From Land to Sea. UXO detection surveys in the intertidal and nearshore environments. THS UXO Survey Seminar 19 th June 2015 David Rider MSc

Transcription

1 From Land to Sea UXO detection surveys in the intertidal and nearshore environments THS UXO Survey Seminar 19 th June 2015 David Rider MSc

2 Outline

3 3 Introduction Welcome Company Overview What is the intertidal zone. Land Techniques and Equipment Case Studies The Gap Survey Design Lessons Learned The Future

4 Introduction David Rider MSc

5 5 David Rider MSc Project Geophysicist with Bibby HydroMap Ltd. for over 5 years Bangor University Applied Marine Geosciences Masters Hydrographic Surveyor for 2 years Background in Outdoor Education and Water Safety

6 Introduction Company Overview

7 About Bibby HydroMap Committed to Quality and Innovation Personnel Bibby HydroMap employs over 100 personnel with a wealth of experience and expertise covering the disciplines of hydrography, engineering geophysics, marine geotechnics, engineering geology, oceanography and maritime archaeology. Established in 1997 Since 1997, we have worked closely with clients from the oil and gas, offshore renewables, submarine cables, ports and harbours, aggregates and utilities industries to provide efficient and cost-effective survey services. Own Fleet and Equipment With a focus on innovation, we invest in the custom-build survey vessels and the latest offerings from industry leading manufacturers.

8 Survey Services 8 A summary of our core offering Multibeam Bathymetry Side Scan Sonar Sub-bottom Profiler Multichannel Seismic UXO Geotechnical Sampling

9 What is the intertidal zone?

10 Intertidal Zone 10 No man s land, not quite marine, not quite land. Intertidal zone (noun) the area between the land and sea that is covered by water at high tide and uncovered at low tide. Dictionary.com Highly Changeable Tide cycle, Springs and Neaps Weather Accesses Time

11 Muddy Different Sediments Wet Creeks Beach Slope Vegetation

12 Land Techniques and Equipment

13 13 Hand held magnetometer survey Geometrics G858 Mag Mapper Industry Standard Rapid sampling rate 10Hz Very high sensitivity Portable Caesium vapour magnetometer Can be set up with 2 sensors as either a vertical or horizontal gradiometer. RTK DGPS compatible so topography data can also be collected. Pros - Collects any where a human can go. Ideal for small survey areas Cons - Slow even with a small array of 2 sensors. Lines ideally need to be set out and very hard to check coverage on site.

14 14 The Land Ship approach Combination of: ArgoCat 8 wheeled ATV Geomatrix s GEEP survey platform 4 x G880 Caesium vapour magnetometers CNAV 3050 Real time PPP QPS QINSy Pros- Increased coverage, More productivity, Real Time QC, Accurate positioning and safer Cons- Not suited to small areas. Limited by terrain.

15 15 Argo Cat The Argo Cat ATV is an 8-wheeled, independent drive vehicle and has a fully marinised engine and drive system, which is steered by a simple push-pull braking lever system and a twist grip accelerator. The vehicle has a standard tow bar to pull sleds and carts. Weight: 0.31 tonnes Ground Pressure: psi Max Gradient: 45 degrees Speed: 20mph(Land), 2mph(Water) Capacity: for 6 persons or 1 geo, driver and a shed load of kit!

16 16 Geophysical Exploration Equipment Platform GEEP Geophysically invisible tow sledge Allows 4 G880 caesium vapour magnetometers at 1m spacing. Self concatenating Interface box- containing a heading, pitch and roll sensor. Multiplexer Kevlar reinforced tow cable carrying power and data back up. DATEM- powers the GEEP systems via battery and de-coding Controlling laptop running QPS QINSy CNAV 3050 using C-Nav corrections real time PPP or Leica RTK receivers using Leica Smart net. Post processing the CNav 3050 data with PPK techniques can give a topo surface.

17 Case Studies East Coast Pre lay cable landing UXO Survey

18 18 Cable route landfall Intertidal, beach and salt marsh terrain High probability of UXO Detailed magnetometer and topographic survey- 50m corridor along a route with 1m mag spacing. Requirements provided by a UXO consultant. Surrogate trial required to prove methodology

19 19 Surrogate Item trial Surrogate trial required to prove methodology Trial steel cylinders to represent suspected site UXO Trial items buried to approx 30cm Processing in Oasis Montaj Items calculated position within ± 0.5m of recorded position

20 20 Magnetic anomaly enhanced Data processed using Geosoft Oasis Montaj industry standard software Navigation QC d - Raw total field data de-spiked - removal of long wavelength component using Oasis non-linear filter No need for diurnal corrections or base station data, Regional geological effects removed and short wavelength anomalies enhanced

