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Methods for Detection of Floating Debris

Report No: RPT-46-GS-11

Report Version: 1.0

Report Version Date: 12/06/2011

GLA/DfT Confidential

Summary Report based on the study by Oxford Creativity

RPT-46-GS-11 GLA confidential

Version Date: 12 June 2011 of 22 Version: 1.0

Lead Author Reviewer Approved for Release

George Shaw Martin Bransby Nick Ward

Principal Dev Engineer R&RNAV Manager Research Director

GS MB NW

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Executive Summary

Under the new Wreck Convention, the GLAs may in future take on a statutory duty to detect and deal with floating debris that poses a hazard to shipping. Such debris includes containers, timber, wooden pallets and other cargo lost from ships. This preliminary study considers methods by which this duty can be performed in a cost effective manner, demonstrating due diligence. The results of the study provide evidence of GLA preparedness to take on such a role.

Detecting and locating floating debris presents an additional task somewhat different from the existing marking of wrecks. This study, undertaken by Oxford Creativity on behalf of R&RNAV, has identified and evaluated methods of reliably, efficiently and affordably detecting a variety of floating debris throughout UK waters. Floating debris is by its nature very diverse, in terms of its size, spatial distribution and constituent materials. Much of the debris will float low in the water, possibly submerging intermittently, which presents a significant challenge for systems deployed for detection.

As an initial study, the objective is to identify candidate technologies, sensors, systems and methods of reliable detection of floating debris. It presents a broad categorisation of the surveillance task and analyses potential solutions as combinations of sensors and platforms from which they can be deployed. At this stage, until the details of the new Wreck Convention are defined, it principally signposts the direction for further investigation of solutions. The approach of the study has been to review available sensor technologies and their applicability for debris detection from fixed observation stations and mobile platforms: among others, these include satellite imagery, airborne radar and lidar, shipboard optical, FLIR and sonar sensing.

Since 1996, there have been approximately 10,000 accidents reported to the Marine Accident Investigation Board (MAIB). Of these, some 200 have been caused by floating or submerged debris. Although cargo containers are the highest profile of types of floating debris, the frequency of occurrence of confirmed collisions with cargo containers is very low and wooden debris is much more likely to be the cause of damage and incident.

The task of detecting floating debris is a massive challenge given the extent of the sea surface area to be surveyed and the relatively small size of the component debris to be detected – less than 1m2 in roughly 60,000 km2 for UK territorial waters (12 n.m. limit), increasing to 750,000 km2 for the 200 n.m. limit of the UK Exclusive Economic Zone (EEZ). In the worst case, detection of debris could result in high costs for many of the technologies investigated. For mobile sensors, the costs are driven primarily by the high cost of the deployment of the sensor platform – such as aircraft or satellite – that is able to cover the sea surface area with sufficient frequency to have an impact. In the case of aircraft, the cost may be in the order of £5 for each square kilometre of sea served or half a million pounds for each scan of UK territorial waters.

It is concluded that families of detection systems, optimised for the category of surveillance, may be necessary to detect floating debris of many different types. Three principal surveillance categories have been identified, each with their associated potential detection solutions:

wide area surveillance using high resolution satellite imagery and side-looking airborne radar (SLAR);

narrow area surveillance using fixed shore-based radar stations in areas such as port approaches;

local pinpoint search from a ship at sea using optical, Forward Looking Infra Red (FLIR), radar and sonar sensors, possibly deployed from the wreck-marking vessel.



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Document Information

Client GLAs

Project Title Detection of Floating Debris

Deliverable Number D224 (2010/11)

Report Title Methods for Detection of Floating Debris (Summary Report)

Report Identifier RPT-46-GS-11

Report Version 1.0

Report Version Date 12 June 2011

Lead Authors George Shaw

Lead Author’s Contact Information

G Shaw GLA Research and Radionavigation Trinity House, The Quay, Harwich, Essex, CO12 3JW, UK, T: +44 1908 216291 M: +44 7766 510578 E: [email protected] W: www.gla-rrnav.org

Contributing Author(s)

iManage Location

R&RNAV Deliverable Deliverable D224 of the R&RNAV 2010/11 work programme

Work Package reference

5.2.1.3 (Detection of Floating Debris)

Deliverable Title Detection of Floating Debris – Summary Report

Circulation

1. Project Files (hard copy)

2. GLA Chief Executives

3. R&RNAV RNAV distribution list



Contents

1 Introduction ...................................................................................................................... 7

1.1 Background ............................................................................................................. 7

1.2 Scope of Study ........................................................................................................ 7

1.3 Definition of ‘Wreck’ ................................................................................................. 7

2 Scoping the Detection Problem ........................................................................................ 8

