This discussion is designed to last one week: Feb 3-10 (February 9 is a wellness day, so take that day off)Read these three articles:Smith, W. H. F., K. M. Marks, and T. Schmitt (2017), Airline flight paths over the unmapped ocean, Eos, 98, https://doi.org/10.1029/2017EO069127. Published on 08 March 2017.Picard, K., B. Brooke, and M. F. Coffin (2017), Geological insights from Malaysia Airlines flight MH370 search, Eos, 98, https://doi.org/10.1029/2017EO069015. Published on 06 March 2017.Full fathom five; Oceanic cartography. The Economist, 9 Jan. 2021, p. 70(US). Gale In Context: Global Issues, link.gale.com/apps/doc/A647711443/GIC?u=psucic&sid=GIC&xid=0f13ad1d. Accessed 14 Jan. 2021.I have posted some questions for discussion so keep those in mind while you read.When you reply to the discussion threads, don’t feel like you have to come up with a full and complete answer. I am actually more interested in partial answers that move the discussion along, so post one or two thoughts that interested or confused you the most. If you feel like your thought has already been said by a classmate, move things along by asking a question or clarifying or adding another detail.Please show up and participate multiple times during the week devoted to this discussion.Your grade is based on the quality of your participation, not whether you are “right” about what you say, and not by the sheer number of posts. See my discussion grading rubric for more details.Geological Insights from Malaysia Airlines Flight MH370 Search – Eos
https://eos.org/science-updates/geological-insights-from-malaysia-air…
Geological Insights from Malaysia Airlines Flight MH370
Search
A rich trove of marine geophysical data acquired in the search for missing
flight MH370 is yielding knowledge of ocean floor processes at a level of
detail rare in the deep ocean.
One by-product of the search for the missing Malaysian Airlines flight MH370 is a view with an
unprecedented level of detail of the landscape deep in the Indian Ocean. This 3-D image shows the
Diamantina Escarpment, looking northwest (upslope). The largest seamount in this area, about 1.5
kilometers high, appears in the foreground. In the middle and background, the escarpment and
trough mark the northern margin of the rift. Vertical exaggeration is 3 times. Credit: Kim Picard and
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Jonah Sullivan.
By Kim Picard, Brendan Brooke, and Millard F. Coffin ! 6 March 2017
The tragic disappearance of Malaysia Airlines flight MH370 (http://onlinelibrary.wiley.com/doi/10.1002
/2014EO210001/abstract)
on 8 March 2014 led to a deep-ocean search effort of unprecedented scale and
detail. Between June 2014 and June 2016, geophysical survey teams aboard ships used echo sounding
techniques to create state-of-the-art maps of the seafloor topography and profiles of the sediments
below the ocean floor in a zone spanning about 279,000 square kilometers of the southeastern Indian
Ocean.
(https://eos.org/?attachment_id=69033)
Fig. 1. Satellite-derived gravity field (gray) [Sandwell et
al., 2014] and multibeam echo sounder (color) data
were used to produce these maps of the MH370 search
area in the southeast Indian Ocean. The relief models
are shown in Sun-illuminated (shaded relief) mode.
The inset map shows the MH370 search area that was
mapped with multibeam echo sounding (shown in
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red). This map highlights the Southeast Indian Ridge
(SEIR) and the Kerguelen Plateau, and it includes
estimated spreading rates of the SEIR [Argus et al.,
2011], lines delineating regions of approximately equal
age (isochrons [Müller et al., 2008]), and
interpretations of SEIR segments (I–VII [Small et al.,
1999]). Other abbreviations are AAD, AustralianAntarctic Discordance; CIR, Central Indian Ridge;
RTJ, Rodriguez Triple Junction; SWIR, Southwest
Indian Ridge; WA, Western Australia. The larger map
shows details of the ocean depth mapping effort using
multibeam echo sounder bathymetry data. Locations
of Deep Sea Drilling Project (Leg 26) and Ocean
Drilling Program (Legs 121 and 183) Sites 255, 752 to
755, 1141, and 1142 are also indicated, as are the
locations of Figures 2, 3, and 4. Click image for larger
version.
