WAYPOINT - Reassessing radar: then, now and in the future
Dr Andy Norris, an active Fellow of The Nautical Institute and the Royal Institute of Navigation, looks back at the history of radar and wonders how much it has really changed over the years.
Back in 1946, the first requirements for civil marine radar were laid out to manufacturers during an international meeting on radio aids to marine navigation. Since then, it is remarkable how many of the basic performance requirements for radar have really not changed, as the table to the right shows.
The 1946 performance requirements matched not only what was technically feasible at the time, but also what would provide highly useful information for the marine navigator. The latest requirements, updated by the International Maritime Organization in 2004, only really differ with regards to how information has to be shown to the user, taking advantage of the advances in modern digital processing and display technologies. In general, the basic requirements for target detection performance have hardly changed at all, although some useful enhancements have been made to the accuracy of the system.
Today’s user courses for marine radar spend a lot of time on the performance limitations of radar, and rightly so. One key point is that targets can become invisible when conditions at sea deteriorate, due to the effects of sea and precipitation clutter. The statutory range requirements for marine radar are labelled as ‘in-the-clear detection ranges’. IMO does not specify the allowable degradation in adverse conditions. However, it does insist that the performance degradation for certain defined rain and sea-state conditions is mentioned in the equipment’s user manual.
Taking degradation for granted in this way seems to be totally at odds with what navigators need. After all, when visual conditions deteriorate, the instinct is to rely more and more on the radar. While technology has always aimed to lessen these effects as much as possible, the potential for significant further improvement has been somewhat ignored in recent years.
Military precision?
Basic concepts for further improvements were developed many years ago by the military, in order to be able to see such things as submarine periscopes. It was realised that, if the received signal could be precisely compared to the actually transmitted signal in both amplitude and phase, then the effects of clutter could be reduced by a factor of hundreds or even thousands. Today’s implementations of so-called coherent radars, using modern semiconductor devices, can make a very sophisticated system much more affordable, even for the commercial market.
Unfortunately, the current IMO requirements for radar do not promote significant moves in this direction. In some ways, we still have a 1940’s mindset of what radar can and cannot do for us. As with all onboard equipment, users of radar should be encouraged to express their own thoughts if they see a need to improve performance.
Physics and affordability obviously get in the way of creating the perfect product. However, when advances are possible, we should do all we can to meet users’ needs. Although such radars are more expensive to buy than standard systems, they are more likely to reduce accidents and improve navigational efficiency, therefore representing valuable cost savings, financial and otherwise.
| Requirement | 1946 standards | Latest IMO requirements (2004) |
| Basic in-the-clear detection ranges: | ||
| Shoreline rising to 200 ft /60 metres | 20 miles | 20 NM |
| Second class buoy/channel marker | 2 miles | 2 NM (X-band), 1 NM (S-band) |
| 30 ft/10 metre vessel | 3 miles | 3.4 NM (X-band), 3.0 NM (S-band) |
| Bearing accuracy | 1° | 1° |
| Bearing discrimination | 3° | 2.5° |
| North-up stabilisation capability | Yes | Yes |
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