Articles on SharpEye™

How the Technology Fits In

NT radar fits in well with the evolution in marine navigation currently being defined by IMO and IALA, known as eNavigation. The growing integration of radar data with information from other sensors and also from databases, such as digital charts, needs increasing levels of integrity in the radar.

eNavigation

NT radar can supply this. It has an inherent ability to improve the detection of targets in clutter by using the frequency data (Doppler) in the returned signal.

The potential capabilities of NT radar can be increasingly exploited as techniques evolve, giving an almost unlimited performance upgrade path into the future.

Its implementation relies on the affordable availability of sophisticated microwave technology and formidable processing power. Perhaps unexpectedly, these should lead to greater reliability in the equipment, enhancing safety and reducing cost of ownership. This happens for a number of reasons. The very high levels of integration needed reduce the number of individual components; much analogue circuitry, prone to noise and drifting effects, is replaced by reliable digital technology; and no high voltages need be used, significantly reducing the chances of component breakdown and interference effects.

The Doppler processing capability of NT radar and the extra reliability are not the only advantages. For instance, the move from fixed frequency magnetrons to flexible solid-state transmitters allows additional benefits to be gained by the use of frequency diversity techniques.

Frequency diversity means that the radar utilises a transmit signal on two or more different frequencies. This gives an improved detection capability as there is a much greater statistical probability that the target will be visible, particularly in clutter. It is relatively straightforward to make a solid-state radar transmit consecutive pulses at different frequencies or even transmit two (or more) signals at different frequencies, simultaneously. The frequencies have to be quite far apart for best results but there is ample range within a single radar band.

High performance magnetron-based radars, mainly used in military systems, have obtained the benefits of frequency diversity by using two separate transmitters. However, this is an expensive option for the commercial marine market, compared to that potentially available from the use of NT radar.

Other military inspired techniques can also perhaps be used for NT radar, making use of the affordable processing power becoming available.

For instance, an interesting concept is known as 'track-before-detect'. Despite its name, the tracking and detection processes are carried out simultaneously. Current marine radars first detect the presence of a target (a blip on the radar display) and then, in effect, use standard algorithms to track the movement of the blip across the display.

For track-before-detect systems the simultaneous tracking capability helps the basic detection process. Knowing where a target is likely to be, assists detection. This technique has the potential ability to detect and track moving targets in very high levels of clutter that would be otherwise impossible using conventional techniques.

Operating NT radar

So what about using NT radar - will there be any differences from conventional systems? In principle, quite different controls could be made available but for the foreseeable future IMO requirements will still insist that the familiar gain, rain and sea clutter controls are provided.

Also, similar processing options selectable on existing radars, such as scan-to-scan correlation, are likely to be also available. Signal waveforms, such as pulse length and pulse repetition frequency, will change appropriately as the operator switches the displayed range, similarly to most existing radars. There may be less need to have any operator overrides on these settings. It is possible that some NT radars may always transmit a signal waveform that ensures optimum performance at all ranges, whatever the current maximum range selected for display by the operator.

This, in particular, allows a number of integrated navigation multifunction displays to show the optimum radar picture, whatever the user-set range on each display.

The controls selecting radar display options, for example maximum range, have no reason to differ from existing modern radars. Also, the control of tracking functions should remain similar. In general, it is unlikely that there will be a proliferation of additional controls.

Potentially interfering signals from nearby conventional radars will not affect a well-designed NT radar. However, an NT radar operating on the same frequency as a conventional radar is likely to cause non-suppressible interference to the conventional radar because the standard methods of interference rejection are generally unsuitable for NT radar signals.

For this reason, NT radars with incompatible transmissions should never transmit on the same frequency as a within-range conventional radar. Therefore, designers of such NT radars need to provide means to ensure that interfering transmissions are not made.

Rejecting radar interference between NT radars will also have to be carefully thought out by the radar designer. The radar operator may be provided with a control that is able to eliminate any observed interference.

Although such a control should be simple to operate it may in fact perform a variety of complex actions, such as changing transmission frequency, pulse repetition frequency and pulse compression waveforms. This detail would not need to be apparent to the user.

It may be possible to provide automatic processes that properly look after all interference aspects, without operator intervention.

Meeting operator needs

The concept of NT radar has been introduced to improve detection performance. Existing radars do not meet the detection requirements of mariners under all encountered conditions.

On conventional radars critical targets can readily disappear into clutter or, more dangerously, not appear at all. In adverse conditions the poor radar visibility of targets such as leisure craft, small fishing vessels and non racon bearing navigation marks is of constant concern to the navigating officer.

The Master of a large container ship emailed just recently, "Our problem is (and always will be) detection of small wooden vessels in restricted visibility, especially in Asia".

NT radar technology has the potential ability to give this Master what he needs but does not think is possible.

Ironically, the advent of AIS for small vessels (AIS Class B) increases the need to have better ship radars. Some incautious users of Class B systems will inevitably consider that their AIS will make them always highly visible to ships. For this reason they may use less caution than is currently the practice when in the presence of ships in adverse conditions.

If such users do not notice a failure of their own Class B, it will be solely up to the ship's radar - in conditions of poor visibility - to detect such craft. A well-designed NT radar should be up to this.

Although NT radars will give the operator the ability to optimise manually the displayed image, automatic processes may well be superior to the capability of most users because of the potential sophistication and power of its processing system.

Experienced navigators of today take pride in their ability to optimise the radar. However, many young navigators, brought up on the preciseness of computer technology, are expecting that optimum performance should always be maintained automatically.

In principle, if this is possible it is no bad thing, as it increases the time that the navigator has for improving total situational awareness, rather than concentrating on adjusting the radar. NT radar therefore has the potential capability to increase situational awareness in addition to that obtained by its improved detection capability.

The next few years will be an exiting time as manufacturers get to grip with the new possibilities. Such radars, suitably integrated with AIS display features, are capable of meeting the real requirements of users and should contribute significantly to safety.

Shipping companies may also be influenced by the potential reductions in cost of ownership.

About Andy Norris

Andy Norris works as a consultant in the international marine navigation sector. He is also Chairman of Technical Committee 80 of the International Electro-technical Commission (IEC), responsible for producing international standards for marine navigation and radio communication equipment in close cooperation with the International Maritime Organization. He holds the visiting position of Special Professor of Navigation Technology at the University of Nottingham, UK.