2.1 Search Area ............................................................................................................ 8

2.2 Types of Floating Debris ......................................................................................... 8

2.3 Likelihood of Incident with Floating Containers ....................................................... 8

2.4 Cost Consideration for Surveillance ........................................................................ 9

3 Survey of Sensors / Detector Systems .......................................................................... 10

3.1 Overall performance parameters of detectors ....................................................... 10

3.2 Passive Detector Systems .................................................................................... 10

3.3 Active Detector Systems ....................................................................................... 11

3.4 Indirect Detector Systems ..................................................................................... 12

4 Sensor Platforms ............................................................................................................ 13

4.1 Detection by Scanning Sensors on Fixed Platforms ............................................. 13

4.2 Detection by Scanning Sensors on Mobile Platforms ........................................... 14

4.3 Detection by Satellite Sensors .............................................................................. 14

5 Conclusions .................................................................................................................... 15

6 Recommendations ......................................................................................................... 17

A Appendix: Distribution of UK Floating Debris Incidents .................................................. 18

B Appendix: Indirect Detector Systems ............................................................................. 21

C Appendix: Glossary ........................................................................................................ 22

List of Tables

Table 1: Summary of Passive Sensors ................................................................................. 11

Table 2: Summary of Active Sensors .................................................................................... 12

Table 3: Number and Coverage of Fixed Coastal Scanning Sensors .................................. 13

Table 4: Families of Detection Systems by Category of Surveillance ................................... 16

Table 5: Summary of Indirect Sensors .................................................................................. 21



List of Figures

Figure 1: Frequency Distribution of Debris-Related Incidents .............................................. 18

Figure 2: Geographic Distribution of Reported Floating Debris Incidents ............................. 19

Figure 3: Reported Incidents in the English Channel Region .............................................. 20

Reference Documents

RD1 A Study into Methods of Detecting Floating Debris, Oxford Creativity Report, Final Version, August 2010, iManage document 23665

RD2 TRIZ innovative problem solving method, based on patent analysis, detailed at http://www.triz.co.uk/?gclid=CNyz383UqKkCFQEKfAodwSXUNA

RD3 http://oceans.greenpeace.org/raw/content/en/documents-reports/plastic_ocean_report.pdf.

RD4 “Marine Litter A Global Challenge” www.unep.org/pdf/UNEP_Marine_Litter-A_Global_challenge.pdf

RD5 BAE Systems (Insyte) HF shore-based Surface Wave Radar for wide area maritime surveillance http://www.baesystems.com/BAEProd/groups/public/documents/bae_publication/bae_insyte_data_hfswr.pdf

RD6 GeoEye satellite imagery service: http://www.geoeye.com/CorpSite/

RD7 A software system using radar environment survey marketed by Norwegian company Vissim: http://www.vissim.no/

RD8 US company Sicom radar system http://www.sicomsystems.com/.



1 Introduction

1.1 Background

Under the new Wreck Convention, the GLA may take responsibility for the detection, marking and removal of floating debris, including containers and other cargo lost from ships. The GLAs may assume a statutory duty to reduce the risk to shipping that is posed by a wide variety of floating debris, so this preliminary study seeks ways in which this duty can be performed in a cost effective manner, demonstrating due diligence.

The study has been undertaken in response to the proposal of the Nairobi ‘International Convention On The Removal Of Wrecks 2007’ that was adopted at the International Maritime Organisation (IMO) International Conference on the Removal of Wrecks held in Nairobi in 2007. The Convention provides a set of uniform international rules aimed at ensuring the prompt and effective removal of wrecks. The new convention will not come into force until ratified by at least ten IMO member states (which at the time of writing has not yet occurred).

1.2 Scope of Study

This report summarises the results of a study [RD1] (undertaken by Oxford Creativity using the TRIZ [RD2] innovative problem solving methodology on behalf of R&RNAV) to evaluate methods of detecting floating debris. The distribution, frequency and type of incidents are investigated, and the methodology for considering detector systems is described. The detector system survey outlines a number of candidate sensors and fixed or mobile platforms for their deployment, associated with different categories of surveillance. Families of detection systems are evaluated for area surveillance and survey in the vicinity of a ship.

While questioning the cost effectiveness of any possible debris detection system, this report identifies an approach comprising three levels of survey: wide area surveillance at sea, narrow area (coastal) surveillance and pinpoint searches from the GLAs’ own vessels.

1.3 Definition of ‘Wreck’

The significance of the new Wreck Convention lies in the agreed definitions of ‘Maritime Casualty’ and ‘Wreck’, as contained in Article 1 of the wreck convention:

“Maritime casualty” means a collision of ships, stranding or other incident of navigation, or other occurrence on board a ship or external to it, resulting in material damage or imminent threat of material damage to a ship or its cargo.

