The sustainment of the IMS Hydrophone Hydroacoustic Network of the CTBT

Summary

This presentation outlines the sustainment strategies, challenges, and technological innovations for the hydrophone-based hydroacoustic network of the CTBTO International Monitoring System (IMS). It addresses failure causes such as underwater landslides, near-shore cable degradation, and electronics obsolescence across various remote stations including HA01, HA03, and HA08. Solutions presented include hybrid-modular design for underwater node repair via ROVs, shore cable protection, and upgrades to Central Recording Facility (CRF) electronics.

Title Slide

SnT 2021 - CTBT: SCIENCE AND TECHNOLOGY CONFERENCE CTBTO PREPARATORY COMMISSION Poster No.: P4.4-276

The sustainment of the IMS Hydrophone Hydroacoustic Network of the CTBT Georgios Haralabus, Jerry Stanley, Mario Zampolli CTBTO IMS/ED/HA [email protected] PUTTING AN END TO NUCLEAR EXPLOSIONS | CTBTO.ORG

Abstract

ABSTRACT Hydroacoustics is the only verification technology of the International Monitoring System (IMS) of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) to be fully certified. Five T-phase stations and six hydrophone-based hydroacoustic stations monitor the world oceans 24/7 for signs of nuclear explosions. Hydrophone stations comprise triplets of underwater microphones, called hydrophones, suspended hundreds of meters below the sea surface and cabled to shore with electro-optical cables, providing near real-time hydroacoustic data to the International Data Centre in Vienna, Austria. Installing the six hydrophone-based hydroacoustic stations in some of the most remote places on the planet constituted a major engineering accomplishment – sustaining or repairing them turns out to be equally, if not more, challenging.

Failure causes include natural phenomena, such as underwater landslides which damage underwater segments of cables, degradation of cable protective material in the near-shore areas, and obsolescence or malfunctioning of shore equipment. This poster summarizes the on-going sustainment projects of the IMS hydrophone hydroacoustic network though re-establishment solutions of damaged sections, risk mitigation studies and external aggression protective measures, innovative modular solutions for easy of repair of underwater components and enhanced resilience together with protective measures for onshore electronics.

Introduction

INTRODUCTION - The IMS Hydroacoustic Network

➢ (Grey boxes) 5 T-phase stations: near-shore seismometers, which record waterborne hydroacoustic waves coupled upslope into the earth’s crust.

• HA02, Queen Charlotte Is. (Canada)
• HA06, Socorro Is. (Mexico)
• HA05, Guadeloupe Is. (France)
• HA07, Flores Is. (Portugal)
• HA11, Wake Island (USA)

➢ (White boxes) 6 Hydrophone stations: moored hydrophones pick up hydroacoustic waves in the water column.

• HA03, Robinson Crusoe Island (Chile)
• HA10, Ascension Is. (UK)
• HA09, Tristan da Cunha Is. (UK)
• HA04, Crozet Is. (France)
• HA08, BIOT/Chagos (UK)
• HA01, Cape Leeuwin (Australia)

Acoustic coverage provided by the IMS HA hydrophone stations (K.D. Heaney, R.L. Campbell (OASIS Inc., USA), presented at International Hydroacoustics Workshop, CTBTO, (June 2015).)

Methods - Sustainment Strategy and Depth Profiles

METHODS Key Drivers:

• condition of equipment
• technological obsolescence/advancements

Methodology: Three distinct components of a Hydroacoustic Hydrophone station – treated differently:

1. Under-water cable and triplet:

• Methodology: run-to-failure (failure meaning when the station becomes incapable of providing useful data); Hybrid modular design.
• Notes: Current experience and SoH factors indicates that its lifetime most likely will exceed 20 years. Cost of replacement expensive, so wish to maximize use of current assets.

2. Near-shore cable and cable landing:

• Methodology: Inspections on a 3-5 year cycle – more frequent as necessary; Repair as required.
• Notes: Cable in the near-shore is the most subject to rough conditions. Inspect, repair/replace extends the life of the full UWS.

3. Central Recording Facility:

• Methodology: Frequent inspections by SO and repairs undertaken; Technological refresh of computer hardware and software.
• Notes: Regular inspections, repairs and technological upgrades extends its life.

Hydrophone Station Details:

• HA01: W | Water depth: 1550 m | Hydrophone depth: 1100 m
• HA03: N | Water depth: 1866 m | Hydrophone depth: 824 m
• HA03: S | Water depth: 2071 m | Hydrophone depth: 830 m
• HA04: N | Water depth: 1310 m | Hydrophone depth: 541 m
• HA04: S | Water depth: 1309 m | Hydrophone depth: 535 m
• HA08: N | Water depth: 2300 m | Hydrophone depth: 1250 m
• HA08: S | Water depth: 1800 m | Hydrophone depth: 1350 m
• HA10: N | Water depth: 2000 m | Hydrophone depth: 850 m
• HA10: S | Water depth: 1700 m | Hydrophone depth: 850 m
• HA11: N | Water depth: 1400 m | Hydrophone depth: 750 m
• HA11: S | Water depth: 1150 m | Hydrophone depth: 750 m

Methods - Hydroacoustic Station HA08 (Diego Garcia)

METHODS Hydroacoustic Station HA08, Diego Garcia, BIOT/Chagos Archipelago, UK (operated by the USA)

The Hydroacoustic Station, HA08 at Diego Garcia was installed in the year 2000 and worked flawlessly until March 2014 when the H08N segment stopped operating due to a cable fault localized at about 190 km from Diego Garcia shore.

