N/B question about marine radar

[nickjaxe]

Hi all a mate of mine is a keen aviation buff likes to listen to atc on his airband radio and track flights ect, we were talking about radar and he asked me being a boat owner, if a marine radar ie the small budget type you can buy these days was mounted on say the top of a house would it show aircraft or are marine radars not able to do that, I have no idea as I have never used one.

Regards Nick.

 

[Talbot]

The biggest problem is the elevation capability of the aerial. a small ship radar is perfectly capable of detecting and displaying a large helicopter out to abt 6nm, and thus would display an aircraft at at least 10nm, but unless you live close to an airport, they will be too high to be detected.

 

[snowleopard]

i was reading the YM article on budget radars this morning. a typical 2kw scanner produces a beam 6 deg wide horizontally and 25deg vertically, in other words it will 'paint' anything up to 12.5 deg above the horizon.

the power is capable of picking up objects up to 24 miles but aircraft aren't designed as ideal reflectors - they mainly rely on active transponders rather than passive reflection.

 

[ClassicPlastic]

Aviation radars are either Primary or Secondary. The Primary radar relies upon receiving reflected radar energy, and uses a very big antenna and quite a lot of power, together with devices such as a Moving Target Indicator (MTI) which suppresses any returns not moving faster than a certain perceived groundspeed. Secondary radar (SSR) uses a transmitted pulse which interrogates a Transponder on board the aircraft, which in turn sends a coded reply. The SSR antenna is much smaller, but still about the size of the revolving radar on a big ship.

Strictly, to say that aircraft don't rely upon Primary radar is incorrect - it gives the highest accuracy, and is why only Primary radar is used for radar guided approach to 1/2 mile approach, where SSR is restricted to 2 miles.

Marine radar will not show aircraft unless they are (a) very close by, in aviation terms, (b) very slow moving, and (c) very low.

Your chum is unlikely to get any joy at all out of his idea. There were some web-based 'flight tracking' programmes available, which showed radar pictures of various parts of the world. We used one in my previous airline's Ops department, to keep an eye on flights. However, since the terrorist attacks on the WTC, these things are no longer considered such a good idea, and I would think that your chum is unlikely to find a publically available website. Subscriptions charged to airlines and the like are costly.

He might find some joy at www.pprune.org, where a question in the right forum might elicit help.

 

[ClassicPlastic]

Sorry, I should clarify that my post above relates to ground-based ATC or Air Defense radars, the radar equipment on board aircraft are Primary and are optimised for seeing weather, the ground ones are optimised to filter weather out.

Also, it's worth adding, for interest, that many modern ATC Centres use a computer-processed radar 'picture' derived from many ground-based radar heads, both Primary and Secondary.

Finally, your chum needs to be very carefully about use of his scanner, as it is very easy to contravene various Acts, for example, by communicating information received, even if this is only talking about what he heard on his scanner, when he's in the pub. I think the Ofcom website may help with this. Personally, I would add that the fact that enthusiasts listen to airband channels, does cause some problems for pilots and ATCOs, and makes us very circumspect about what we say, especially in an urgency or emergency situation.

 

[toad]

When I bought a radar at the London boat show some years ago ,I was playing with it in the shed with the scanner in the garden angled up by about 30deg.Aircraft on the Stansted flight path(I think)were very clear at about 8 miles .So yes it will work but only over a small arc,also the small screen and speed of the target ment that it was only there for a few seconds.

 

[Talbot]

Your post is correct as far as the standard airport radar antenna are concerned. However you need to understand the reason for this The primary radar used for air traffic control is a much lower frequency than a boat radar, thus will work up to a much longer range. The size is also required to enable the aerial beamwidth to be as narrow as possible to enable better air control. Both this low frequency and wide aerial demand a much higher power output. The greater ranges are achieved by by reducing pulse repetition frequency (PRF). Your boat radar is designed to achieve a much higher data rate at short ranges, so has a much higher frequency and a much higher PRF. However, the lower power and design of the processor on small boat radars may mean that the fast aircraft are ignored as being electrical noise. Helicopters and slower non-commercial aircraft will show on the display provided that they are within the aerila coverage and within the chosen range of the display -- I should know I have spent more years tracking aircraft on different radar than I care to remember.

 

[ClassicPlastic]

Thanks you Talbot, for dotting some i's and crossing some t's there... I had deliberately kept it non-technical for the forum. Perhaps we both sat in similar classes at Hurn?

 

[Talbot]

No - just 30 years experience (and appropriate training) in grey war canoes /forums/images/graemlins/cool.gif

 

[nickjaxe]

Thank you guys for your very informative replies very interesting.

Regards Nick.