The curved search swath is 75 to 160 kilometers wide, and it sweeps from northeast to southwest. It
centers on Broken Ridge and extends roughly 2500 kilometers from the eastern flank of Batavia
Seamount to the Geelvinck Fracture Zone (Figure 1). Aircraft debris found along the shores of the
western Indian Ocean is consistent with drift modeling that indicates the aircraft entered the sea in
the search area (https://www.atsb.gov.au/mh370/).
The data set that emerged from this search effort constitutes the largest high-resolution multibeam
echo sounder (http://www.ga.gov.au/about/projects/marine/mh370-bathymetric-survey/mh370-multibeam-sonar) (a
type of sonar) mapping effort for the Indian Ocean, covering an area about the size of New Zealand.
Previous ocean floor maps in this region had an average spatial resolution (pixel size) of more than 5
square kilometers, but the new maps resolve features smaller than 0.01 square kilometer (an area
slightly larger than a soccer field). Crucially, the new data provided the geospatial framework for the
last phase of the search (http://www.ga.gov.au/about/projects/marine/mh370-bathymetric-survey), in which search
teams deployed deepwater, high-resolution acoustic and optical imaging instruments with the ability
to identify aircraft wreckage.
A Sharper Focus on the Ocean Floor
The global ocean covers 71% of Earth’s surface, yet the ocean floor remains poorly studied compared
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to the land surface. In particular, knowledge of ocean floor topography is sparse because light cannot
penetrate the deep ocean and acoustic mapping techniques are relatively inefficient in mapping its
floor. Most of the ocean floor (85%–90%) has been mapped indirectly using satellite-derived gravity
data, which yield a spatial resolution of about 5 kilometers [Weatherall et al., 2015]. By comparison,
topographic maps of even the most remote land areas on Earth resolve features approximately 50
meters across, and topographic maps of the Moon, Mars (https://eos.org/research-spotlights/how-mars-got-itslayered-north-polar-cap),
and Venus resolve 100-meter features [Copley, 2014].
The high-resolution multibeam echo sounder data set that emerged from this search effort covered an
area about the size of New Zealand.
Ship-mounted multibeam echo sounders that use sound waves that echo off the ocean floor provide
much finer and more accurate topographic data (https://eos.org/project-updates/new-insights-from-seafloormapping-of-a-hawaiian-marine-monument)
for the deep ocean floor with a spatial resolution (as distinct from
a vertical resolution) of at least 100 m in 5000-meter water depths. However, only 10%–15% of the
ocean basins have been mapped using multibeam echo sounders [Weatherall et al., 2015].
This technique also records acoustic backscatter from the ocean floor, which can be used to
distinguish between hard rock and soft sediment. Such fundamental spatial information is essential
for characterizing the physical features of the ocean floor, for making inferences on geological and
oceanographic processes, and for identifying the habitats of species that live on the ocean floor.
A Complex Region
Beyond the continental margins, toward the open sea, the floor of the Indian Ocean is a complex
mosaic of normal oceanic crust (not associated with hot spots and other anomalies), submarine
plateaus and ridges, seamounts (https://eos.org/project-updates/a-name-directory-for-the-ocean-floor), sea knolls,
and microcontinents. Various processes, including seafloor spreading (including ridge jumps
(http://www.nongnu.org/magellan/magellan_ridgejump.html)),
flood and hot spot magmatism, and tectonism,
produce a variety of features.
Only 10%–15% of the ocean basins have been mapped using multibeam echo sounders.
The MH370 search area includes all of the major elements of the mosaic, and it lies in water depths
between 635 and 6300 meters (Figure 1). The search teams mapped most of the area with a 30kilohertz multibeam echo sounder system (Kongsberg EM302, M/V Fugro Equator), and they
mapped much smaller areas with 12-kilohertz systems, which can reach the deeper ocean floor
(Kongsberg EM122, M/V Fugro Supporter; Reson SeaBat 8150, Chinese PLA Navy ship Zhu Kezhen).