Detail of the undersea topography in the area of the H08N cable break (marked by a red star). The black line shows the route of the hydroacoustic station fibre-optic trunk cable. The colour-scale represents the water depth. Undersea terrain model from US Naval Oceanographic Office.

The IMS/ED hydroacoustics team has conducted a thorough investigation into a viable solution for the damaged north segment of HA08, in conjunction with the independent experts.

Methods - Hydroacoustic Station HA01 (Cape Leeuwin)

METHODS Hydroacoustic Station HA01, Cape Leeuwin, Australia [see also ePoster P4.4-323]

The nearshore cable inspections conducted in 2018 and 2019 identified failing cast iron split pipe protection in the very nearshore. This section of split pipe being subject to highly energetic surf action, dynamic sand movements and accelerated corrosion.

IMS/ED has identified two options for cable sustainment: a) Replace the failing nearshore cable with the application of new split pipe protection. b) Replace the failing nearshore cable using a Horizontal Directional Drilling approach.

As more frequent and strong lightning strikes were observed in the vicinity of the HA01 CRF, the CRF will be upgraded with a lightning protection system in-line with the CTBTO best practices. (Figure shows HA01 CRF, VSAT antennae, GPS antenna, BGAN antenna, and Shore vault).

Methods - Hydroacoustic Station HA03 (Robinson Crusoe Island)

METHODS Hydroacoustic Station HA03, Robinson Crusoe Island, Juan Fernandez Archipelago, Chile

Cable Lengths: North – 33.3 km, South – 49.1 km

The seas in the Bay are highly energetic and particularly in the surf zone the split pipe protection is exposed to high dynamic loads. Consequently, these shallower sections of split pipe, up to a depth of ~30m, should be routinely inspected for damage by divers and remedial actions undertaken as required.

The nearshore cable at HA03 is exposed to anchor damage risk from fishing, cruise ships, and cargo ships operating in and around Cumberland Bay. A navigational marker buoy equipped with a flashing light is deployed to mark the cable route to mitigate the risk of ships accidentally damaging the cable. The buoy and its moorings should be maintained on a regular basis.

Methods - Modular Design for Sustainable Stations

METHODS Modular design – Next generation sustainable hydroacoustic stations [see also ePoster P1.3-270]

❑ Modular Design Studies conducted jointly with Independent Experts (IE) to enhance IMS HA Station Sustainability: ▪ Maintain the current linear, all-connected, sequential and robust deployment method while ▪ Enabling replacement of failed IMS HA Node Components without replacing the entire Underwater System Triplet.

❑ Proposed solution: Hybrid-Modular design of a Node component, called the Modular Latch, that incorporates underwater wet-mate connectors able to be plugged/un-plugged directly underwater using a Remotely Operated Vehicle (ROV).

ROVs are equipped with suitable robotic arms, which can enact an underwater repair by disconnecting failed components and replacing them with new ones.

Methods - Enhanced Resilience of HA Station CRF Electronics

METHODS Enhanced resilience of the cabled HA station CRF electronics [see also ePoster P4.3-267]

Presently, this system remains vulnerable to data loss in the case of SSI malfunction, issues with the CRF network, satellite link or GPS Week Number RollOver (WNRO).

On-going upgrade of CRF electronics:

• upgraded DDFI to continuously save in a local buffer all UWS data and DDFI diagnostic information
• enhance the capability of the DDFI’s and HA SSI’s, in order to allow remote access to this local buffer
• upgrade SSI/processing to temporary mediate (patch) unforeseen GPS rollover issues and in the medium term upgrade DDFIs’ software (and GPS receivers where needed) to become resilient to future WNRO’s.

(A schematic illustrates data-flow in the CRF of a cabled HA station: fibre-optic cables / raw digital data from UWS -> L3 MariPro DDFI -> CTBTO SSI(s) -> Authenticated CD1.1 to satellite router(s); along with GPS time-stamp, electrical cables/shore control, alarms, and UPS).

Results

RESULTS ❑ Surveys, inspections, enhancements and repairs to the hydroacoustic network are being undertaken/scheduled with the intent to maximize station availability – major projects related to HA01, HA03, HA04 and HA08 are in the pipeline for the upcoming strategic planning cycle.

❑ A novel modular design solution to facilitate individual underwater component replacement is under evaluation and testing.

❑ Improved HA station CRF electronics are of paramount importance to safeguard data availability, thus supported by ongoing enhanced capability actions.

Conclusions

CONCLUSIONS ❑ The IMS hydroacoustic network is unique in a global scale in terms of: ▪ Operational readiness level ▪ Spatial and temporal coverage of the Oceans ▪ Data sharing

❑ The safeguarding of its operability and the protect this extraordinary investment requires: ▪ Maintaining the periodic sustainment schedule to avoid failures, especially in the nearshore underwater segment ▪ Stay abreast of new technologies and concepts to facilitate resilience and curb maintenance costs ▪ Preserving a wide range of technical skills to protect this multi-faceted network and preserve high data availability.