“Wreck”, following upon a maritime casualty, means:

(a) a sunken or stranded ship; or

(b) any part of a sunken or stranded ship, including any object that is or has been on board such a ship; or

(c) any object that is lost at sea from a ship and that is stranded, sunken or adrift at sea; or

(d) a ship that is about, or may reasonably be expected, to sink or to strand, where effective measures to assist the ship or any property in danger are not already being taken.

Thus the definition of a wreck, and the scope of the consequent obligations placed upon organisations responsible for wrecks or their consequences, is extended to include any part of a ship, or any other object lost at sea from a ship. The GLAs are well acquainted with methods of detecting conventional wrecks, but detecting and locating floating debris presents an additional and somewhat different task: hence the need for this study.



2 Scoping the Detection Problem

2.1 Search Area

The study has considered the floating debris problem within the waters of the UK Exclusive Economic Zone (EEZ); however, most of the results will be relevant in a worldwide context.

Key areas for survey are the English Channel and the entrance and exit to the Irish Sea, but areas of the UK territorial waters and contiguous zone will be important where sea room is limited by offshore installations. The prime search area is roughly 50,000 km2 for the Channel and Irish Sea and 120,000km2 for the combined territorial and contiguous zone 24 n.m. limit). The total search area of the UK EEZ would be 750,000km2. These figures govern the cost of surveillance of the various sea areas.

2.2 Types of Floating Debris

For the purpose of evaluating candidate detection systems, two very different classes of floating debris have been considered:

20ft metallic shipping containers lost overboard, floating 77% submerged below the sea surface, intermittently covered by waves. (See Appendix A of [RD1] for specifications of common types of containers. Appendix B of [RD1] discusses the flotation of lost containers at sea, in particular, their depth of submergence.)

Timber (e.g. sawn wood or lumber) or wooden pallets, with a typical piece of debris being only 1m2 of wood floating 2cm above and 20cm below the water. Timber, being non-metallic, is less responsive to some active detection techniques (such as radar).

There is anecdotal evidence that containers containing buoyant cargoes can remain afloat for considerable periods of time. A perfectly sealed 20ft container, loaded to the maximum permitted weight, would float with 77% of the container below the sea surface. Depending on sea state, a container may thus be submerged below the sea surface for significant proportions of time, intermittently breaking the surface. With only a small freeboard (that part of the container’s bulk visible above the sea surface), visual or electronic detection is likely to be difficult. This is a major factor contributing to the hazard of floating containers, especially at night or in low visibility, or during poor weather or high sea state.

2.3 Likelihood of Incident with Floating Containers

It is instructive to consider the likelihood of containers being found in global waters, and the risk of a ship’s incident (colliding or experiencing a near-miss) with a container. Assuming the total number of containers globally lost at sea per annum is 10,000 and a floating period of one week (before the container either sinks or is removed), the expected number of containers afloat globally at any time is 200.

As the total navigable area of the world is 1.8*108 km2, the expected occurrence of floating containers is approximately one container per one million km2 of sea surface. During a voyage, a cargo ship covers a nominal swathe of sea area roughly 50m x 500km (width x distance travelled) or 25km2 per day. Making a simple assumption that the spatial distribution of ships and lost containers is statistically uniform, the likelihood of an incident with a container is 1 in 40,000 (or 2.5*10-5) for each individual vessel per day. Maritime safety considerations are generally based on an ‘acceptable probability’ of incidents of the order of 10-5 per 3 hours (or 8*10-5 per day) per vessel. Hence, based on simple assumptions, the expected global rate of incidents with containers is ‘acceptable’.

However, further assuming that the size of the global SOLAS fleet is 20,000 vessels, the likelihood that a vessel somewhere in the world will experience a container incident during



any one day is roughly 40%, and globally a container incident can be expected every two days.

Clearly the risk of an incident with a container is increased in denser shipping areas such as UK and ROI waters. An indication of this higher risk can be estimated for 75,000 km2 of the English Channel and its approaches. Based on an estimate of about 400 ships in the area at any time (consistent with one ship passing through the Dover Straits every 4 minutes on average), the ratio of shipping density in the Channel to the global average density can be estimated at approximately 50. If a reasonable assumption is made that the density of lost containers in this area is only 12 times their global density (i.e. container density increases by only 25% of the increase in shipping density in the Channel, accounting for the prevailing sea conditions being relatively benign), then just one floating container (on average) will pose a hazard to shipping in the Channel at any time. The likelihood of a container incident in the Channel in any 24 hour period for each individual ship is therefore approximately 1 in 3000 (0.033%, or a probability of 3.3*10-4). Over all 400 ships in the area, the likelihood that a vessel somewhere in the Channel will experience a container incident in any one day is 12% and the expected time interval between container incidents in the Channel is approximately 8 days.

