The steps below are comprehensive for the entire workflow of towed camera systems. In many cases, there will be a designated specialist or team to perform some of these steps. Indeed, for heavy deep-tow and complex systems (e.g. JAMSTEC’s deep-tow systems), most, if not all of these steps may be managed by external technicians and engineers. In this case, it is the researcher’s responsibility to ensure that the externally managed workflow is comprehensive and addresses the steps as described in this field manual. This is best done in Pre-Survey Preparations.

Pre-deployment

Risk Assessment

Complete an on-site Workplace Health and Safety risk assessment following agency-specific protocols. A risk assessment should always be completed prior to deploying equipment to ensure the operation can be completed safely. Always adopt a precautionary approach.

Set up and testing

Allow sufficient time during survey mobilisation to undertake system checks, calibrations and testing of equipment and account for unforeseen problems. In most cases it will be possible to complete all system tests and checks within a few hours to half a day. The conduct of pre-start checks should be noted in the trip log and any test failures specifically recorded for later-reference. Detailed settings for each component should be made using relevant operations manuals (e.g. USBL operations manual etc.).

On-deck dry tests should include, but are not limited to, the following checks:

  • On-board storage;
  • On-board power;
  • Cameras, including a review of image quality (colour chart test);
  • Lights and strobes;
  • Seals/o-rings;
  • Recording devices (e.g. computer/s with appropriate software, USB drives, SD cards etc);
  • File copy times for offline recording devices (e.g. GoPro);
  • Winch operation;
  • Sea fastening;
  • Surface communications; and
  • X-Y-Z coordinates from the tether termination to the imaging chip of each camera, altimeter, depth sensor/CTD and transponder.

Wet testing should include checks of the following:

  • Power;
  • Cameras, including a review of image quality;
  • Acoustic tracking system (USBL) and any internal navigation; and
  • Lighting and strobes.

Acoustic tracking setup:

  • Set position of GPS receiver. Differential GPS is recommended as a minimum and is mandatory for repeat site monitoring;
  • Deploy acoustic tracking transceiver (e.g. pole, flange or vessel mounted);
  • Measure offsets of USBL transceiver head to GPS receiver and put offsets into navigation system; and
  • Ensure accurate vessel dimensions are obtained and entered into the vessel plan repository of the navigation software.

Stills camera time calibration

  • Calibrate the stills camera and video feed from GPS in the video overlay relative to UTC time;
  • Ensure all sensor logging systems, cameras, computers have been synchronised to UTC time;
  • Time coding calibration should be applied at the commencement of a survey and checked for consistency at least once a day while the survey is in progress; and
  • Ensure recording media/storage devices are working correctly and review imagery/video.

Pre-deployment checks

  1. Ensure all personnel understand their roles by conducting an appropriate toolbox talk, incorporating risk assessment and appropriate PPE to be worn. See Chapter 1 for further information about risk assessments.
  2. Confirm with the vessel Master that GPS tracks for the proposed deployments are accurate and the order of transect sampling is clearly communicated.
  3. Discuss the desired target location and the feasibility of deploying at that location. Main items to take into account are:
    • Terrain. To minimise the risk of a deployment almost all tows will be conducted on either a flat or downward sloping seafloor. This will reduce the chance of the camera hooking up and allow for the platform to fly out into deeper water if there is a winch failure. Consider if there are any large ridges, boulders, drop-offs, etc. along the proposed tow route as with minimal forward vision, 10 m or less, there is not a large margin for avoidance.
    • Weather/sea state. When the camera is flying along the ocean floor, the ship will need to travel at ~ 0.5-1ms-1. This can limit the manoeuvrability of the ship and depending on the direction of the prevailing wind and swell, is not always possible on a particular heading. As the sea-state and swell can affect the ships manoeuvrability when travelling at low speeds it is essential to regularly check the weather forecast to ensure the sea state is acceptable and the platform can be safely deployed and retrieved.
    • Depth. Be aware of the depth limitations of the towed body and the wire that the platform is deployed on.
  4. The vessel Master must approve each deployment and communicate with crew prior to launch.
  5. Prepare tow body on deck and ensure only essential personnel participate in its preparation and deployment.
  6. Check for correct operation of cameras and lights (check explicitly for miss-timing between image capture and strobe firing) and winch including watertight seals, power requirements, hydraulic power and hoses, time synchronisation (PC, USBL, camera systems) and recording media. (e.g. check all recording systems are synchronised to UTC time).
  7. If necessary, attach the USBL beacon to the frame and check that it is operational.
  8. Perform laser alignments as per manufacturer’s procedure.
  9. Inspect the platform for any deterioration in cables and cable ties, ensure frame nuts and bolts are tight and all equipment mounts are secure.
  10. Ensure all connections to pressure housings and equipment are tight and secure.
  11. Ensure the winch clutch or load relief mechanism is adjusted to the correct tension prior to initial deployment.
  12. Once all instruments are confirmed working, handclap within an overlapping field of view of all cameras.
  13. Inform the bridge and deck you are ready to deploy and wait for confirmation from the bridge that the ship is at deployment speed and is approaching the start of the survey line.
  14. Ensure the nominated winch driver is in the operations room with a functional and fully charged winch remote control, set to the specified channel.
  15. Ensure that all staff are familiar with the seabed ‘hook-up’ procedure (see Section 7.5.4) and how to respond should it occur before commencing deployment.

