HAWAIIMR1 Swath Mapping and Underway Geophysics Acquisition and Processing

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HAWAIIMR1 Swath Mapping and Underway Geophysics Acquisition and Processing

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Title: HAWAIIMR1 Swath Mapping and Underway Geophysics Acquisition and Processing

1
HAWAII-MR1 Swath Mapping and Underway Geophysics
Acquisition and Processing

Andrew M. Goodliffe
Department of Geological Sciences
University of Alabama

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

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.

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.
5

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.

6
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.
7

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

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
9

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
10
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.
11
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)
.