Here we highlight three examples from this shipboard multibeam echo sounder data set that are
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helping to illuminate the geologic development of this portion of the Indian Ocean.
Submarine Plateau Rifting and Breakup
Broken Ridge and the Kerguelen Plateau formed mostly as a contiguous large igneous province
(http://www.largeigneousprovinces.org/)
/cretaceous.php)
in Cretaceous time (http://www.ucmp.berkeley.edu/mesozoic/cretaceous
[Coffin et al., 2000]. They subsequently experienced rifting and were eventually
separated by seafloor spreading along the Southeast Indian Ridge (SEIR) 43 million years ago
[Mutter and Cande, 1983].
The southern flank of Broken Ridge, known as the Diamantina Escarpment, documents the rifting,
plunging more than 5100 meters from its crest (638 meters of water depth) into a deep trough (5800
meters of water depth). This rifted flank includes escarpments (http://www.nationalgeographic.org
/encyclopedia/escarpment/)rising
more than 1000 m above the ocean floor, slopes as steep as 67°, and
fault blocks about 12 by 25 kilometers in size and rising more than 1200 meters above their base
(Figure 2).
Fig. 2. Three-dimensional model looking east of the rifted southern flank of Broken Ridge (northern
part of the rift valley) along the Diamantina Escarpment. Slopes commonly exceed 10°, and they
increase to more than 35° along the margins of the Diamantina Trench. Large-scale ocean floor
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features include escarpments (as much as 1200 meters high), detachment blocks, grabens, and areas
of planar floor within the trench as wide as 10 kilometers. High backscatter intensity and angular
morphology indicate that bedrock is exposed in a few places at and near the top of the ridge and on
the flank down to depths of about 1350 meters. Parallel WSW–ENE lineations on some scarps,
extending to water depths of about 2400 meters, most likely represent exposed steeply dipping
bedding planes. Mass wasting, a downslope movement of loose rocks and sediment during and after
the rifting process, has incised the escarpment, and significant sediment has accumulated in the
grabens and at the bottom of the Diamantina Trench (see Figure 1 for location).
The new multibeam echo sounder data, integrated with preexisting seismic reflection and drilling
data, illuminate exposed igneous basement rock, prerift sedimentary sections, and overlying sediment
that accumulated on the ocean floor during (hemipelagic sediment) and after (pelagic sediment)
rifting.
The morphology and seismic stratigraphy of the Diamantina Escarpment indicate that the mode of
rifting resembled an orthogonal rift model, in which faults develop parallel to the axis of spreading.
Between the faults, a series of elongated blocks of crustal material, grabens, steps down into a deep
trough and abuts the spreading ridge volcanics [Karner and Driscoll, 1993].
Seafloor Erosion
North of its rifted southern flank, Broken Ridge generally has subtle relief, with igneous basement
rocks overlain by sedimentary rock and pelagic sediment [e.g., Coffin et al., 2000]. In places, slides
and debris flows have reworked sediment downslope.
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Fig. 3. The differences in resolution between multibeam
and satellite-derived bathymetry data for the northern
flank of Broken Ridge are apparent here. Numerous
mass wasting features are evident, including slides and
debris flows (delineated by their head scarps) that
crosscut and run out as debris fans into the large
semicircular depression (see Figure 1 for location).
A large depression, about 90 kilometers in diameter and with about 500 meters of relief, lies some 70
kilometers northeast of the crest of Broken Ridge (Figure 3). Numerous crosscutting retrogressive
slides (where the collapsing area extends progressively higher up the slope) and debris flows dissect
the flanks of the depression, recording episodes of sediment flow, with slide scarps as much as 180
meters high and 10 kilometers wide and debris fans more than 150 kilometers long.