Deployment

  1. Run the towed body termination through the large block on the centre of the A-Frame and make sure there are no twists in the wire.
  2. Following the signal to deploy from the vessel Master, use the winch and A-Frame to lift and guide the tow body from the deck into the water as the vessel begins tracking towards the start of the transect line.
  3. Minimise the time taken from when the tow body is let out of reach, to when it is lowered in the water, so as to reduce potential swing and impact against the vessel.
  4. Deploy the platform into the water.
  5. Check for cable loops or problems at the surface while the tow body is being lowered into the water before losing sight of the platform below the waterline.
  6. Once in the water, lower the camera to an appropriate depth where the system can be checked, turn everything on, including the lasers, and check that all is functional. If recording ascents/descents through the water column, perform system checks just below water surface
  7. Check the USBL is receiving and the ship and platform are indicated on the bathymetry overlay.
  8. Confirm that the USBL data are being logged.
  9. There are several factors that affect how much wire out is required for the towed camera system to reach a target depth. These include: vessel speed through the water, payout/haul in speed, and cable diameter, package drag and weight. Determine the appropriate wireout ratio specific to the vessel and its speed, noting that ocean currents can affect this ratio.
  10. Continually monitor the descent rate at separate intervals, checking the ratio of wire out to depth. This can impact on when the platform will actually reach the required depth and the location this will be. If the ratio is too high, there is the possibility of not reaching the required depth before passing over the target area. If the ratio is too low, the platform will reach the required depth well before the target area. The platform descent rate and estimated touchdown location needs to be continually monitored for a successful tow.
  11. Maintain active communication with the Vessel Master and other crew/staff/technicians by providing clear, suitably loud and concise instructions/updates on the status of the equipment in water. Crew/staff/technicians to acknowledge they have received and understood instructions with clear, concise, suitably loud response(s).
  12. To mitigate any positional errors, it is important to carefully monitor the ship speed and deployment rate to an appropriate ratio. If you have reached the seafloor too early, try to resist speeding up the ship. This will cause the platform to rise when speeding up and fall uncontrollably when slowing down again.
  13. Continue descent to a pre-determined height above the seafloor (e.g. 2–3m) and try to maintain this height throughout the tow using the winch remote control. Record/document the time the target depth (i.e. altitude) is reached (typically this is at the start of the transect where data collection begins, unless the objective of the work includes water column imagery acquisition during descent). Note: hauling in cable onto the winch or paying out cable has an immediate effect on the camera platform height above the seafloor; however, the degree of change on height above bottom is in relation to the cable angle, which is determined by the vessel’s speed and current.
  14. Confirm still photos are being taken and video feeds are being recorded where possible (e.g. recording indicators, hard drive operating).
  15. Confirm the timecode being embedded is GPS-time accurate.
  16. If employing real-time annotation, record the time and position of the camera on the seafloor (See Pre-Survey Preparations).
  17. While maintaining a consistent flying altitude above the seabed, the co-pilot needs to continually check the camera feeds to ensure all footage is being recorded and anticipate the need to come up on the winch so as to avoid approaching obstacles and minimise the chance of a seabed hook-up, and review.
  18. Monitor sea conditions during deployment to maintain a safe working environment.
  19. Consider aborting operations if sea conditions are marginal, visibility is poor or any fault develops that may interfere with the towed camera system operation.

