WAYPOINT - Eyes and ears
Dr Andy Norris, an active Fellow of The Nautical Institute and the Royal Institute of Navigation, explores why our eyes and ears are still the best lookout tools we have
Sight and hearing dominate the stated requirements for lookout in Rule 5 of the Colregs. Of course, the Rule also goes on to state “as well as by all available means appropriate in the prevailing circumstances…”. Although some may believe that the dominance of sight and hearing only reflects the ‘pre-electronic’ history of maritime navigation, it is consistent with the latest concepts of best navigational practice – even when that navigation is fully autonomous.
This is because the optical and acoustic scenes (what you – or the sensors – can ‘see’ or ‘hear’) give fully up-to-date information, totally independent from that given by other important navigational aids, including charted data, radar, GNSS, AIS, speed logs, etc. In addition, most aids to navigation (AtoNs) are designed to be readily visible, and are often artificially lit at night. Some aids also generate specific sound signals.
For the human navigator, it is especially important that data collected by sight and hearing is constantly analysed by the human brain. In some circumstances, the information you get from sight and hearing is enhanced by information from what you feel – vibration, movement and acceleration.
WE MUST CONTINUE TO USE OUR EYES AND EARS TO ENABLE SAFE NAVIGATION
Seeing the light
The optical scene is so important because virtually all objects naturally reflect light. Because the wavelength of light is very short (several tens of thousands of wavelengths in just one millimetre) it enables extremely good discrimination even when using very small sensors, such as human eyes, to detect an object, and identify what it is and whether and how it is moving. In comparison, the wavelength of an S-band radar is about 10cm – around 200,000 times longer than that of light.
It is therefore much less effective in discriminating objects. Of course, the optical scene becomes severely degraded in common conditions such as darkness, mist or fog, hence our interest in nonoptical sensors.
In poor optical conditions, sound is the only ‘natural’ way of detecting targets at sea. Nowadays, such signals are typically picked up by external microphones and relayed to the bridge staff via loudspeakers. In fact, it is quite easy to design systems that automatically calculate the bearing of sound sources, but at present they are not commonly used on commercial vessels. However, future use on autonomous systems will change this situation, even on manned vessels.
Night vision
The optical scene remains highly valuable at night. In reasonable conditions it is easy to detect, by eye or electronically, light emanating from vessels and other objects, which is why we have a continued interest in navigational lights. Of course, objects that do not emanate artificial light cannot be optically detected in complete darkness, except by using searchlighttype techniques. Unfortunately, if used irresponsibly, searchlights can dangerously affect the visual detection capabilities of other vessels, effectively becoming an optical jammer.
As well as being jammable, optical information can also be spoofed. A common example is the use of camouflage on military vessels. Shortrange sound jamming and spoofing are also possible. Importantly, both optical and sound spoofing/jamming are extremely difficult to implement over an extended area, in contrast to radar, GNSS, AIS and radio, further emphasising the value of optics and acoustics.
Modern technology could considerably enhance the detection of both the optical and the acoustic scenes on both manned and autonomous systems. In the fulness of time, Rule 5 may need to evolve to emphasise ‘optics and acoustics’ rather than ‘sight and hearing’ – but, today, we must continue to use our eyes and ears to enable safe navigation.
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