The Channel has some 10 to 100 (or more) pieces of debris per square kilometre (visible from a ship) as reported in [RD3]. This gives a broad estimate of more than 1,000,000 pieces of debris that might be visible with the naked eye from ships in the Channel. Appendix B contains an analysis of UK incidents related to floating debris, based on data from the Marine Accident Investigation Branch (MAIB).

The United Nations Environmental Programme report [RD4] lists the types of marine litter encountered in studies around the world. The two most common types of large hard litter are wooden pallets and oil drums, both of which could cause damage to light vessels. Other common types of large litter are tarpaulins and floating ropes which can cause propeller damage and be particularly dangerous close to shore or high traffic areas.

2.4 Cost Consideration for Surveillance

If a typical flotation period for a container is only one week, then an effective detection service may need to provide a frequency of surveillance with a significantly shorter period, perhaps daily. A detailed risk assessment would be necessary to determine the requirement for the surveillance frequency of any sea area, commensurate with the risk posed to mariners.

However, as an indication of the possible costs of surveillance, consider the survey of the 20,000 km2 of the English Channel on a daily basis. Assuming that surveillance is practicable 24 hours per day, the average rate of area surveyed would need to exceed 800 km2 per hour. This rate is likely to be achieved only by a mobile survey platform, such as an aircraft or satellite. These surveillance options are discussed further in section 4, for which the cost of such surveys is estimated at more than £3 per 1 km2 surveyed, equating to £2,400 per hour continuously 24 hours per day, 7 days per week. Such costs would exceed £20M per annum. Although a detailed business case would be needed to justify the eventual service costs against the benefits of avoiding incidents with floating debris, it is considered very unlikely that such a high cost could be justified. The example of daily Channel surveillance serves to show that a judicious selection of survey area, method and frequency will be necessary, carefully determined against the risk of incidents in hazardous areas.



3 Survey of Sensors / Detector Systems

3.1 Overall performance parameters of detectors

All detection sensors surveyed can be described in terms of their basic performance parameters (which are not independent):

Field of view or coverage area (instantaneous and swept over a specified time);

Probability of detection and the practical maximum detection range of different types of debris;

Resolution or pixel size, governing the ability to distinguish multiple objects of debris in close proximity to each other;

Discrimination of debris signal from background clutter signal (returned from the sea surface);

Dynamic range (affecting detection of various sizes of debris at different ranges).

The coverage and detection performance of the sensor is dependent on the platform on which it is carried. Platforms and sensor / platform combinations are discussed in section 4.

3.2 Passive Detector Systems

Passive detector systems, summarised in Table 1, have a receiver to capture signals that emanate directly from the debris or signals (from natural sources, such as sunlight) that are reflected or modified by the debris.

Signal Notes Recommendation Utility

Visible Light Optical detection systems include:

Unaided human vision Aided human vision (e.g. binoculars,

polarisers) Image Intensifier Night vision devices (which can

extend into near visible frequencies) TV cameras Satellite photography

Opportunities in good light conditions. Very large contrast possible. Swept field of view (swathe) is dependent on platform and sensor height. Investigate further.

Wide area, narrow area and local survey

IR (Passive) Forward-Looking Infra-Red camera (FLIR)

3.5 or 8-14micron wavelength

Some merit as a complement to other detection systems.

Local survey

Microwave (Passive) / Microwave Radiometer

Sea water has relatively low emissivity. Rain is a stronger emitter and reduces the contrast of the debris signal. Paint, wood and rust are all good emitters.

Possibly merits further investigation

Local survey

Magnetic Magnetometer - highly sensitive Caesium Vapour magnetometers are available, airborne and underwater.

Magnetic Anomaly Detection of metallic containers may have very limited range of the order of 100m

A limitation on shipboard use may be the effect of the metal structure of the deploying vessel.

Limited to local survey




Acoustic (Passive)

Signal considered insignificant, unless the debris is fitted with a noisemaker.

Do not pursue. None

Ultra-Violet (Passive)

Insufficient signal to distinguish Do not pursue. None

Radio (Passive)

Spontaneous emission too low at longer wave lengths.

Do not pursue. None

Table 1: Summary of Passive Sensors

3.3 Active Detector Systems

Active detector systems, summarised in Table 2, employ a system that transmits energy which reflects off the debris and is captured by the sensor’s receiver.