21 A head scratcher! 21 Suggestions ranged from processing artefacts to pipelines, fences, wires and even ancient field boundaries! Anomalies clear even in raw data not artefact Anomalies discreet, not continuous not fences/pipelines/wires Anomaly strengths of the order of nT too strong to be related to post holes/field boundaries

22 22 Interpretation No clues from aerial photographs Admiralty charts mention numerous stakes Locals also mentioned poles WW2 tank traps or other beach defences? Answer found through internet search! Archaeological Research Services Ltd - North West Rapid Coastal Zone Assessment undertaken for English Heritage 2 This block, with it s [sic] lack of urban conurbations, contains very little archaeological evidence from the World Wars, although there were extensive antiglider obstacles placed within [the local area] and mapped as part of the APM exercise for this project. These appear to have been long since swallowed by the shifting sands. 2

23 23 Anti-glider defences as placed by German troops in France (1944) 3 Remains of posts at Burntisland Bay, Scotland 4 Poles still in situ at Culbin Sands, Scotland 1 Wooden stakes used extensively in WW2 as anti-glider traps Set in reinforced concrete Barbed wire strung between poles

24 Case Studies Normandie 3 Pre lay cable landing UXO Survey

25 Normandie 3 Cable UXO Survey 25 Since the failure of the Normandie 1 Cable in 2012 increasing amount of the electricity is needed to be produced on the islands of Jersey and Guernsey. Normandie 3 will allow cheap electricity from France and in Guernsey's case increase its imported supply from 30%to 90%. Normandie 3 is a 32km long HVDC cable from Armanville to Gorey

26 26 Armanville Plage, Normandie, France Flat and sandy beach part of Rommel s Atlantik Wall Fast tides and creeks 4 hours of work Cable route, barge set down, anchor locations

27 27 Ideal Conditions for the Land Ship method Had to be careful with daylight and tide came in fast! Difference in springs and neaps Not all areas of the site were accessible with the GEEP G858 data spliced in. Day two and a local dog walker finds this! A good reminder as to why this survey was needed!

28 28 Creeks! Need for good communication with the boat team. Land support Example of QINSy helm

29 29 Gory Beach, Jersey Same hard compacted sand. The public and their four legged friends! High likelihood of UXO

30 30 WW2 German garrison beach defences Thought to have been cleared. Possible WW1 French artillery shell also found. Beach data, Processed in the same as before also depths and weights calculated from AS grid in Oasis Montaj Mag survey in a compound?

31 The Gap Very Near Shore Marine UXO Surveys

32 32 Marine Magnetometer survey Geometrics G882 Marine Caesium Vapour Magnetometer Industry Standard Rapid sampling rate 10Hz Very high sensitivity Pros Can be combined with an altimeter, light weight - can be towed from a RIB Cons Needs to be towed in water! Very sensitive needs to be kept 2-3 time boat length

33 33 Kentish Flats Extension Acquired with G858 and G823 hand held sensors. Coverage needed to meet with existing marine data Required a boat survey in the surf zone POSITIONING The most important factor of any marine geophysical survey. 5m water at the maximum. To noisy and shallow for USBL. Too dynamic for GPS on a floating sled Layback can work!

34 34 RIB towing a G882 Key to good layback navigation Good communication between survey crew and the helm Always go into the dominant current and try and get cross lines RTK GPS with receiver as close to the TP as possible. Use a navigation package like QINSy with heading and level inputs (accurate heights) Lowest towing angle as possible KISS we only used one fish to get the best position from it. Expect Infill so reduce Line spacing!

35 35 Not just Magnetometers On this site there where close to 2000 mag anomalies Side scan sonar data for the marine and topography and photos proved invaluable for interpreting the site. Beaches can be cluttered!

36 Survey Design What is needed and where

37 37 Survey Design Unlike most other types of marine survey UXO surveys need to be targeted. Active as apposed to passive surveys. What are you looking for? What is the risk and who to? What level or accuracy is needed? These will all drive survey design! Beaches can be dangerous!

38 38 UXO consultants, clients and survey contractors can provide this information but it has to be a two way street. GOOD COMUNICATION IS KEY Client Requirements Client requirements: Anchor locations, ship laid or man dug Corridor width UXO Threat: Line Spacing and type of sensor Survey Design Survey/Environmental limitations: Which techniques are needed to full fill the above. Can it be done safely with the type of beach. UXO Threat Survey/Environmental Limitations

39 Lessons Learnt Conclusions

40 40 Every beach is different! Always recce the beach Walk the route if needed Local knowledge RNLI What does the tide do can you be cut off? Communication NEVER WORK ON RISING TIDES! Plan for the worst and hope for the best

41 The Future What s next for near shore survey

42 42 Drones Legislation? Endurance? Public preconception/safety? Hovercrafts Legislation? Weather restrictions high winds and line keeping? Access?

43 Questions