Tectonic Spreading Fabric
South of Broken Ridge, normal oceanic crust of the Australian-Antarctic Basin has formed along the
SEIR at intermediate spreading rates of 59–75 millimeters per year [Small et al., 1999; Müller et al.,
2008]. The shipboard multibeam echo sounder data swath traverses a region of crust north of the
SEIR that is some 10 to 40 million years old, obliquely cutting across tectonic seafloor spreading
fabric consisting of elongated abyssal ridges and fracture zones (Figure 1).
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Oceanic crust in this region, which lies in water depths of 2200 to 5000 meters, is characterized by
SEIR and paleo-SEIR segments some 200 to 500 kilometers long (Figure 1) [Small et al., 1999]. In
the search area, fracture zone valleys are as much as 900 meters deep and 12 kilometers wide. The
abyssal ridges have as much as 200 meters of relief and are more than 70 kilometers long (Figure 4).
Fig. 4. Multibeam echo sounder bathymetry map of two regions of the ocean floor around the
Geelvinck Fracture Zone in the Australian-Antarctic Basin south of Broken Ridge (see Figure 1 for
locations). The fracture zone offsets the SEIR by about 310 kilometers (Figure 1, inset). The rightlateral transform fault motion (a person standing on one side of the fault would see the opposite side
displaced to the right) that created this fracture zone was mostly horizontal. Note the fracture zone
fault valleys, mid-ocean ridge spreading fabric, and isolated volcanoes.
Discontinuities along the paleo-SEIR not associated with transform faults and more than 150 sea
knolls and seamounts are also common (Figure 4). Volcanoes occur in isolation and in chains,
forming semiconcentric structures, some as high as 1500 meters, with diameters of about 500 meters
to more than 15 kilometers and slopes of about 10° to 30°.
Gaining Useful Knowledge from a Tragic Event
The new data highlight the topographic complexity of the ocean floor and provided a framework for
deploying deepwater instruments in the search for MH370 wreckage.
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The new multibeam echo sounder data highlight the topographic complexity of the ocean floor and
provided a framework for deploying deepwater instruments in the search for MH370 wreckage. The
data also revealed details of the tectonic, sedimentary, and volcanic processes that formed this region
of the ocean. This effort demonstrates the breadth and depth of knowledge that will be gained as the
remaining 85% to 90% of the global ocean is mapped at similar resolution.
Acknowledgments
We thank the Geoscience Australia team, especially Tanya Whiteway and Maggie Tran, for project
management; Maggie Tran, Justy Siwabessy, Michele Spinoccia, Jonah Sullivan, and Jonathan
Weales for data processing and mapping; and Silvio Mezzomo and David Arnold for the figures. We
are thankful for insightful reviews by Scott Nichol and Ron Hackney of Geoscience Austrialia and two
anonymous reviewers. The search for MH370 was managed by the Australian Transport Safety
Bureau and the Joint Agency Coordination Centre for the Malaysian government. We thank the Fugro
Survey Pty. Ltd. team from Perth, Australia, and the masters and crews of M/V Fugro Equator, M/V
Fugro Supporter, and Zhu Kezhen for shipboard multibeam echo sounder data acquisition.
References
Argus, D. F., R. G. Gordon, and C. DeMets (2011), Geologically current motion of 56 plates relative to the no net
rotation reference frame, G e o c h e m . G e o p h y s . G e o s y s t ., 1 2 , Q11001, https://doi.org/10.1029/2011GC003751
(https://doi.org/10.1029/2011GC003751).
Coffin, M. F., F. A. Frey, and P. J. Wallace (2000), P r o c e e d i n g s o f t h e O c e a n D r i l l i n g P r o g r a m , I n i t i a l
Re p o r t s , vol. 183, 101 pp., Ocean Drill. Program, College Station, Texas.
Copley, J. T. (2014), Just how little do we know about the ocean floor?, C o n v e r s a t i o n , 9 Oct. 2014,
http://theconversation.com/just-how-little-do-we-know-about-the-ocean-floor-32751 (http://theconversation.com/justhow-little-do-we-know-about-the-ocean-floor-32751).
