HMRG provides data collection, processing and archiving services for towed sidescan and multibeam surveys. Two mapping data archives are currently available on-line at HMRG:
Examples of IMI30 & IMI120 Surveys:
[expand title="2011/2012 Mariana Forearc and Trough"]
The IMI30 was used to map areas in the Southeast Marina Forearc Rifts and the southernmost Mariana Trough Spreading Center during cruise TN273 aboard the University of Washington’s research vessel Thomas G. Thompson, which left Guam on Dec. 12, 2011, and returned on Jan. 22, 2012. This collaborative effort under co-Principal Investigators (PIs) Drs. Fernando Martinez, Katherine Kelley, and Robert Stern was funded by the National Science Foundation (NSF) for field work and subsequent lab study of the tectonic and magmatic evolution of an intraoceanic arc as characterized by the SE Marina Arc rifts (SEMFR) and southernmost Marina Trough spreading center.
the R/V Thompson.
The recent discovery of volcanism in the SEMFR suggests that mantle wedge asthenosphere has been drawn into the rifts. The combined deep-tow sidescan sonar (IMI30) and dredging/wax-coring cruise was designed to determine if the volcanic products recovered by dredging and coring directly reflect variations in slab fluxes and mantle melting associated with varying P-T conditions and breakdown of hydrous minerals in the underlying slab. The regional bathymetric and geophysical data synthesis allows the PIs to kinematically model rift evolution.
Left: Standard HMRG bathymetric and sidescan plots from data collected during TN273. Note that IMI30 sidescan swath widths are greater than the corresponding bathymetric swath widths.
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[expand title="2007/2011 Munitions Surveys in Hawaii"]
Near the end of the second World War large quantities of obsolete, excess and captured munitions, including chemical weapons, were dumped offshore throughout the world’s oceans. In 2007, the Department of Defense (DoD), through its National Defense Center for Energy and Environment, subcontracted the University of Hawaii and a local environmental consulting firm (Environet, Inc.) to conduct the Hawai‘i Undersea Military Munitions Assessment (HUMMA). HUMMA’s objective was to bound and characterize a historic deep-water munitions sea disposal site south of Pearl Harbor to determine the potential impact of the ocean environment on sea disposed munitions and of sea disposed munitions on the ocean environment and those that use it. HUMMA was conceived as the most comprehensive deep-water investigation in the United States to look at both chemical and conventional munitions. Of particular interest for the HUMMA project was historical information indicating that 16,000 M47A2 100-pound (lb) mustard-filled munitions may have been sea disposed south of Pearl Harbor following World War II. To detect and assess DMM, HUMMA participants developed an approach that used innovative technologies to map and sample small targets on the seafloor.
In selecting the system to use for the towed mapping effort, emphasis was placed on balancing the trade-off between resolution and the amount of seafloor that could be mapped based on usable swath width. The IMI120 was ultimately selected because its resolving capabilities would detect 1-2 m objects on the seafloor from average altitudes of 75 m, allowing 2.7 km2 to be mapped per hour. Previous experience searching for wrecks with HMRG’s towed systems revealed that the angle of incidence of sound waves directly affects what a SONAR system can image; therefore, the region around the HUMMA site was surveyed with overlapping tracks in both east-west and north-south directions.
Within the HUMMA Pearl Harbor Study Area, the IMI120 was towed 50-75 m above the seafloor producing a backscatter swath width of 400 m on both the port and starboard sides of the towfish. In the area southwest of Barber’s Point, because the terrain was more undulating, the towfish was towed at altitudes of 75-100 m. The collected IMI120 sidescan sonar data provided the basis for all subsequent investigations. The anomalous small, reflective targets observed in curvilinear trails in the IMI120 backscatter data had the correct size and distribution to make them likely munitions that were cast overboard according to the procedures described in the historical reports from the end of WWII. The final report, figures, and photos detail the IMI120 and other UH systems that were used on the 2007 HUMMA project. The IMI120 was again used for a follow-on HUMMA SONAR Survey in 2011.
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[expand title="2008 Lau Basin IMI120 & Multibeam Data"]In 2008 Dr. Fernando Martinez returned to the Western Pacific aboard the R/V Kilo Moana (KM0804) to continue mapping in the Lau Basin that was begun in 2004 during voyage KM0410. During KM0804 mapping was conducted using both the IMI120 sidescan sonar and the Kilo Moana’s deep-water, 12 kHz-multibeam EM120 sonar. Data from both KM0410 and KM0804 have been submitted to and can be downloaded from the Marine Geophysical Data System; Images from KM0804 include data from both the IMI120 and the EM120 multibeam and are presented here with permission from Dr. Martinez.
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[expand title="2006 Hawaiian Islands Survey"]
In 2006 the IMI30 field program had a short cruise between the islands of Maui and Hawaii to test the engineering improvements implemented earlier that year. The IMI30 performed very well in 2000-2500 mwd, collecting high resolution bathymetry and sidescan on both sides of the sonar. The 3-D perspective belowt shows a comparison of IMI30 bathymetry and the bathymetric compilation dataset under development at SOEST.
Two-dimensional charts of the IMI30 sidescan and bathymetry collected during June 2006 are shown below.
3-D perspective views of the same data are depicted in the below figures. In the 3-D image of bathymetry, contours indicate ten meter depth intervals; the sidescan data are overlain on the same terrain model produced by the bathymetry to allow direct comparison. The subbottom system was operating during this survey, but the area had virtually no sediment cover to image.
Click On The Image Above To See A Larger View
Click On The Image Above To See A Larger View
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[expand title="2004 Lau Basin"]
During its first scientific program in 2004, the IMI30 collected sidescan and bathymetry data for the Lau Basin, but only on the port side of the instrument. Sidescan data agreed well with analogous data collected by the IMI120, and showed far more detail than the data produced by the Kilo Moana’s hull-mounted EM120 (below). Problems resulted mainly from the potted transducers that flooded.
Click On The Image For A Larger View
The IMI30 (left) and the IMI120 (right) were both used on the Lau Basin Survey.
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[expand title="2004 Beaufort Sea Survey"]
In 2005, IMI30 was mobilized on the icebreaker Healy to map the surface and shallow subsurface of the Beaufort Margin, north of Alaska. Unfortunately, ice conditions were too severe to launch the IMI30 except for one fixed station and a four hour survey just north of Barrow, Alaska (the figure above shows the Healy frozen in ice, which lasted for four days of the survey). The first deployment on station (below) was sufficient to demonstrate that the new IMI30 subbottom system was working as expected.
The subbottom data below shows reflectors consistent with those imaged by the Knudsen system that is hull-mounted on Healy.
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