Since the seventies those who wished to have photographic quality records of inspected subsea installations have been using traditional wet-film technology adapted for underwater use. Traditionally these were either diver deployed or mounted on an ROV and triggered remotely.
On remotely operated vehicles video cameras were used to assist framing the stills image but parallax error was inevitable due to the offset of the two cameras. The TVP (Television Photographic) camera solved this problem by using an SLR concept whereby a video camera viewed through the same lens as the photographic camera by means of a moving optical prism.
Once the film image had been taken it was not possible to ensure that it was properly exposed and in focus, although in the more sophisticated cameras such as the TVP, bracketing was used in an endeavour to minimise exposure errors. Any faults in complex mechanical film wind mechanisms were not discovered until the camera was back on the surface meaning that inspection jobs would often have to be repeated. Until the film was developed, in dark rooms that normally accompanied the cameras offshore, the vessel could not leave the worksite lest the work had to be redone. Engineers capable of analysing information on the photographs had to be on board in order to ensure that the appropriate information had been obtained.
With the advent of digital cameras all of the above drawbacks have been overcome.
Photographic Cameras
Underwater Digital Stills cameras have established themselves over the past few years as a vital tool when high resolution images are essential as an output from inspections or marine scientific observations.
The advantages over old wet film techniques are numerous and are outlined in the attached paper.
The digital cameras which we offer are normally supplied complete with a compatible flashgun which is TTL controlled by the camera and the more sophisticated system has a flashgun which zooms in sympathy with the camera, thereby increasing the possible range to subject.
For those digital cameras which are controlled remotely either RS232 or RS485 serial control can be factory set although it is a simple procedure to change this setting at a later date.
Transferring the images from the camera to a PC is accomplished using a fast USB link when back on the surface. Switching the camera between USB and serial operation is simply achieved by use of a remote control.
A board set is available which allows control of the camera and immediate transfer of images over a fibre optic link up to 10 Kilometres in length.A full software suite is included with each system in order to control the camera, transfer and file the images. The software package also includes an option to set up the camera for autonomous operation whereby it can be pre-programmed to secure images at predefined intervals over periods of hours, months or up to a year or more.
Digital Cameras
Use is made of the built in video capability of many of the modern digital cameras for framing and focusing the image before stills capture. The camera can be set in automatic mode thereby utilising in built intelligent electronics, ensuring that most images are correctly exposed and focused. When captured, a review of the image is displayed in video format for a period of two to ten seconds dependant on preset times, allowing for quality assurance prior to moving to the next inspection site.
The operator can remotely control the camera by using a GUI (Graphic User Interface) which can give access to all controls normally available in modern digital cameras along with the opportunity to set long line video drive compensation, choose to display video on the GUI window or switch off the flash if sufficient ambient light is available. The output from a humidity sensor in the camera can also be displayed.
In addition to control of zoom and image capture, manual control of focus, aperture and shutter speed can be easily selected. Full control of the camera through the menu icon can be gained allowing a myriad of options such as date and time setting, video standard changes and white balance select.
Intervalometer Function
Some of the more advanced cameras have a built in Intervalometer function which allows the camera to be deployed autonomously and pre-programmed to capture images at set intervals. This function has been successfully used by Ocean Research Institutes and produced quite phenomenal results far beyond their expectations. A 6000 metre depth rated camera was deployed and locally powered on a Lander which is sent to the Ocean floor for hours, days or even months in order to gather scientific data before being sent a command to return to the surface.
Cameras can also be simply triggered by a bottom contact or pressure switch allowing an image to be captured as the camera approaches the bottom or at a preset depth.
Fig 1 – GUI Camera Control OE14-208 Camera
Fig 2 – Replay Thumbnails
Surface Control
On surface controlled systems the images already stored in the flash memory (which can be upgraded to 4GB) can be replayed in the form of thumbnails or full image. The option to delete any images can be chosen at this time.
Control of the surface linked camera is normally by RS232 or RS485 serial link with the images being uploaded from the camera over a short USB link when it is returned to the surface. USB to fibre optic converter board sets are available which allows the camera to be controlled and images uploaded over up to ten kilometres of fibre optic cable.
Diver underwater digital camera housings have been available for some time now, although to date these have had limited depth ratings and have been aimed at the professional SCUBA photographer and sports divers and have provided considerable control of camera settings. A more rugged unit suitable for the commercial diver has now been developed. It is rated to 250 metres and its operation kept as simple as possible as it is recognised that not all divers are professional photographers and only direct control of zoom and shutter release is provided. In addition to automatic mode two selectable preset options can be programmed for selection of focus and exposure as appropriate. One of these options can be programmed to allow digital video clips to be taken.
Once the images have been uploaded to a PC they can be e-mailed to shore. Therefore, from an image being taken underwater it can now be on the PC of a decision maker thousands of miles away within a few minutes. Compare this with a photograph of yesteryear having to be developed and posted or hand carried to the desk of the same decision maker. In addition that decision maker now has the capability of zooming in to fine detail and spotting defects that the human eye may not see even if present at the work site.
Advantages of filing and retrieving digital images and the physical space savings are obvious. There could even be an argument made for reducing the amount of video footage required in certain circumstances.
An initiative run by Southampton Oceanography Centre called The Serpent Project has successfully brought together Oil Companies, Operators and Equipment Suppliers to take advantage of what would otherwise be standby ROV time on board drilling rigs. Marine Scientists can carry out or direct research in the oceans around the rig utilising these ROVs and as part of this research use digital cameras, which have produced some startling digital images.Examples are attached but be sure to visit http://www.soc.soton.ac.uk/GDD/serpent/ for further information and images.
Fig 3 – Prawn Hole Sponge
Fig 4 – My Little Sea Pony
ROV pilots enthusiastically involve themselves in the project and sometimes try to baffle the Marine Scientist.
Digital Underwater Cameras