Karner, G. D., and N. W. Driscoll (1993), Rift flank topography and extensional basin architecture: Formation of
Broken Ridge, southeast Indian Ocean, A n . A c a d . B r a s . C i e n c . , 6 5 , suppl. 2, 263–294.
Müller, R. D., M. Sdrolias, C. Gaina, and W. R. Roest (2008), Age, spreading rates, and spreading asymmetry of
the world’s ocean crust, G e o c h e m . G e o p h y s . G e o s y s t . , 9, Q04006, https://doi.org/10.1029/2007GC001743
(https://doi.org/10.1029/2007GC001743).
Mutter, J. C., and S. C. Cande (1983), The early opening between Broken Ridge and the Kerguelen Plateau,
E a r t h P l a n e t . S c i . L e t t . , 6 5 , 369–376, https://doi.org/10.1016/0012-821X(83)90174-7 (https://doi.org/10.1016
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/0012-821X(83)90174-7).
Sandwell, D. T., R. D. Müller, and W. H. F. Smith (2014), New global marine gravity model from Cryo-Sat-2 and
Jason-1 reveals buried tectonic structure, S c i e n c e , 3 4 6 , 65–67, https://doi.org/10.1126/science.1258213
(https://doi.org/10.1126/science.1258213).
Small, C., J. R. Cochran, J.-C. Sempéré, and D. Christie (1999), The structure and segmentation of the Southeast
Indian Ridge, M a r. G e o l . , 1 6 1 , 1–12, https://doi.org/10.1016/S0025-3227(99)00051-1 (https://doi.org/10.1016
/S0025-3227(99)00051-1).
Weatherall, P., K. M. Marks, and M. Jakobsson (2015), A new digital bathymetric model of the world’s oceans,
E a r t h S p a c e S c i . , 2 , 331–345, https://doi.org/10.1002/2015EA000107 (https://doi.org/10.1002/2015EA000107).
Author Information
Kim Picard (email: kim.picard@ga.gov.au) and Brendan Brooke, Geoscience Australia, Canberra, ACT; and
Millard F. Coffin, Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Australia; and
Woods Hole Oceanographic Institution, Woods Hole, Mass.
E d i t o r ’s n o t e : F o r m o r e o n h o w m u c h o f t h e s e a f l o o r u n d e r c o m m e r c i a l f l i g h t p a t h s r e m a i n s u n m a p p e d ,
r e a d t h i s o p i n i o n p i e c e ((hhttttppss::////eeooss..oorrgg//ooppiinniioonnss//aaiirrlliinnee–fflliigghhtt–ppaatthhss–oovveerr–tthhee–uunnmmaappppeedd–oocceeaann)) o n E o s . o r g .
Citation: Picard, K., B. Brooke, and M. F. Coffin (2017), Geological insights from Malaysia Airlines flight MH370 search, Eos,
98, https://doi.org/10.1029/2017EO069015. Published on 06 March 2017.
Text © 2017. The authors. CC BY 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright
owner is prohibited.
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Airline Flight Paths over the Unmapped Ocean
An assessment of ocean depth knowledge underneath commercial airline
routes shows just how much of the seafloor remains “terra incognita.”
Most airline passengers have no idea how little of the ocean floor beneath them has been mapped.
Credit: nateemee/iStock.com
By Walter H. F. Smith, Karen M. Marks, and Thierry Schmitt ! 8 March 2017
It has been 3 years since Malaysia Airlines flight MH370 disappeared (http://onlinelibrary.wiley.com
/doi/10.1002/2014EO210001/abstract),
and no trace of it on the seafloor has yet been found. MH370 is
believed to have deviated from its intended flight path. Yet even the typical routes taken by overseas
flights are often over unknown seafloor.
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Of the total over-ocean distance covered by all unique overseas flight routes, 60% is above unmapped
areas.
