HAWAIIMR1 Swath Mapping and Underway Geophysics Acquisition and Processing

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HAWAII-MR1 Swath Mapping and Underway Geophysics
Acquisition and Processing

• Andrew M. Goodliffe
• Department of Geological Sciences
• University of Alabama

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• The HAWAII-MR1 (Hawaii Wide-Angle Acoustic
  Imaging Instrument) is a towed interferometric
  swath mapping system.
• Both sidescan and bathymetry data are produced

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• The system is deployed from a specially designed
  LRS (launch and recovery system).
• It is towed behind a depressor weight which is in
  turn attached to the LRS.
• This configuration decouples the system from the
  ships motion.
• The system is towed beneath the mixed layer
  (60-100 m)
• Once deployed, the system can be operated in up
  to sea state 6, conditions that would cause the
  serious degradation of conventional hull mounted
  mapping systems.

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• In a conventional sidescan system a single
  transducer array measures traveltime after the
  transmission of a signal.
• In the HAWAII-MR1 system two arrays are arranged
  in parallel
• The phase difference between the same signal
  received at each array indicates the angle from
  which that signal came.
• This permits the calculation of depth in addition
  to traveltime and amplitude.
• Pairs of arrays are mounted on each side of the
  system. The port pair operates at 11 kHz, and the
  starboard pair at 12 kHz
• Bathymetry swath width is in excess of 3.4 times
  water depth.
• Sidescan swath width is in excess of 7.5 times
  water depth.

Courtesy of Mark Rognstad, University of Hawaii.
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• The bathymetry and sidescan data are fully
  processed at sea.
• Real time images of bathymetry and sidescan are
  displayed
• The raw data is redundantly archived to dual tape
  drives.
• Sidescan processing includes several amplitude
  normalization, destriping and despeckling
  routines.
• The Unix/Linux based sidescan and bathymetry
  software is freely available from the HawaiI
  Mapping Research Group (HMRG).
• All willing shipboard scientists are fully
  trained in the use of the HMRG software.

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The examples on the left show bathymetry (top)
and sidescan (bottom) from the Woodlark Basin,
Papua New Guinea. In this basin wide survey the
location of the spreading center is clearly
visible as a dark band along the center of the
basin. Basin bounding faults are also clearly
visible.
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• The R/V Maurice Ewing routinely collects
• Magnetic data using a towed proton precession
  magnetometer.
• Basic filtering and noise reduction carried out
  at sea.
• Additional processing may include a 3-dimensional
  inversion with the bathymetry to solve for
  seafloor magnetization.
• This removes the effects of seafloor bathymetry
  and magnetic skewness.
• Processing software is all available freely and
  runs on Unix/Linux based computers

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• Bathymetry of the Lau Basin (Fiji/Tonga) compiled
  from a number of sources.
• Magnetic anomaly for the basin. Note that the
  magnetic anomaly appears chaotic, and is
  difficult to interpret due to the high degree of
  skewness.
• The bathymetry and magnetic anomaly grids can be
  used to derive a magnetization grid that gives a
  much clearer view of the spreading history.

From Taylor et al., 1996
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• The R/V Maurice Ewing routinely collects
• 2. Gravity data using a BGM-3 gravimeter.
• Basic filtering and noise reduction carried out
  at sea.
• Additional processing may include the derivation
  of Bouguer and isostatic anomalies.

From Jones, 1999
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Free-air gravity anomaly of the Woodlark Basin,
Papua New Guinea, region. Compiled from a number
of sources.
From Goodliffe et al., 1999
Bouguer anomaly of the same region calculated
using the FFT method of Parker (1973). Subtleties
such as the difference in crustal thickness
between the eastern and western Woodlark Basin
become more apparent.
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And additionally 3. Hydrosweep-DS2 multibeam
bathymetry

• Example of DS2 bathymetry collected over Big
  Blue, a serpentinite seamount in the Mariana
  region.
• The data was processed with MB-System, a
  multibeam processing package available freely
  from LDEO (Unix/Linux).
• The data is displayed using GMT, a geophysical
  processing and display package available freely
  from the University of Hawaii (Unix/Linux/Mac/PC)
  .