Acoustic (Active)

Active Sonar Systems include sidescan sonars, towed array, synthetic aperture sonars and vertical scanning sonars

The latter may be able to detect objects that protrude below the surface aeration layer, such as containers.

May consider vertical scanning sonar as a complement to above-surface systems (such as radar, visible, IR) for short range detection.

Local survey from ship

Microwave Radar

X-band (8-12 GHz) radar can provide good detection range and position location for floating metallic targets, with an all weather capability. Sideward Looking Airborne Radar (SLAR), with a real aperture and large antenna, provides extensive coverage (swathe width) and high resolution. Synthetic Aperture Radar (SAR) provides similar benefit with a reduced size of antenna.

Pursue further for detection of metallic containers.

Limited by nature of debris

Visible Light (Active)

LIDAR systems (based on a scanning laser) provide the possibility of long range operation. The short wavelength allows high resolution even from a small platform. However cloud, fog and rain severely reduce applicability.1

Consider LIDAR systems if and when system costs allow.

Wide area and narrow area survey

1 Sea water has useful spectral characteristics for selected frequencies: red light (wavelengths of around 700nm) is absorbed by sea water; blue-green light (wavelengths of around 470-530nm) will penetrate and then be refracted giving a diffuse return beam.




IR (Active) Forward-Looking Infra-Red camera (FLIR) can be combined with an IR searchlight. Robust LED-based thermal searchlights are available.

Consider IR searchlights for use in combination with FLIR camera.

Local survey

Long-wave Radar, including over-the-horizon (OTH) radar

Shore-based long-wave radar (i.e. frequencies below 1 GHz) may detect debris but provide only rough location. OTH radar (operating at HF, 3 - 30 MHz) using ionospheric reflection (backscatter of the sky wave) can detect targets the size of small craft at ranges of several hundreds of kilometres. OTH radar is limited by the large physical size of the antenna array, a mid-range blind zone, the need for target Doppler for detection against sea clutter, weather clutter and the availability of HF frequency slots.

Continue technology watch for future potential of shore-based over-the-horizon Surface Wave (OTH-SW) radar. BAE Systems offers an OTH-SW radar designed for wide area surveillance of maritime targets [RD5]. Shipboard OTH-SW radar is also feasible, although the length of antenna array may limit its practicability.

Wide area survey

Ultra-Violet (Active)

Fluorescence inducing UV

Impractical for reasons of UV danger at high intensity.

Do not pursue. None

Magnetic (Active)

Effectively ultra low frequency Radio.

Do not pursue None

Table 2: Summary of Active Sensors

3.4 Indirect Detector Systems

Indirect detection systems are summarised in Appendix B. They rely on the properties of the environment around the debris responding to a sensor such that the presence of the debris can be detected indirectly from its environment. Such a system, for example, may detect the presence of floating debris from the detected patterns of waves surrounding the debris. Many of these techniques are immature for the problem of detection of floating debris so may not merit being considered at this stage. An established technique for long-range detection of waves is over-the-horizon (OTH) HF radar, as discussed in section 3.3.



4 Sensor Platforms

4.1 Detection by Scanning Sensors on Fixed Platforms

Detection sensors could be deployed from a variety of fixed platforms. Primarily, these would be surface platforms (such as tethered buoys) or those that are raised above the surface (such as installed on a lighthouse or cliffs). Airborne ‘fixed’ platforms may also be relevant, such as moored balloons, as well as platforms fixed to the sea bed or underwater structures. Using fixed detection stations (such as land based radar), the scanned coverage area of the sea surface is limited by the horizon (proportional to the square root of the height of the sensor) and the extent to which the observation point is surrounded by water. Most sensor systems require a minimum grazing angle (i.e. the angle between the sensor beam and the sea surface) for satisfactory detection of objects that float low in the water. A minimum grazing angle of 5 degrees is a practical limit for radar detection. For sensors mounted at heights of 10m, 40m and 100m (cliffs or hills), with a 45º field of view and for grazing angles of 30º, 5º and 2º, Table 3 indicates the maximum coverage range and the approximate number of sensor stations required to cover 3000km of coastline.

Grazing Angle 30º 5º 2º

Sensor Height

Maximum Range

Number of

Sensors

Maximum Range

Number of

Sensors

Maximum Range

Number of

Sensors

10m 17m 86,000 0.1km 13,000 0.3km 5,000

40m 70m 21,000 0.4km 3,200 1.1km 1,400

100m 170m 8,660 1.1km 1300 2.9km 500

Table 3: Number and Coverage of Fixed Coastal Scanning Sensors

The indicated values in Table 3 serve to demonstrate the challenge of achieving sufficient offshore coverage using fixed coastal sensors. An extensive coastal infrastructure may be required and, even with substantial sensor mounting heights, offshore range coverage may be limited at best to a few kilometres of inshore waters.