In fact, of the total over-ocean distance covered by all unique overseas flight routes, 60% is above
unmapped areas. The quality of mapping that does exist varies widely, and the lack of data and
variance in quality hinder searches for missing aircraft, hazard assessments, and the pursuit of
baseline scientific knowledge. A modest effort could fix this lack of data.
Uneven Coverage
Only a small percentage of Earth’s seafloor has been mapped [Copley, 2014; U.S. National Ocean
Service, 2014]. For example, Smith and Marks [2014] reported that only 5% of the southeast Indian
Ocean seafloor was covered by echo soundings on 8 March 2014 when Malaysia Airlines flight MH370
went missing.
Since their publication, the MH370 search area was moved to an area where data coverage was only
1% at the time the aircraft was lost. In January 2017, the search was suspended
(http://minister.infrastructure.gov.au/chester/releases/2017/January/dc013_2017.aspx)
after 120,000 square
kilometers had been mapped (https://eos.org/project-updates/geological-insights-from-malaysia-airlines-flightmh370-search)
in efforts to find the aircraft. This is roughly 1/3 of the area shown in Figure 1 and
0.0336% of the area of Earth’s ocean floor.
Fig. 1. From left to right, shaded relief images of the seafloor terrain in 800 × 600 kilometer regions
containing the search areas for EgyptAir flight MS804, Malaysia Airlines flight MH370, and Air
France flight AF447. Approximate search areas are outlined in red. Seafloor terrain models are from
the EMODnet Bathymetry Consortium [2016] and Weatherall et al. [2015]. Note the variance in
search area, seafloor resolution, and ship tracks over the search area.
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Fig. 2. Depth measurements available at the time of the EgyptAir flight
MS804, Malaysia Airlines flight MH370, and Air France flight AF447
crashes (black dots).
In contrast, 86% of the eastern Mediterranean seafloor is mapped in the region where EgyptAir flight
MS804 crashed on 19 May 2016, and 30% of the equatorial Atlantic is mapped where Air France flight
AF447 fell on 1 June 2009. Comparing these three search regions at the same scale shows that ocean
mapping varies enormously from region to region (Figure 2). The AF447 search region also illustrates
the strong bias toward mapping of mid-ocean ridges at the expense of other areas [Smith, 1998].
Following the Airplanes
To illustrate the extent of ocean mapping under aviation routes, we compiled a list of these routes
using data from the Open Flights (http://openflights.org/) project on GitHub. These data list the
originating and terminating airports of regularly scheduled commercial flights and whether or not the
service is nonstop.
The actual path taken by any particular flight is determined as air traffic controllers direct each flight
to a sequence of waypoints and may change as weather and traffic loads change. We did not have this
level of detail, so we approximated flight routes as great circles connecting the originating and
terminating airports. Since the Open Flights data do not indicate the locations of intermediate stops,
we analyzed only nonstop routes.
Some pairs of airports (e.g., New York’s Kennedy and London’s Heathrow) are served by many
airlines flying many flights in each direction, but our analysis used each unique pair of airports only
once, regardless of the frequency of flights between its airports.
We generated a great circle route connecting each airport pair, sampled that route every 1 kilometer of
distance along its path, and then classified each sample point as being over mapped ocean, over
unmapped ocean, or not over ocean. We found that the total distance along any individual route
includes as many as 9201 kilometers flown over unmapped ocean (Figure 3, left). Half of all overocean routes fly more than 200 kilometers over unmapped ocean, and 10% of the over-ocean routes
fly more than 2000 kilometers over unmapped ocean. The longest contiguous unmapped ocean
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segment along any one route (Figure 3, middle) is 2293 kilometers, traveled when flying between New
York’s John F. Kennedy and Beijing’s Chongqing airports, and more than 20% of routes have a
longest unmapped segment exceeding 200 kilometers. On most routes, more than half of the overocean portion is over unmapped ocean (Figure 3, right).
