There is no universal underwater vehicle system–nor is there an optimal underwater viewing system. Depending on the application, one viewing or inspection technique will out perform the other. Low light TV provides long distance viewing whereas color provides contrast, but requires high illumination, which results in high back scatter, however, the camera produces good close in resolution. Accordingly, larger systems will have a combination of several types of underwater viewing and documentation subsystems, and smaller vehicles will carry what they can, but what they do carry must be matched to the task at hand.

Camera location and movement is critical. The main TV cameras should have the capability to move—rotate (pan) and pitch (tilt) to aim the lens in the desired direction. The operator’s cameras should have a full field of view in the direction of travel to avoid hitting obstacles, in addition to a full view of the working area (including the manipulators' area of reach). Additionally, the TV cameras should have overlapping fields of view where possible to allow cameras to operate as backups systems. The ability to view behind the ROV to watch the umbilical or tether cable for fouling or snags, and to inspect the ROV itself (to check for damage or problems) is desirable. Aiming the camera requires that you know where the camera is pointing. The best method of showing the pan and tilt information is to overlay it on the TV screen with the actual picture so that the viewer does not have to look away from the picture.

An important part of navigating an ROV is seeing where the vehicle is going. TV cameras have problems similar to human vision—a lack of sensitivity at low light levels. Unless a stereo camera system is used, depth perception is non-existent. Therefore, a dual perspective camera system is almost mandatory for any complex work tasks

Modern ROV systems have the capability of carrying 10 TV cameras and operating 5 or more simultaneously. With the advent of components such as Focal Technologies' fiber optic video and data multiplexer, up to 8 uncompressed video channels and 15 bi-directional data channels may be transmitted on one single-mode optical fiber. ROV umbilicals may carry up to 12 fibers, of which several are designated as spares in case of breakage.

Closed circuit television/video systems, unlike film type photographic equipment, provide real time feedback and documentation to the operator—an absolute necessity for direct operator control of the system. Although the images acquired do not have the very high resolution available with hard copy photographic images, the operator has the warm feeling that he does have good documentation of the object being investigated without the concern of returning to the site because of a problem with the photographic camera. And, new frame grab technology can give the operator a hard copy of the video image, albeit at a lower resolution than other techniques.

Cameras in use include Silicon Intensified Target (SIT), Silicon Diode Array (SDA), and Charge Coupled Device (CCD). Low-light-level (LLL) cameras, which operate with illumination levels hundreds and even thousands of times less than conventional tube or CCD cameras, have been used in the underwater environment for more than 25 years, with the SIT the most commonly used. New image intensifiers with upgraded features are now available for use with ICCD (intensified CCD) assemblies and are likely to become the sensors of choice in the future. These intensifiers can significantly improve low-light performance, and provide a larger variety of spectral response.

There are several benefits of LLL cameras. Lighting is a major item in the power budget for many television systems, thus LLL cameras can significantly reduce this budget. This is an especially important consideration in battery powered vehicle design, and also for interconnecting cables, where their size and weight can be reduced. LLL cameras include significant reductions in size, weight, and power consumption and improvements in reliability, stability and repeatability.

It was only a matter of time before the LLL cameras became integrated with the computer. Insite Systems, in their Gemini camera (see photo), has combined advances in computer and surface mount technology through the use of an onboard microprocessor that enables the user to control virtually all of the camera’s internal settings to optimize performance under any lighting condition. The operator can quickly adjust the video level, high frequency compensation, AGC, iris setting, or return the unit to factory settings. Trouble shooting is performed by built in diagnostics that monitor the camera, which can be linked via modem directly to the factory for on-line diagnostic assistance. Obviously, such technology will really springboard underwater cameras into the computer age.

DeepSea Power and Light (DSPL), in addition to their line of underwater lights, offers underwater imaging solutions with its excellent line of cameras. The miniature Multi-SeaCam (see photo), is designed as an inexpensive, small, fixed focus, monochrome and color camera with depth ratings to 6,000 m. ROV operators find the miniature camera particularly useful as a manipulator or tether-monitoring camera. An additional benefit as a manipulator camera is the sapphire port, which is nearly impervious to scratching (except with a diamond), and holds up extremely well in the high-impact working environment of a manipulator.

Regardless of the type of camera chosen, today’s advanced designs are allowing compact and efficient systems that provide an excellent end product.