The situation is improved for debris that floats higher in the water, as the presence of a freeboard is significant for the detection capability of the sensor. For example, a coherent X-band New Technology (NT) radar system may detect boats (including small non metallic rowing boats) at a range of approximately 40km with a mounting height of 150m (corresponding to a viewing angle of 0.2 degrees). However, for the debris categorised in section 2.2, there may be very little freeboard.

The coverage properties of coastal sensors indicate that such fixed shore stations will not provide an economic solution for the detection of floating debris over large sea areas. They may only be feasible as part of the solution, applied to limited areas of high density shipping such as port approaches.



4.2 Detection by Scanning Sensors on Mobile Platforms

The detection coverage from a moving platform (e.g. fixed or rotary wing aircraft, UAV, ship or underwater ROV) is significantly greater than for the equivalent fixed sensor, as the area scanned per unit time is the product of the platform speed and the sensor’s swathe width. An aircraft’s typical altitude for surveillance operations is 3000ft, especially for sensors limited by cloud. Cloud cover is present in the UK over 50% of the time and the median height of the cloud base is 1000m. The Coast Guard and Environment Agency services utilise an aircraft operational altitude of 3000ft routinely.

An indicative all-inclusive cost quotation for an airborne surveillance service is £1,250 to £1,500 per flight hour, aircraft operational costs dominating over the cost of the sensors. For a typical flight speed of 200km/hr and a sensor’s swathe width of 1km to 2km, each square kilometre of sea surface surveyed can be expected to cost £4 to £8.

SLAR or SAR surveillance can operate with significantly wider swathes, up to 30km, giving a lower potential cost of approximately £0.3 per 1km2 of surveyed area. However, radar would only support the detection of floating metal containers and not of the more common wooden debris.

The indicated costs of commercially operated airborne survey, even using wide SAR swathes, are significantly higher than may be justified by a business case for the detection service, as discussed in section 2.4.for sufficiently frequent surveillance over wide areas such as the Channel. This suggests that airborne surveillance would have limited utility within the overall detection solution, perhaps for specific campaigns in narrow areas where the risk of debris justifies the expense.

In implementing and maintaining a floating debris detection service, opportunities may exist to share the costs and the responsibility for providing the required resources. There are similarities between the systems, resources and procedures required for the floating debris detection task and those required by other surveillance activities. This suggests the potential for collaboration and cooperation with other surveillance service sponsors and providers, leading to potential cost savings and effectiveness gains. However, even if costs were shared, it may still not be possible to achieve the necessary frequency and density of floating debris surveillance required for all coverage areas commensurate with the level of risk to mariners.

4.3 Detection by Satellite Sensors

The Geo Eye satellite imagery service [RD6] utilises Low Earth Orbit (LEO) satellites, IKONOS and GeoEye-1, to produce high resolution imagery and services (such as buoy and vessel tracking). IKONOS, launched in 1999, provides monochrome and multispectral images with resolutions of 0.8m and 4m respectively (with a combined image resolution of 1m). It has a swathe width of 11.3 km and a revisit period of 3 days. The GeoEye-1 satellite, launched in 2008, provides better image resolution (0.4m monochromatic and 1.65m multispectral) with a 15.2km swathe width and a revisit period of less than 3 days, which may be suitable to support the detection of floating debris against a sea background.

Commercial arrangements for satellite imagery services relate costs to the number and resolution of images provided. Licences for the previous GeoEye ORBVIEW-2 / SeaWiFS imagery (lower resolution terminated at the end of 2010) cost around £75,000 per annum. Current services are likely to prove more expensive, with estimated costs of £3 to £7 per 1km2 surveyed at appropriate resolution, subject to the negotiation of a suitable commercial model.



5 Conclusions

There is no simple conclusion of a single sensor / platform combination that meets the needs for all aspects of debris surveillance. The solution will need to consider a family of detection systems (FODS), as a cooperative set of sensors and platforms. Coordinated components of the FODS may address the different categories of surveillance, the variability in size and constituent materials of floating debris, and the extent to which the debris is submerged or presents detectable freeboard.

It is helpful to consider an approach to the detection solution in terms of sensor and platform combinations that can be deployed sequentially or concurrently. It is also instructive to consider the different needs for surveillance in different sea areas, commensurate with the risk to the mariner. Hence, the solution may consider three specific categories of surveillance:

Wide Area Surveillance (WAS)

WAS would provide regular surveillance of designated wide areas, primarily to detect larger, higher risk floating debris such as containers.