Fig. 3. Great circle routes of commercial airline flights, showing (left) total distance along each route
that is over unmapped ocean, (middle) the longest segment of any route that is over unmapped ocean,
and (right) the relative fraction of each route that is over unmapped ocean (ratio of total unmapped
ocean distance to total ocean distance).
We found a total of 19,024 unique nonstop routes. Of these, 11,665 fly at least 1 kilometer over ocean,
and 10,686 fly at least 1 kilometer over unmapped ocean. The total route distance is slightly more
than 33.4 million kilometers, 33% of which is over ocean, with 60% of the total over-ocean distance
being over unmapped ocean. These numbers do not indicate the probability that an aircraft or a
passenger is over unmapped ocean because our analysis is unable to account for the number of
aircraft and passengers flying each route over a given period of time.
Our Criteria
An analysis like our airline route survey has to define how many depth readings it takes to list an area
as mapped. Depth measurements that can be readily obtained and used without specialized access,
licensing, or payment, which we call “available” data, are quite variable in their sampling density and
in the age, technology, and accuracy of the sounding and navigation systems used. All these variations
are irregularly distributed over the globe [Smith, 1993; Wessel and Chandler, 2011].
We divided the global seafloor area into equal-area square tiles 1 nautical mile on a side and
considered any tile mapped if it contained one or more available echo soundings. For context, modern
hull-mounted multibeam echo sounders (MBES) map a swath of the ocean along the ship’s path, but
the vast majority of available data (95% of coverage by area) are point values—one depth
measurement at one place, typically an analog measurement made by a wireline or a single-widebeam acoustic sounder [Smith, 1993].
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Only 8% of the global ocean is mapped.
Our method produces a generous overestimate, with some tiles having only one sounding. Also, the
majority of available data are poorly navigated and error prone [Smith, 1993; Wessel and Chandler,
2011]. Even by this generous definition, however, only 8% of the global ocean is mapped [Wessel and
Chandler, 2011, Figure 8].
In the 92% of ocean area where depth has not been measured, satellite altimetry interpolates the gaps
between available soundings [Smith and Sandwell, 1997; Becker et al., 2009; Weatherall et al.,
2015]. This approximation strongly underestimates seafloor topography and roughness [Becker and
Sandwell, 2008], with a variety of consequences that affect sciences, from earthquake and tsunami
hazard assessment [Mofjeld et al., 2004] to ocean circulation [Gille et al., 2004] and mixing [Kunze
and Llewellyn Smith, 2004] and climate forecasts [Jayne et al., 2004].
Addressing the Data Shortage
All of Earth’s ocean floors deeper than 500 meters could be mapped at a total cost of $2–3 billion.
All of Earth’s ocean floors deeper than 500 meters (i.e., exclusive of territorial waters and continental
shelves) could be mapped by GPS-navigated MBES for 200 ship-years of effort (e.g., 40 ships working
for 5 years), at a total cost of US$2–3 billion [Carron et al., 2001]. According to the NASA scientists
we consulted, this is less than the cost of NASA’s next mission to Europa.
We hope that our survey of the state of ocean mapping from the perspective of over-ocean flight
routes makes the relevance of ocean mapping and the current lack of mapping information clear to
the public.
Acknowledgments
Comments by two anonymous reviewers improved the manuscript. The views expressed here are
solely those of the authors and do not constitute a statement of policy, decision, or position on behalf
of NOAA or Service Hydrographique et Oceanographique de la Marine or the U.S. or French
governments.
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Full fathom five; Oceanic cartography
Date: Jan. 9, 2021
From: The Economist
Publisher: Economist Intelligence Unit N.A. Incorporated
Document Type: Article
Length: 759 words
Content Level: (Level 4)
Lexile Measure: 1250L
Full Text:
How to map the seabed from the sky
AN ALIEN SEEKING a name for the third planet from the sun might reasonably plump for “Sea” or “Ocean”, rather than “Earth”. Twothirds of its surface is covered by salt water, and its predominant colour, viewed from far away in space, is blue. What underlies all
this brine, though, remains surprisingly mysterious to the planet’s ape-descended inhabitants. As recently as 2019, for example,
researchers found several thousand new underwater mountains, known as seamounts, by measuring the effects of their gravity on
the ocean’s surface. More such discoveries almost certainly await.
