Underwater video cameras fitted to Remotely Operated Vehicles (ROV) and Autonomous Underwater Vehicles (AUV) for navigation purposes must be chosen carefully in order to give the ROV pilot/operator maximum field of view and through water visual range with best possible sensitivity, contrast and resolution in low light and turbid water.
Black and white (monochrome) Silicon Intensified Target (SIT) or CCD underwater cameras rather than colour tend to be the most popular for this application because of their superior performance in low light and murky water situations.
Important Factors
The following are some of the most important factors to be considered when choosing a suitable navigation camera:
The better the sensitivity the better close range low light performance is possible.
Lower artificial light or the use of ambient light improves the viewing range in turbid conditions.
The viewing range of current CCD based cameras will tend to be less than the SIT because of the inherent limitations of the CCD’s spectral response characteristic.
The solid state CCD is more rugged and therefore less prone to physical damage than the SIT tube although great care has been taken to minimise this risk through careful design.
The CCD is virtually immune to damage through over exposure to intense light sources and care has to be taken to ensure that the SIT is not subjected to such over exposure.
Considerations
When choosing an underwater camera specifically for navigation purposes it is important to consider camera performance criteria along with the physical constraints of seawater:
Light Sensitivity For underwater navigation applications this is one of the most important parameters. Cameras with superb light sensitivity offer a number of advantages:
Long range viewing
Ambient light operation even in excess of 200 metres depth with a SIT camera.
Best operation in turbid water conditions
To reduce the chance of ambiguity Kongsberg Maritime quote underwater camera sensitivity in seawater conditions and is always quoted in Lux or part of. e.g. 1x10-4 = 0.0001 Lux.
Spectral Response One of the fundamental physical properties of seawater is that it does not transmit all colours of the light spectrum equally. This property should be considered when choosing a camera for underwater navigation purposes as the optimum response of a camera within the spectrum can vary considerably.
The spectral response of the SIT is ideally suited for use underwater. It provides maximum response at around the same wavelength as that of the best transmission in seawater, around 450 nanometres, the blue/green region.
The spectral response of the typical CCD sensor peaks in the red and near infrared regions of the light spectrum.
This effect explains why the SIT camera in practice performs better at long ranges than most CCD cameras, even though the measured light sensitivity (in air) of the CCD sensor is greater.
Resolution Resolution is a measure of the level of fine detail that the camera is capable of resolving.
Lens Wide-angle lenses are a popular choice for underwater navigation cameras because they provide coverage of large areas at relatively close range. Wide-angle lenses also have a good depth of field removing the need for the operator to adjust focus. Aspheric lenses are the most efficient at transferring light through to the sensor.
Cameras fitted to ROV and AUV 