Costs of WAS may be too high to be acceptable unless the frequency of survey is maintained at a low rate and the resolution of survey data is low (implying only larger items of debris can be detected). Satellite imagery and airborne survey using Synthetic Aperture Radar (SAR) are the most promising elements of a FODS for this surveillance category.

Narrow Area Surveillance (NAS)

NAS would cover surveillance for two aspects:

o Following up detections reported by WAS (or otherwise) to confirm the presence of debris and classify it according to threat.

o Surveillance of narrower ‘high’ risk areas, determined by vessel traffic analysis according to the density of shipping and the likelihood of debris occurring. This is likely to concentrate on port and harbour approach and the busy shipping areas of the Channel and its approaches

Many narrow areas of search that pose the highest risk are confined locations close to shore, such as the approach and entrance to ports. The most practical detection solution for this important sub-category of surveillance is likely to be a limited shore-based infrastructure of radars mounted on tall structures. Cooperation with ports and harbour authorities may enable costs to be shared.

NAS may also be necessary significantly offshore, beyond coverage of coastal radar. In this case, limited and focused airborne survey may be cost-effective and a range of mature sensor technologies notably LIDAR and SAR, are available. Such systems may already be deployed in associated services for which the sharing of surveillance costs with other agencies may be possible.

Local Pinpoint Search (LPS)

LPS would search for debris in the vicinity of a vessel, most likely using sensors onboard the GLA wreck marking vessel, to locate the debris so that it could be marked and ultimately removed.

There are several promising candidate sensor technologies that could be deployed from the vessel. Their effectiveness varies according to the type of debris and how low it floats in the water. A combination of sensors such as optical, radar and vertical scanning sonar (for debris that is largely submerged and presents little freeboard) is likely to be necessary.



Table 4 summarises the most promising family of detection systems that could address the three categories of surveillance.

Family of Detection Systems for each Category of Surveillance

Wide Area Surveillance (WAS)

Narrow Area Surveillance (NAS)

Local Pinpoint Search (LPS)

Optical (multispectral) satellite imagery

Airborne SAR detection of containers

Methods are relatively high cost which may be mitigated by cooperation with other agencies

Shore-based radar, mounted on tall structures

Airborne survey using o SAR o LIDAR

Methods are relatively high cost which may be mitigated by cooperation with other agencies

Short range, ship-mounted detection systems using: o optical (multispectral) o vertical scanning sonar o FLIR o radar (X-band)

Table 4: Families of Detection Systems by Category of Surveillance



6 Recommendations

The study recommendations are that the GLAs, through R&RNAV, should:

a. record the nature, location and frequency of occurrence of debris that occurs in UK waters, as more information becomes available (from sources such as the MAIB and direct observations), and determine the danger to shipping by risk analysis. Current sources of information are limited however, so this recommendation is not easily achieved. High resolution satellite imagery would be ideal for this task, if in future, it could be made available cost-effectively.

b. Obtain detailed historical weather data to analyse the possible correlation of debris occurrence with weather patterns, hence quantifying the risk according to weather conditions. Analysis of weather patterns that pose a risk could also indicate that some sensor types (e.g. optical sensing through cloud) may be least effective at times of highest risk from incidence of debris.

c. Determine the cost of incidents caused by debris. This will inform the future business case for options for detection solutions. Estimate the benefit of debris detection as an economic saving for maritime stakeholders.

d. Undertake technology watch on principal detection technologies: high resolution satellite imagery; airborne SAR; airborne LIDAR; land-based radar; shipboard optical, IR and sonar sensors.

e. Investigate the potential for shared surveillance services with other agencies such as MCA, and UKHO.

f. Monitor cost trends of commercial surveillance services.



A Appendix: Distribution of UK Floating Debris Incidents

The Marine Accident Investigation Branch (MAIB) of the Department for Transport responded to a request for data relating to reported incidents related to floating debris over he period from 1991 to March 2009. The data contains details of incidents resulting in damage (including minor damage) where MAIB identified either contact with debris or fouled propellers. The data covered reported incidents involving all vessel flags and types. All UK registered commercially operating craft are required to report accidents/injuries to MAIB. Non-UK Flagged vessels are not required to report accidents/injuries to MAIB unless they are both within the UK 12 mile territorial waters and carrying passengers to or from a UK port. The data included the reported latitude and longitude of the reported position of the incident, with precision of 1.8 nautical miles.

Contact with debris is not considered to constitute a marine accident to a vessel (and therefore is not represented in the data) unless the contact resulted in one of:

Material damage or loss of vessel The vessel needing assistance to reach port The vessel being disabled for 12 or more hours Collision Grounding Significant harm to the environment

A frequency distribution of the number of incidents, excluding collisions with a wreck (not debris), is shown below against the vessel tonnage.

