One of the important elements in ROV mission performance is the quality of the visual information that the ROV passes back to the operator. Sending an ROV into the water lets a human being put eyes on the target, and those eyes need every well-lit pixel they can get.
What lets an ROV operator get the highest-quality underwater visual information back from his or her vehicle?
A significant component of video quality is the video format being used by the camera. For most of the 20th century, video cameras used either the NTSC or PAL standard. NTSC displays had (and still have) 480 lines of usable vertical resolution, while PAL used 576 lines. Both the NTSC and PAL formats had 4:3 pixel ratios, meaning that an NTSC picture is 640x480 (not coincidentally, the same screen size as the old VGA computer monitor standard) while a PAL picture is 758x576. These resolutions were adequate for the black and white and color TVs found in most homes up until around 2010.
Both PAL and NTSC are interlaced formats, meaning that every other scan line is refreshed at each frame (i.e., half the picture is refreshed in one frame, the other half on the next frame). This produces a smoother picture at reasonable frame rates, with the unfortunate downside of producing jitteriness during motion shots. Neither NTSC nor PAL would make good formats for underwater video for this reason, even if their low resolution was not an obstacle: an NTSC frame has only 307,200 pixels and a PAL frame has only 436,608.
Modern video cameras use one of the HD (high-definition) standards. The lowest form of HD is 720p, which provides 720 lines of vertical resolution with a progressive (non-interlaced) scan. This provides 921,600 pixels, which is a step up from NTSC or PAL but still leaves something to be desired.
The midrange HD standard is 1080i, which has 1080 lines of vertical resolution but unfortunately reverts to an interlaced display. This provides 2.07 megapixels per frame, but only 1.03 megapixels refresh with each frame, leaving the video subject to jerks and jittering. The highest HD standard is 1080p, which provides a full 1920x1080 2.07 megapixel frame without interlacing. 1080p is the best commercially-available picture format; 1080p video at 24 frames per second is the equivalent of watching a Blu-Ray DVD on an HDTV. 1080p at 24 frames per second is the gold standard for underwater video quality.
However, size is not everything, and there are other important elements to consider when maximizing underwater video quality.
One critical area is lighting. In many ROV applications, such as water tank inspection, there is no natural light at all, and even in open water the sunlight diminishes drastically with depth. At 10 meters down in crystal clear water, there is only about 25% as much light as at the surface and at 100 meters down there is only 0.5% as much light. Rough water and particulates in the water can make things even dimmer. Even if you have adequate natural light for your purposes, remember that water causes a distortion in the color spectrum; red light is absorbed most rapidly causing things underwater to tend strongly towards appearing blue or green. If your application needs accurate color, or if you need more light than is naturally available at your depth, then artificial lighting from the ROV itself will be necessary to get good video quality underwater.
The optical characteristics of the lens and the mechanical elements of the camera itself are also important in underwater video work. A wide-angle lens allows a very close focus on objects in the field of view, which means that the operator can get very close to the subject and still have a clear picture. A camera that can tilt and pan while the ROV hovers in one place can get even tricky shots into close focus. Of course, the maneuverability and ease of control of the ROV itself can be determining factors here – you have to be able to get the camera to the target, so an ROV that is easy to control is one from which it will be easy to get good video.
The combination of a high-quality video format, a high-yield lighting array, a well-designed optical system, and a maneuverable, flexible ROV will provide the best possible underwater video quality for any application.