26th February 2008, 10:58
Here is the pic of the radar plot taken on Hector Heron back in May 1973, I don't recall the make or type nr. It's on the 12nm range, heading north east towards the Straits of Hormuz.
The southern coast of Iran is to the north west, the odd shape around the centre is, I was told at the time, the echo return from a temperature inversion layer, giving a quite misleading view of our surroundings at the time. I don't recall the time of day or night, but I do remember there was nothing visible from the bridge, except flares etc more than 24 miles away.
(See also Msg 36 in the Longest QSO thread.)
26th February 2008, 16:15
Somewhere in the Eastern Mediterranean the 2nd mate called me to the bridge one afternoon to look at the radar. There on the screen, 48-mile range, was the radar echo of the coast of Crete which, at the time, was over 300 miles away. Amazing what a little temperature inversion will do.
26th February 2008, 20:13
interesting pic andy
26th February 2008, 20:26
I remember vaguely, from my radar op, course in the RN, we were informed of this phenomina, I recall the term for it was Anonymous Propogation, or AnoProp, signal ricochets from weather or temp layer and if returning signal reaches point of origin, will give true radar image of coast many hundreds of miles away. All of which tells you absolutely nothing, other than I am not yet senile![=P]
26th February 2008, 22:15
Radar transmits a pulse of RF energy, then displays the returning echo's on the screen -this happens typically 1000 times a second.
Normally Radar waves travel in straight lines hence depending on the height of the scanner and target a range of 40-50 miles is about the limit - when these strange weather induced propogation conditions occur ( ducting, super refraction etc) radar waves (keeping it simple) bend around the curvature of the earth (these waves would normally go straight into space). If they find a strong target and bounce back, they can arrive at a time when the radar is receiving echos from the next transmitted pulse (or even pulses after that! ). these reflections will be displayed showing a distorted ghost picture of a coastline which can be hundreds of miles away.
The picture above is an excellent example of typically what may be seen.
26th February 2008, 23:51
Gareth, that was called STAR Second Time ARound. In radar systems we had special circuits to eliminate this. When the Rejection system was dissabled, you'd see some weird effects, especially with short range stuff.
When I was explaining radar to my juniors, I used to amaze them with my explanation of 'the Wonders of Radar'.
We alll knew that electrons are green (from the green display on oscilloscopes). OK. Well, those green electrons go through pink wires, around grey racks into a grey Klystron (a big high power valve for the uninitiated). They are then sent through crimson waveguides and hit an olive drab ( a military shade of green) reflector where they go out into the wild blue yonder. they then hit an aircraft.Now this aircraft can be ANY colour! They are then bounced back through the wild blue yonder, hit the olive drab reflector, then travel down the crimson waveguide, through grey cabinets and pink wires and show up on the display as ORANGE! and that is the 'Wonder of Radar'!
27th February 2008, 00:56
This explains why rainbows dont show up on radars - too many colours !(Jester)
27th February 2008, 12:05
No pot of gold, either Gareth :(
27th February 2008, 15:17
interesting pic andy
Thanks Sparkie, it was on the 3cm radar by the way.
Here's another one.
This one was taken outward bound from Seven Islands bound for Rotterdam in Feb 1975, somewhere down the St Lawrence estuary, heading south east to go south of Newfoundland. Again it was on the 3cm radar - can't remember the range or make- may have been a Raytheon.
It shows quite well the clutter from the surrounding ice, which wasn't than thick - thank god as we were not ice strengthened !
29th February 2008, 14:00
Great Picture, Truth is Stranger than Fiction, quite clever of you to take the picture of this phenomenen, Good thinking,
I was on a Tanker passing Ceylon Westbound about 1965 and had a strange picture on the Radar, Marconi Radio locator 3 (I think All tube's). Could not make out the Targets ahead of us, as there should'nt have been any., Eventually it dawned on us. ''The Gulf of Aden and South Red Sea, with Somalia and Yemen booming in 5/5 on the Radar., We called the Skipper., and he just Grunted, ''Its always like that around here'' Anything unusual was kept to ourselves after that.
29th February 2008, 22:00
Thanks Athinai, it was just something I thought might become of interest someday. I recall the lecturers at Norwood Tech trying to describe things like this, and thought I'd help them out with some pics - they never got them though ! I've a few more somewhere, up in the loft with all the other slides ...
Very easy to take, just hold the shutter open for a couple of sweeps, and hope the engine vibrations aren't too bad.
29th March 2008, 23:29
Heading east through the Med on board the Bencruachan, the Ben Boat that broke her bow off S.Africa, I called the old man urgently to the bridge because of radar immage about 48 miles distant. A very solid echo, we were sh*****g ourselves thinking it was another freak wave then realised it was the coast of Egypt several hundred miles away, bloomin' atmospherics!