technology (Colom
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