118

1915

10 11

22

48

1 20

20

40

60

80

100

120

140

Number of Reported Incidents vs. Vessel Tonnage

Figure 1: Frequency Distribution of Debris-Related Incidents



This distribution may reflect the greater number of smaller craft in general use, as well as their fragility and size relative to that of the debris. The recent change to include reporting of incidents involving vessels below 100gt will also have influenced the data. The proportion of incidents involving vessels of 10gt or less is 56% (118 out of 210).

The geographic distribution of the incidents is shown for the British Isles region in Figure 2. The distribution is quite even around the UK, and as such there is no indication that any area of the coast should be favoured for surveillance over other areas to prevent a greater number of incidents. There appear to be relatively few incidents in the Irish Sea itself, but this may be an anomaly due to the data collection and reporting systems employed.

This suggests that opportunities to preferentially search in accident ‘black-spots’ are limited.

Figure 2: Geographic Distribution of Reported Floating Debris Incidents

An enlarged version covering the English Channel is shown in Figure 3:



Figure 3: Reported Incidents in the English Channel Region

Only one report suggests a container as the item with which the vessel collided and even in that case there was no certain identification.

Out of 105 incidents:

10 were soft or obstructing items

14 unknown floating object

10 unknown cause of the damage.

30 unknown submerged objects – undefined whether submerged floating or submerged resting on bottom

10 wood

1 possibly a container

20 nothing specified in the description

It would seem that the two reliable categories are large pieces of wood/timber and smaller pieces of debris which go on to block engine intakes or the rudder and cause accidents by debilitating the vessel. The data supports the study assumption of debris types made in section 2.



B Appendix: Indirect Detector Systems

Indirect detection relies on the properties of the environment around the debris responding to a sensor such that the presence of the debris can be detected indirectly from its environment.

Two possibilities for environmental properties have been identified:

The sea surrounding the container An artificial marker, carried by the debris. Artificial markers are discussed in Appendix C of

[RD1].

In Table 5, indirect sensors are summarised that rely on detecting (either actively or passively) changes to the sea environment surrounding the debris.


Microwave (Active) - Radar

Wave patterns are affected by floating objects. By looking specifically at wave patterns it is possible to pick out disturbances and pinpoint potential optical targets. There is a close relationship between algorithms for dealing with small target detection, sea clutter suppression and waveheight analysis. Commercial systems are available (e.g. [RD7] and [RD8]).

Investigate further. Limited by nature of debris

Visible Light The effectiveness of optical detection systems is due in part to the observation of the interaction of the floating debris with the sea (e.g. waves breaking over the debris).

Inherent complement to direct optical detection of the debris. Need to analyse performance relative to radar.

All surveys

Acoustic We speculate that analysis of sonar clutter from the sea surface might reveal the presence of a floating object.

Track improvements in sonar signal processing.

Local survey

IR Similarly the effectiveness of IR detection systems is due in part to the observation of the interaction of the floating debris with the sea.

Will be an inherent complement to direct IR detection of the debris.

Local survey

Over-the-horizon (OTH) radar, sky wave and surface wave

Long-wave HF OTH radars can detect waves over long distances and may offer the possible detection of large objects of debris at long range if they cause large disturbances.

Monitor developments of OTH radar.

Wide area survey

Ultra-Violet Impractical. Do not pursue None

Magnetic (Active)

Not many magnetic materials in the system and hence not effectice.

Do not pursue. None

Table 5: Summary of Indirect Sensors



C Appendix: Glossary

AtoN Aid to Navigation

ECDIS Electronic Chart Display and Information System

EEZ Exclusive Economic Zone

FLIR Forward looking infra-red

GLAs General Lighthouse Authorities

IALA International Association of Marine Aids to Navigation and Lighthouse Authorities

IMO International Marine Organisation

IR Infra Red

Lanby Large Automatic Navigational Buoy

LIDAR Light Detection And Ranging

LPS Local Pinpoint Search

MAIB Marine Accident Investigation Board

MCA Maritime and Coastguard Agency

MIRAS Microwave Imaging Radiometer with Aperture Synthesis

MWR Microwave Radiometer

NAS Narrow Area Surveillance

NVD Night Vision Device

OTH(-SW) Over-the-horizon (Surface Wave) radar

R&RNAV The Research and Radionavigation Directorate

RD Reference Document

ROV Remotely Operated Underwater Vehicle

SAR Synthetic Aperture Radar

SLAR Side-Looking Airborne Radar

TRIZ A problem-solving and analysis tool derived from the study of patterns of invention

UAV Unmanned Aerial Vehicle

VTS Vessel Traffic Services

WAS Wide Area Surveillance