found at sea and comparing actual movement to models’
predictions.
3.3. Direct detection of derelict fishing gear
Successfully selecting, testing, and initiating operation of sensor–
platform system(s) for short- and long-range direct detection
is the culminating step for at-sea detection of DFG. Once the characteristics
and behavior of DFG under various conditions are determined,
the sensor community can identify sensors capable of
collecting data with the appropriate resolution for field testing.
Direct detection sensors can range from the human eye to hyperspectral
sensors. Similarly, platform operations can range from
the subsurface (e.g., underwater autonomous vehicle), to surface
(e.g., ship), to space (e.g., satellite). The primary objective of this
component of the strategy is to develop sensor–platform systems
for short- and long-range direct DFG detection. In the direct detection
of DFG, cost efficiency must also be evaluated in selecting the
optimal coupled sensor–platform design to increase the probability
of widespread implementation. The design and choice of a system
will ultimately depend upon specific mission goals (e.g.,
targeting DFG for removal vs. estimating DFG abundance) and
operational resources.
Remote sensing experts emphasized that a critical aspect of
identifying appropriate sensors is the continued refinement of
anomaly-detection algorithms used to distinguish DFG at sea from
the surrounding environment. These are based on data from sensor
arrays. While data sets for a number of sensor technologies exist to
develop and test the detection capabilities of these algorithms,
including video, high-resolution photographs, light detecting and
ranging (LIDAR) and thermal imagery, other potentially useful sensors,
including hyperspectral imagery and SAR, have not been
tested with DFG targets (Veenstra and Churnside, 2012).
Ideally, field experiments would occur in situ at testing site(s)
equipped with anchored DFG at known locations to identify sensors
that perform best at detecting targeted DFG. Once the optimal
sensors have been identified, their specifications (size, weight,
electrical needs, etc.) and characteristics of the operational environment
can be used to select or design the sensor platform. Proposed
short- and long-range platforms could then be tested at
the field site to determine their utility. It is expected that controlled
field testing of short- and long-range platforms will be
needed to optimize performance before implementation during
at-sea DFG removal operations. Workshop participants identified
numerous gaps in knowledge related to direct detection of DFG
(see Appendix C). Actions to address these gaps are summarized
in Table 1 and detailed below.
3.3.1. Operational characteristics in derelict fishing gear accumulation
zones
Understanding the operational environment allows the selection
of appropriate sensors and sensor platforms for direct detection
of DFG. Conditions, depending upon location in the North
Pacific, can range from Beaufort 0 (calm with flat sea conditions;
middle of the N. Pacific subtropical high) to Beaufort 7 (high winds,
moderate or near gale) or higher. This type of information will inform
choices of both platform and sensor. Clearly, having accurate
and timely measurements will be crucial in implementation of direct
detection strategies and use of any sensor–platform systems.
To assist in selection of the appropriate sensor–platform system
for a given environmental state, estimations of typical wave height,
winds, other weather parameters, and additional variables of interest
must be made available to the sensor and platform research
and development groups.
Remote-sensing experts highlighted the need to increase our
understanding of the optimal temporal and spatial conditions for
detection of DFG and to develop operational requirements guidance
that classifies the appropriate sensors and sensor platforms
for various environmental states. While oceanographer participants
in the workshop agreed that information and data are available
in published studies, reports, anecdotal information, and data
sets to characterize the operational environment, a comprehensive
database accessible and available for use by sensor–platform
development groups was not at present readily available.
Workshop participants recommended further data collection or
synthesis of existing data on environmental conditions specific to
DFG detection in addition to engaging entities that might already
possess this type of information (e.g., NOAA National Weather Service,
volunteer vessel program for marine surface weather
observations).
3.3.2. Applicability of sensors and image processing
Successful use of sensors must be able to distinguish between
floating or subsurface DFG and the surrounding water, solar reflectance,
sea state (e.g., ‘‘white caps’’), and other non-target items
(e.g., marine mammals) at appropriate spatial scales across a broad
spectrum of environmental conditions.
As an early and relatively low-cost step, workshop participants
proposed working in nearshore areas to test sensors from a boat on
self-deployed or found nets. Ideally, in situ field studies of sensor–
platform systems would be conducted at an offshore testing site
with anchored DFG at known locations as noted above. Just as
the human eye works in concert with the brain to process data,
electronic sensors require the use of anomaly-detection algorithms
to distinguish DFG from the background environment (i.e., ocean
surface and water column). Additional tests of sensors and refinement
of algorithms are recommended, as is the field investigation
of potentially useful sensors, including hyperspectral imagery,
with DFG targets (Mace, 2012).
3.3.3. Appropriate platforms for detecting at-sea derelict fishing gear
Workshop participants proposed short- and long-range platforms
could be tested at established field sites to determine the
most effective combinations of sensor and platform. One scenario
includes the use of long-range platforms launched from land
(e.g., surveillance aircraft) and traveling thousands of kilometers
at relatively high speeds surveying large areas to confirm zones
of likely high DFG density identified by indirect detection. Subsequently,
or ideally concurrently, short-range platforms (e.g., UAS,
small boats), deployed from a vessel would locate individual pieces
of DFG for removal. The design and choice of systems will ultimately
depend upon specific mission goals (e.g., estimating overall
amount of DFG present in an area of ocean; directing ship navigation;
targeting items for removal).
In addition, there is enormous potential for improving information
on DFG through the insight and opportunistic observations of
fishers, shipping crews, and other ocean users. Establishment of
partnerships and collaboration with the fishing and shipping
industries and other seafarers (e.g., through yacht clubs) are potential
actions for improving data on the direct detection of DFG.
4. Discussion
Work must begin now if we are to realize the overall objectives
of early and efficient at-sea detection and removal of DFG. This
work must be collaborative and multi-disciplinary, utilizing the
expertise within oceanography, meteorology, modeling, marine
debris, remote sensing technology, and marine policy. The overall
strategy for the at-sea detection of DFG is itself multi-faceted, with
three main strategy components, each addressing different, but
related, elements. Each element possesses both unique and shared