Sidescan sonar, technology and methods
Sonar data has been an integral method for seabed imaging and bathymetry for decades. Prior to modern AUV implementation, mostly as lay-back towed system from a surface vessel positioned with acoustic transponders. Typical uses are pipeline trench or inspection, seabed imaging for debris or part of a site-survey. In later years new system technology like Synthetic Aperture Sonar (SAS) and Hi resolution Interferometric Synthetic Aperture Sonar (HISAS) has revolutionized both image quality and survey efficiency.
Hi resolution Interferometric Synthetic Aperture Sonar Imaging
Originally, HISAS/SAS was developed for military purposes (UXO, mines and munition etc) MCM operations covering a need to detect and classify even the smallest objects on the seabed in challenging and messy environments, installed in the Hugin AUV. A significant advantage with HISAS is its range independent resolution (RIR), in short 3×3 cm resolution over the full sonar beam range (200m) on each side of the Hugin/Munin vehicle. This efficiency and quality gain equals a minimum coverage of 2 km²/hr at 2kn AUV speed and full coverage sonar and HI-RES SAS bathymetry for accurate 3D object representation.
Theoretical description of the SAS function
The difference between standard side-scan sonar and SAS/HISAS
The above illustration shows the difference between sector scan-sonar, traditionally side-scan sonar and SAS/HISAS
HISAS bathymetry, combining HISAS and EM2040 MBES in HUGIN and MUNIN 1500+
In addition to the HISAS the AUV is equipped with an EM 2040 multibeam echo sounder (MBES), combining the HISAS and MBES results in a coverage for a singular track of more that 20 times the flying altitude above the seabed of the AUV used compared to 3-4 times the altitude using MBES alone.
Source: Kongsberg Maritime Robotics
The above illustration shows the combined coverage swath with for combined HISAS/MBES and MBES stand-alone bathymetry
EdgeTech traditional side-scan acquired by a MUNIN 600 survey. Source: Argeo Survey
HISAS image of data acquired by a HUGIN AUV system Source: Kongsberg Maritime/FFI
