Uncovering hidden flow patterns in coastal waters likely leads to faster disaster response

Date:
June 17, 2020
Source:
Virginia Tech
Summary:
With more accurate modeling data, response teams can better predict
the search area grid from the air, and reduce emergency response
time when lives are on the line.



FULL STORY ==========================================================================
Each year, the U.S. Coast Guard performs thousands of search and rescue missions at sea. In situations where every minute matters, it is critical
to have the most efficient ocean modeling data and algorithms at hand.


========================================================================== Researchers at Virginia Tech are part of a multi-institutional group
using mathematical techniques with ocean models and experiments to better understand near-surface flow patterns and hidden flow structures. With
more accurate modeling data, response teams can better predict the search
area grid from the air, and reduce emergency response time when lives
are on the line.

Throughout this study, published in Nature Communications on May 26,
the research team has uncovered hidden transient attracting profiles --
or TRAPs - - in ocean-surface velocity data. These transient attracting profiles act as short-term collection zones for all floating objects,
debris as well as persons in the water. When incorporated into search
and rescue algorithms, the locations of the TRAPs give a more accurate prediction on regions to focus search efforts.

"From the moment they are alerted that someone is lost, search and
rescue teams use sophisticated software to try to pinpoint the last known location in the water, factor in how much time has passed, and make their
best prediction on how far they have drifted," said Shane Ross, professor
in the Kevin T. Crofton Department of Aerospace and Ocean Engineering. "By improving the modeling of drifting objects in unsteady currents, search
teams will have more efficient probability computations that enable them
to set a tighter search grid and make faster, safer rescues." Current
flow models used in search and rescue operations factor in ocean dynamics, weather prediction, and in-situ observations, such as self-locating
datum marker buoys deployed from air. According to the research team,
even with high-resolution ocean models and improved weather prediction,
search and rescue planning is still based on conventional practices, and rescuers rely on their hunches as much as sophisticated prediction tools.

Computational tools can predict how particles or objects are transported
and reveal areas of the flow where drifting objects are likely to
converge. In engineering terms, these patterns are called Lagrangian
coherent structures.

Unfortunately, calculating Lagrangian structures can often be
time-consuming and computationally expensive.

For use in disaster response scenarios, transient attracting profiles
are easily interpreted and can be computed and updated instantaneously
from snapshots of ocean velocity data. This eliminates very expensive and timely computation, especially when short-time predictions are critically important in search and rescue. After six hours, the likelihood of
rescuing people alive drops significantly.

These attracting profiles, where persons in the water are likely
to collect, provide continuously updated and highly specific search
paths. The inset shows a migrant boat that capsized on April 12, 2015
in the Mediterranean Sea.

In order to prove the predictive influence of transient attracting
profiles in coastal waters ? -- or identify the regions where objects
or people are most likely to accumulate over a two- to three-hour period
of time ? -- the research team conducted multiple field experiments off
the coast of Martha's Vineyard in Massachusetts.

Using both Coastal Ocean Dynamics Experiment drifters and 180-pound
OSCAR Water Rescue Training manikins, targets were released around areas
of predicted transient attracting profiles with GPS tracking devices
that reported location every five minutes. Even without accounting for wind-drag or inertial effects, the researchers observed that the TRAPs invariably attracted the floating drifters and manikins in the water
over a two- to three-hour period.

Identifying transient attracting profiles on ocean surface velocity data
can also have significant impact on the containment of environmental
disasters, such as catastrophic oil spills. TRAPs provide critical
information for environmental hazard response teams and have the potential
to limit the spread of toxic materials and reduce damaging impact on
the surrounding ecological systems.


========================================================================== Story Source: Materials provided by Virginia_Tech. Original written by
Jama Green. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Mattia Serra, Pratik Sathe, Irina Rypina, Anthony Kirincich,
Shane D.

Ross, Pierre Lermusiaux, Arthur Allen, Thomas Peacock, George
Haller.

Search and rescue at sea aided by hidden flow structures. Nature
Communications, 2020; 11 (1) DOI: 10.1038/s41467-020-16281-x ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200617121435.htm

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