Image courtesy FBI Dive Team

DIRECTING DIVERS with SONAR Training Module

Presentation © STS

This training module provides information specific to using sonar in support of diving operations.

It includes:

Disclaimer Active sonar and diver safety

Dive planning Monitoring the underwater worksite

Underwater communications Scanning sonar tripod deployment

Diver prosecution of a target Umbilical management

Side-scan sonar and directing divers

Diving operations must be completed in accordance with all Federal and State (Provincial) regulatory codes, including (but not limited to) workplace, Health and Safety, and Dive Agency standards.

The information contained herein is to be used as a guide to assist diving operations. If any situation

appears unsafe, it is your responsibility to immediately address the problem(s) and establish

and maintain a safe working environment.

IMPORTANT SAFETY INFO

Anchor cables attached to floating dock slips at a marina were hazards identified during a body search. The dive was

planned (and monitored in real-time on the scanning sonar display) so that the

tethered diver never risked entrapment by swimming

under the anchor lines.

Anchor cables

Concrete mooring blocks

Crab trap The safest place for a diver is on the surface. Utilizing

scanning sonar before the diver descends can identify potential

hazards and provide critical information for effective dive

planning.

25 m range

Use the information from the sonar image to assist dive planning.

PLAN the DIVE; DIVE the PLAN

Sonar identified a potential cable hazard during a police training dive. The diver was carefully guided to the target, and by feel in

zero visibility, confirmed it to be a tangled mess of barbed wire.

Sheet pile wall

diver

Not only can the sonar be used to locate targets of interest, it will also locate potential hazards.

USE the SONAR to IDENTIFY POTENTIAL DIVER HAZARDS

IMPORTANT OPERATION’S TIP

Divers must be in communication with the surface via either hardwire or through-water coms to maximize the efficiency of using sonar for this

application. The dive tender needs to hear diver directions.

Scanning Sonar tripod used by Utah State Police

Tripod used by US Navy during recovery of the Space Shuttle Columbia

Weight used to stabilize the

gimballed head in current.

Orient the 0-degree of the head to an alignment mark on the top of the tripod.

SCANNING SONAR TRIPOD DEPLOYMENT

Diver

Diver’s acoustic shadow

Rig

Pipeline

Diver

Diver’s umbilical

30 m scale range

Data courtesy Fugro Chance Inc., Lafayette, La

Use the diver’s umbilical to determine the direction the diver needs to move to prosecute a target of interest.

MONITOR the DIVER’S UMBILCAL

wind directionHave the diver face their umbilical and move left, right, forward or backward as directed by the sonar operator. Move the diver is steps or arm lengths and not distance measurements. Keep the diver from going under the anchor line/chain.

Anchor the vessel during diving operations.

target

Use hard-wire or through water communications between the surface and the diver; line pull signals are not effective.

When prosecuting small targets avoid positioning the diver between the sonar and the target.

SHADOWING the TARGET

Diver

Pipeline

50 metre range

Diver’s stage

Rig

Before directions are given, instruct the diver to face their umbilical. Direct the

diver to then move left, right, backward or forward as required. Have the diver

confirm that distance has been completed before issuing new distance

and heading instructions.

Ensure the diver’s movements do not put them in a position so as to block the

target view.

Observe the diver’s umbilical and ensure they work one side of the tripod

at a time (in this case the side of the yellow line). Recover the umbilical and,

if required, instruct the diver to then move to the opposite side (red line). It is important that the diver never wraps

their umbilical around the tripod.

Data courtesy Fugro Chance, Inc., Lafayette, La

IMPORTANT SAFETY INFO

In addition to monitoring the position of the diver’s umbilical to the sonar cable,

make sure as to not position the diver or diver’s umbilical under the anchor line of the support vessel. In the event that the anchor is dragged the umbilical will likely

be free and clear.

MONITOR the DIVER’S UMBILCAL

B

Diver

A

When guiding a diver take several scans to establish which are bottom targets versus those in the water column. Fish air bladders make excellent specular reflectors and can be identified as they move from scan to scan. These two images (taken approximately one minute apart) show that a significant number of targets have moved. Larger crabs can also be mistaken for fixed targets and prove to be elusive if the sonar crew is working ahead of the dive team.

MID-WATER TARGETS

The small boat in the 3 o'clock position is large enough that the diver can be directed to it from any angle without concern of entirely blocking the boat with the diver’s acoustic shadow. The other target is a very small collapsible anchor; only the shank is sticking above the mud line. In this case it is prudent to position the diver so that the target is

never shielded from the sonar’s view.

4.5m (14.3') car top boat

Diver

Collapsible anchor

MOVING DIVER to TARGET

Directing deployed divers in real-time with side-scan is dangerous. Mark the target (as per the side-scan procedure discussed) and have the divers conduct a circle search.

SIDE-SCAN and DIVERS

If side-scan is used for the search, mark the target then use scanning sonar to direct the divers in real-time.

TARGET MARKERS

End

Directing Divers with Sonar