One important reason for ignorance about the seabed is the lack of a tool that can easily map its topography from an aircraft flying
above the water. That, though, is about to change. Researchers at Stanford University, led by Amin Arbabian, an electrical engineer,
have developed what they call the Photoacoustic Airborne Sonar System, PASS. This makes it possible to scan the ocean floor
rapidly, from a helicopter, rather than relying on a slow-moving ship or submarine.
The problem to be solved is that sound waves, in the form of sonar, are the only reasonable way to accomplish such mapping. Both
light beams and the radio waves of radar are rapidly absorbed by water. Sound, by contrast, propagates well. What it does not do
well is cross the boundary between water and air. When this happens its amplitude is diminished a millionfold. That diminution
applies in both directions, so a pulse of sonar broadcast from an aircraft and reflected back to it from the sea floor would have a
trillionth of its original amplitude. Expecting to detect such a reflection would be a fool’s errand.
PASS partly overcomes the air-sea boundary problem by circumventing the first of those crossings. It does so by generating the
sonar pulses not on board the aircraft but rather in the water itself, using intense bursts of laser light fired at the water’s surface.
These heat the water, causing rapid expansion. That generates a sound wave which propagates to the sea floor, whence it is
reflected back to the surface. Only then does it cross the energy-sapping interface between water and air. Though that still weakens
the signal a lot, the other part of PASS, a device called a CMUT, is sensitive enough to detect it.
CMUT stands for capacitive micromachined ultrasonic transducer. As its name suggests, it is a species of electrical capacitor, and,
like all such, it is composed of two parallel plates. Any disturbance of these plates, such as the vibration induced by a sound wave,
changes the capacitor’s properties in a way that is easily detected.
CMUTs were developed at Stanford two decades ago. They are widely used in ultrasonic medical scanners and are made in the
same way as the micro-electromechanical deceleration sensors which trigger the deployment of car air bags, so they can be mass
produced. PASS employs CMUTs tuned to resonate at the exact frequency of the sonic pulse generated by the laser. This has the
double benefit of improving reception and filtering out background noise.
Preliminary tests in a university fish tank used a laser weighing 50kg, but this was a general-purpose device and the apparatus could,
the team reckon, be scaled down to weigh just a few kilograms. That would fit on commercial camera-carrying drones. A device this
size would be able to “see” through tens of metres of water, making it suitable for use above rivers, lakes and coastal waters. A larger
version for deep-sea operations would fit on a manned helicopter or a larger drone and would be able to peer down to depths of
hundreds, and eventually thousands, of metres. The team’s researchers imagine fleets of such drones making short work of the task
of charting the abyss.
Deep thoughts
Besides the scientific value of mapping the seabed with the sort of resolution normal for terrestrial cartography, PASS will also be
able to locate the wrecks of missing ships and aircraft, and engage in commercial tasks such as monitoring underwater infrastructure
like oil and gas pipelines.
There are military applications, too, particularly for the detection of submarines. In this context it is no surprise that the project is being
sponsored by America’s Office of Naval Research. But for inhabitants of the third rock from the sun–or, at least, for those of them
interested in hidden aspects of the orb they inhabit–the generation of the first high-resolution map of all of that orb’s solid surface will
be a matter of moment in its own right.
Copyright: COPYRIGHT 2021 Economist Intelligence Unit N.A. Incorporated
http://store.eiu.com/
Source Citation (MLA 8th Edition)
“Full fathom five; Oceanic cartography.” The Economist, 9 Jan. 2021, p. 70(US). Gale In Context: Global Issues,
link.gale.com/apps/doc/A647711443/GIC?u=psucic&sid=GIC&xid=0f13ad1d. Accessed 14 Jan. 2021.
Gale Document Number: GALE|A647711443
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