Retrieval

  1. Continue deployment until advised by the watch leader/chief scientist that enough footage has been recorded.
  2. When the survey line is complete or if the transect is being aborted, advise vessel Master of intention to retrieve the tow body. Record/document the time the target depth (i.e. altitude) is left (usually this is at the end of the transect where data collection ceases, unless the objective of the work includes water column imagery acquisition during ascent).
  3. When close to the surface ask the officer on watch to confirm the ship is on the best heading for retrieval and hand over operational control to the deck crew.
  4. Watch for the approach of the tow body near the surface ensuring only required personnel near the open transom.
  5. If possible, turn off lasers and lights before reaching the ocean surface. If lasers are self-contained then ensure staff are wearing protective eyewear.
  6. Use winch and A-Frame to guide tow body back onto deck with smooth winch and A-Frame control inputs.
  7. If safe to do so, ensure the crew grab hold of the tow body as soon as the tow body leaves the water, so it can be guided safely away forward of the transom and lowered to the deck. Alternatively from small vessels, boat hooks with loaded snap-buckles on tether-lines can be attached just below the surface before the tow body leaves the water. Ends of tether-lines can be pre-fed through A-Frame cleats to control the ‘swing’ of the tow-fish as it rises out of the water and is brought up on deck.
  8. Once clear of the water, stop all recordings, and turn all cameras, sensors and power off.
  9. Rinse the towed platform frame and all camera(s)/sensors with fresh water.
  10. If attached, remove the USBL beacon and recharge.
  11. Check and rename video footage, still camera photos and log files and complete Metadata Information sheet. Archive all data files (imagery, sensor data, metadata) on a drive that is backed-up regularly (see Section 7.5.6 On-board data processing and storage).

Seabed hook-up procedures

Hook-up of the tow body is always a possibility with the ideal altitude for capturing quality still images close to the seabed. The following procedures should minimise the potential of a hook-up occurring and lower the potential of damage to the tow body or total loss:

  1. Communication link between tow camera winch station and bridge should be maintained at all times (e.g. VHF or intercom).
  2. Bridge should monitor video feed from tow body while undertaking tows
  3. At the first sign of a hook-up (e.g. video image stationary over seabed), ensure the forward speed of the vessel is backed off to reduce tensile load on cable.
  4. With the crew monitoring the position of the cable and directing the vessel Master with regard to the position of the cable, the vessel is to maneuver back to a point directly over the hook-up point to see if the tow body can be freed.
  5. Cable tension should be taken up by the winch to ensure no loose cable enters the vessel propellers.
  6. If the initial retrieval attempt from overhead fails, various points of the compass should be tested by the vessel to pull the tow body off the seafloor, using only the winch to ensure enough cable remains.
  7. If all options for retrieval have been exhausted the cable must be cut at the shortest possible point and the position recorded with GPS. Note: With a live video feed there is power to the cable so due consideration must be given to ensure that all power to systems and deck boxes etc. are off prior to cutting the cable.
  8. A substitute tow body and cable would need to be prepared for continuance of survey operations.

Operation completion

Prior to any vessel movement or engine start-up, operators should check the following:

  • All equipment is clear of the water, including acoustic tracking equipment;
  • All gear is safely stowed and powered down where appropriate;
  • Any servicing that requires the vessel to be stationary is completed;
  • When the towed camera team is satisfied it is OK for the vessel to move on, an “All Clear to Move” command should be given to Vessel Master; and
  • Data collected from previous tows should be checked for integrity prior to deploying the towed system on further tows.

