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Radar Reflectors on Motorboats |
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While DERA were carrying out their measurements, I watched the whole process on the large screen of a Decca Bridgemaster X band radar - typical of the radar you might find on a modem commercial vessel.
First, I watched as the Sonata turned through 3600 with no reflector. At a range of about 1.5 miles, I turned all the anti-clutter controls to zero, and set the gain control down to about a third of its maximum, so that the weakest signal was only just visible. With normal gain setting, the Sonata gave quite a good signal all the time, with the strongest response when it was beam-on and the weakest when it was .
within about 300 of head-on or stem-on. This pattern, incidentally, was repeated to a certain extent with each reflector under test.
In general the reflectors appeared to make very little difference to the echo as it appeared on the radar and, in some cases, the signal strength on certain headings appeared to be less with the reflector hoisted than without it. However, this wasn't always consistent, and on several occasions the signal strength on the second swing was quite appreciably different from that on the fIrst swing. The impression I formed was that the reflectors at times altered the strength of the signal, sometimes improving and on other occasions weakening the signal.
It was noticeable that some reflectors gave more consistent signals than others, whilst others produced large fluctuations, sometimes with only a relatively small change in aspect. As an observer I preferred the former, even though the returns were sometimes so weak that they demanded very close attention to the radar display and could easily be confused with sea clutter.
It would have been interesting to see how the individual reflectors improved the first detection range, since that's of vital importance to an observing vessel so a plot can be completed and avoiding action taken. It should be borne in mind that on large ships, most radar plotting is done with an Automatic Radar Plotting Aid (ARPA) and that it's not unusual for the ARPA to be left in automatic acquisition mode. This may mean that on a badly manned ship, the ARPA may be the only full-time lookout. Certainly one hears stories of watchkeepers relying on radar to keep the lookout even when they would be better advised to use their eyes and a decent pair of binoculars and I've been told of one officer who was happy to read a book on watch and only glance at the radar every 15 minutes - while doing 20 knots!
It's also worth mentioning that had the tests been carried out in dense fog, the results would almost certainly have been much worse due to attenuation of the radar pulse by the water droplets which form the fog itself. S-band radar would be less attenuated by fog but would be less effective at detecting a small contact |
Equipment 