The document summarizes NOAA's 2002-2003 bathymetric survey of the Puerto Rico Trench using multibeam sonar aboard the NOAA Ship Ronald H. Brown. The survey mapped over 22,700 square nautical miles of seafloor at depths of up to 8,800 meters, revealing submarine landslides posing a tsunami hazard. Data from this survey informed NOAA's 2015 Océano Profundo campaign using the NOAA Ship Okeanos Explorer to further study the trench with submersibles and robots. Modern multibeam sonars like those on the Okeanos Explorer provide not only seafloor bathymetry but also backscatter data that can be processed to create images revealing

1.  Hydrographic Surveying beyond Maritime Access
Marc Goossens
HZS Hydrography B 2015-16

2. Welcome aboard
 NOAA is the US government’s scientific agency
for studying and monitoring the conditions o
the oceans and the atmosphere.
 NOAA operates about 16 active oceanographic
and survey ships.

3. NOAA Ship Ronald H. Brown
oceanexplorer.noaa.gov/technology/vessels/ronbrown/ronbrown.html
Welcome aboard
 In September 2002 and March 2003, the
NOAA Survey Vessel Ronald H. Brown
performs a bathymetric survey of hitherto
uncharted depths.

4. geos309.community.uaf.edu/files/2014/09/caribbean-plate-boundaries.gif
Cuba
Hispaniola
Puerto Rico
 here, the North
American Plate is
sliding underneath
the Caribbean Plate
 this caused the
Puerto Rico Trench
= deepest trench in
the Atlantic Ocean
 at its deepest, the
Trench is 8 800
meters deep
 it extends over 800
kilometers in length.
2002—2003 NOAA Bathymetry of the Puerto Rico Trench

5. September 2002
February-March 2003.
• Multibeam bathymetry and
acoustic backscatter data were
acquired for 27 days.
• Approximately 22 700 sq
nautical miles.
• The pattern of tectonic
deformation was then used to
assess:
• seismic hazards
• and tsunami hazards
Puerto Rico
2002—2003 NOAA Bathymetry of the Puerto Rico Trench

6. geos309.community.uaf.edu/files/2014/09/caribbean-plate-boundaries.gifoceanexplorer.noaa.gov/okeanos/explorations/ex1502/background/plan/media/trench.html
Several geological discoveries were made

7. oceanexplorer.noaa.gov/explorations/03trench/summary/media/2.html
Image resolution: 150 meters²
Submarine slides indicate tsunami hazard
 Previously unclear:
 does northern insular slope of
Puerto Rico continued to tilt ?
 are submarine slides still active ?
 The newly acquired multibeam
data and imagery suggest that…
 the slope failure was an initial
phase in the landslide process;
 slumping along the northern slope
of Puerto Rico is an active and
ongoing process.
«Submarine slides are known sources of tsunamis.
The discoveries made during this expedition make clear the potential
tsunami hazard to the densely populated northern coast of Puerto Rico
if another massive slope failure were to occur during an earthquake. »


8. oceanexplorer.noaa.gov/explorations/03trench/summary/media/2.htmloceanexplorer.noaa.gov/okeanos/explorations/ex1502/background/plan/welcome.html
Survey used to plan 2015 Océano Profundo campaign
«These exciting discoveries
will form the basis for
additional expeditions that
will investigate specific
features of the sea floor by
means of submersibles and
remotely operated vehicles. »


9. Océano Profundo echosounding devices (1)
NOAA Ship Okeanos Explorer
 “workhorse” = Kongsberg EM302 30 kHz
multibeam sonar:
 seafloor bathymetry
 seafloor backscatter
 water column backscatter.
Backscatter = strength of the acoustic signal reflected
from some target: the seafloor, bubbles in the water
column…
 Knudsen Chirp 3260 3.5 kHz subbottom profiler:
 shallow seismic reflection profiles
 details about the geology below the seafloor.
This system can survey the seafloor at depths up to
10,000 meters.
 18 kHz Simrad EK60 split-beam sonar:
 single-point reflection seafloor bathymetry
 calibrated water-column backscatter.
Calibrated backscatter can be used in bubble detection
and to map biomass in the water-column.