Onboard data processing and storage

Consider navigation, data logging, real-time quality control, and display. A range of specialized marine image annotation tools have been developed worldwide to facilitate real-time underwater image analysis (reviewed in Gomes-Pereira et al. 2016). These tools generally consist of a graphical user interface, with a video player or image browser that recognizes a specific time code or image code, allowing events to be logged in a time-stamped (and/or geo-referenced) manner . Examples include: Adelie, Customizable Observation Video imagE Record (COVER), Frame-Grabber, Ocean Floor Observation Protocol (OFOP), SeaScribe/Seatube, Video Annotation & Reference System (VARS), VideoNavigator, Jason Virtual Control Van (web browser logger on a ships network allowing for digitally logging comments and observations during capture), CampodLogger. These software packages integrate data associated with video collection, the simplest being the position coordinates of the video recording platform, with more advanced packages allowing the input and display of data from multiple sensors or multiple annotators via intranet or internet.

Name data files according to established conventions. File naming conventions are important for ensuring both efficient and effective management of field data and its integration into appropriate data management repositories. It is important to note that these conventions will differ among agencies and academic institutions.

For example, CSIRO uses ‘Platform_Camera_Survey_deployment_YYYYMMDDThhmmssZ_other’, while NSW Department of Planning, Industry and Environment uses ‘Organisation_Platform_Survey_Locale_Site_ Transect_date_starttime_imagenumber’. Note: ‘camera’ is specified as many towed platforms have multiple cameras (e.g. video and stills, stereo cameras, port and starboard cameras).

Ensure accurate recording of metadata. Metadata are descriptive data sources composed of information that may be used to process the images or information therein (Durden et al. 2016a). While it is important to follow agency specific protocols for capturing metadata, it is also essential that metadata are of sufficient detail to satisfy conformance checks for subsequent data release via AODN (See Table 7.2 for sample metadata sheet). Metadata should also contain survey-specific information such as camera specifications and imagery file naming protocol, as well as product lineage. Minimum data for each image/frame capture should include georeferenced information, as well as any other related sensor information and (where appropriate) real-time characterisation details:

  • Campaign (i.e. Survey identifier)
  • Station/event number
  • Platform
  • Latitude and longitude (WGS 1984 in decimal degrees [Recommended])
  • Altitude
  • Depth
  • Time and date stamp
  • Platform and/or vessel motion (roll, pitch, heave)
  • Metadata from other sensor data (see example below, CSIRO data file headers)
  • Precision details (e.g. type of navigation system used and its associated errors)
  • Data provenance

Example Video (MNF):

Retrieval of Floreat Shallow Towed Video on survey LN2018_V02, deployment 012, at 15:25:01 UTC, on the 6th of June, 2018.

FSTV_LN2018_V02_012_20180606T152501Z_RETRIEVAL.json

The json file is processed into flat, 1 second csv, with an identical name:

FSTV_LN2018_V02_012_20180606T152501Z_RETRIEVAL.csv

Example Stills (MNF):

Digital Still files are renamed and placed in a folder identifying its site/operation number. The date/time stamp is taken from each still .exif and a script or program is written to take this data, plus data from the log file to do this batch renaming.

FSTV_LN2018_V02_012_20180606T152501Z_00001.jpg

Quality control. Once the towed camera transect is complete, it is good practise to download associated raw imagery and positional data. Imagery and associated position data should be checked to ensure no failures have occurred, including but not limited to the following:

  • Mis-timing between image capture and strobes (i.e. dark/black imagery)
  • Failure of camera/s
  • Failure of positional logging

Backup data. This is necessary to ensure all data collected in the field are safely returned and securely backed-up at host facilities, prior to final quality control and public release. Onboard copies of data should be made as soon as practically possible following acquisition. It is recommended that all data be backed up on a RAID or a NAS that contains built-in storage redundancy in case of hard-drive failure. A duplicate copy of all data onto external hard drives or LTO tapes for transportation back to host facilities is [Recommended].

Table 7.2: Sample field datasheet to record metadata (i.e. deployment or event data) from each towed camera deployment.

Gear in water Gear on bottom Tow speed Wire out (length) Wire out (angle) Gear off bottom Gear out of water Notes
Tow ID Long Lat Time Long Lat Depth Time Long Lat Depth Time Long Lat Time