Towed Sonar Systems

Originally founded in 1985, HMRG’s early projects were focused on development and deployment of SeaMarc II towed sidescan sonars; 28 SMII expeditions were completed between 1986 and 1991. HMRG engineers have also developed and built a number of towed bathymetric sidescan sonars for in-house use and for customers; three systems are currently available for research and/or commercial contracts. These three sonars, the MR1, IMI30 and the IMI120, share fundamental electronics characteristics, data acquisition computers, and sonar processing software. The different frequencies (12, 30 and 120 kHz) provide a range of capabilities: from mapping broad areas in full ocean depths using a 12-kHz sonar (MR1) that is towed ~100 m below the surface to mapping more restricted areas at much higher resolution using the 120-kHz IMI120 sonar that is towed 50-100 m above the seafloor. The 30-kHz IMI30 provides an intermediate capability with higher resolution than the MR1, but broader coverage than the IMI120.

Having three systems with these shared characteristics results in lower costs for each system, and a larger pool of engineers, technicians and scientists familiar with the maintenance, operations, and data processing requirements of this family of sonars. HMRG can provide full support for sea-going operations, but also trains and incorporates customer-provided personnel in data collection and processing. Because sidescan data are not yet routinely archived at national archives, HMRG maintains on-line, tape and CD/DVD backups of MR1, IMI30, and IMI120 data at SOEST.

HMRG’s Family of Towed Sonar Systems:  HMRG currently maintains and operates three towed bathymetric sidescan sonar systems that provide a wide range of mapping capabilities:  MR1, IMI120, and IMI30.  Additional oceanographic sensors, including magnetometers, subbottom profilers, motion sensors, sound velocity profilers, and CTDS, are or can be deployed as part of the instrument packages.

MR1: The MR1 is a shallow-towed 11/12-kHz bathymetric sidescan sonar developed and operated by HMRG.  The MR1 provides full ocean depth capabilities, both bathymetry and sidescan data, and broad coverage and has been deployed on over 30 cruises since 1990.

IMI120: The IMI120 is a deep-towed 120-kHz bathymetric sidescan sonar originally developed by Woods Hole Oceanographic Institute as the DSL-120, subsequently rebuilt as the DSL-120A with an HMRG-engineered mapping sonar, and jointly operated by WHOI and HMRG for several years.  Now named IMI120 (IMI means “Seeker” in Hawaiian) and operated by HMRG, this instrument provides high-resolution sidescan and phase-difference bathymetry for detailed analysis of seafloor features and is towed 50-100 m above the seafloor.

IMI30:  The IMI30 is a 30-kHz bathymetric sidescan sonar developed and operated by HMRG.  At 30 kHz, IMI30 produces higher resolution data than the MR1, but broader coverage than the IMI120 and is towed several hundred meters above the seafloor.