10. EK60 split-beam
transducer mounted on
the hull of the Okeanos
Explorer.
oceanexplorer.noaa.gov/okeanos/explorations/ex1503/logs/jun6/media/ek60.html
One of the EM302
transducers being
installed on the ship’s
hull (2008).
Océano Profundo echosounding devices (2)

11. oceanexplorer.noaa.gov/okeanos/explorations/ex1301/media/mb_mapping_guide.pdf
Océano Profundo data processing pipeline
1. Raw multibeam bathymetry data files acquired by SIS
are imported into CARIS.
2. In CARIS, attitude and navigation data stored in each
file are checked, and erroneous soundings are flagged
using CARIS Swath Editor and Subset Editor.
3. Cleaned, gridded bathymetric data are exported to
ASCII text files (x,y,z) in WGS datum at resolution
commensurate with the survey depths.
4. The ASCII files are then used to create Fledermaus SD
objects.
5. These SD objects are then exported to geotiff and
Google Earth KMZ.
«Bottom and water column backscatter data are processed at sea using Fledermaus. Typical bottom backscatter
products include flat geotiffs and draped backscatter SD objects. Water column backscatter products include SD
point objects.»


12. Can we get more out of our data?
 Sidescan imaging:
 lateral illumination (ensonification)
 registers: total intensity = f (angle)  “image”
 Multibeam bathymetry
 more vertical illumination
 registers: ping return time = f (angle)  “bottom profile”
 clever processing is needed to distill this information from the
acoustic return!
 BUT:
 the received / recorded data contain much more information!
 analysis of coregistered bathymetry and this “backscatter” sets
out to exploit this...
 by reconstructing actual reflectivity per zone (seabottom, water
column)

13. seafloor
oceanexplorer.noaa.gov/okeanos/explorations/ex1404/logs/oct3/oct3.html
Full swath data = raw “backscatter fan”

14. Using multibeam backscatter
what?  target reflectivity how?  co-registration
 seafloor backscatter
= the amount of acoustic energy being received
by the sonar after a complex interaction with the
seafloor—which may be normalised.
 different bottom types “scatter” sound
energy differently:
 softer bottom (mud)  weaker signal
 harder bottom (rock)  stronger signal.
 simultaneous data acquisition:
 bathymetry
 backscatter “snippet”
 (data collected for each beam of each ping)
 Okeanos Explorer’s EM302 system logs both
types of data at the same time:
 the data are co-registered
 = they are geographically referenced together
 backscatter snippet data will always be
shown in the right place on the seafloor.

15. Benefits of multibeam backscatter data acquisition
 improves interpretation of bathymetry
 significantly better accuracy + confidence in interpretations of seabed features
and materials.
 better “baseline data” for automated mapping techniques
 values can be contoured to form feature polygons
 values can also be mathematically manipulated and merged with other datasets
which is a useful technique in creating maps for site favorability assessments.
 the resulting map
 is more reliable
 is potentially a much more detailed
 and can be created in less time.
 corrected backscatter data allows better integration with sediment
samples and subsequent quantitative discrimination.
www.sea-technology.com/features/2010/0910/multibeam_echosounder_backscatter.php

16. www.fugro-pelagos.com/papers/newdevinmulitbeambackscatter/tgpi_backscatter.htm
Now, do we really see more?
depth reflectivity
1

17. www.fugro-pelagos.com/papers/newdevinmulitbeambackscatter/tgpi_backscatter.htm
Now, do we really see more?
depth reflectivity
2

18. www.fugro-pelagos.com/papers/newdevinmulitbeambackscatter/tgpi_backscatter.htm
Now, do we really see more?
depth reflectivity
3

19. “New project deliverables” from MB backscatter
«During exploration missions where there is as
much geological and geophysical as habitat
interest, multibeam backscatter is becoming
recognized more and more as an invaluable
tool.
For this mission, the mapping team is adding a
new deliverable to our daily products that we
provide to the rest of the science team—a
backscatter image draped over multibeam
Digital Terrain Model (DTM).»
 Elaine Stuart Senior Survey Technician – NOAA Ship
Okeanos Explorer

20. oceanexplorer.noaa.gov/okeanos/explorations/ex1104/logs/aug12/aug12.html
“Draping” reflectivity over bathymetric profile
 These two images, although generated from the
same data file, provide very different information
about the same area of the seafloor.

21. oceanexplorer.noaa.gov/technology/tools/sonar/sonar-fan.html
Water column – gas seeps

22. www.qps.nl/display/fledermaus/hydrographic
Image draping in QPS Fledermaus

23. Object reflectivity imaging