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Post by olaf3sky on Jun 3, 2010 12:27:22 GMT
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Post by markt on Jun 3, 2010 18:21:43 GMT
Thanks for the update Olaf!  |
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Post by mesospheric on Jun 3, 2010 21:24:24 GMT
Thanks Olaf. I wonder if I might ask you about pmse in the early years of radar? There are interesting reports from world war two of strong and unidentified large scale echoes on VHF radar sets. I don't think anyone at the time managed to figure out what these were, after initial concerns that they were huge aerial invasions from Germany.
Do you think these were In fact early pmse detections?
Kind regards from Wales.
John
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Post by olaf3sky on Jun 3, 2010 21:42:17 GMT
... I wonder if I might ask you about pmse in the early years of radar?... Do you think these were In fact early pmse detections? I am very sorry John... Interesting question but I have no answer... I watch these PMSE radar data since a couple of years as amateur + I have heard about the WWII radar story - but that is all I can say to the WWII idea... Maybe another one knows more (details) about these WWII radar echoes? |
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Post by ediacara on Jun 4, 2010 3:50:06 GMT
It is a very interesting question!
What I know that WW2 radars used for detecting objects could hardly "see" any kind of small particle phenomena, only some very weak signals could have been received from atmosphere, mostly from the ionosphere.
The Germans used 1-23 cm wavelength radio signal for their radars in the WW2.
The other question is the range of the radars used at that time: most of them were set for detecting backscatter of relatively near objects, although the British defense had one radar system with a range of about 300 kms, I think the main question is regarding these kinds of long range radars. The British defense radar system (Chain Home) used 10 - 15 m wavelength, a bit later they used 1,5 m, even later on only 10 cm. I can hardly imagine that this wavelength can get significant backscatter from micron sized particles of a possible NLC.
10 cm average wavelength is what used in our days for weather (precipitation) doppler radars, the wavelengths are refined for the aimed kind of weather phenomena (rain, snow, hail etc.). While these are still present in quite big particles, NLCs are made of small ones, but as we, humans can see them as clouds from a great distance, some radars might have seen it in the same way, some blurred distant backscatter "haze" might have appeared on the radar operators' screens. I don't know how refined the signals were for planes or groups of planes in WW2 but I have read about the radar operators' job was hard, they had to be well trained and experienced, and had to concentrate on the kinds of signals. There might have been people among them to misidentify a weak signal "haze" as a distant group of planes, I think.
Even today the military radars are able to catch the signals from birds (e.g. starlings, geese ), so now all radars are helped with a filtering process to wash these "false" backscatters out from the results of their measurements. This was set simply because of the practice and experience of telling the difference of some special objects' backscatter. In the WW2 the filter (=experience) was needed to be part of the operators, not the physical system.
It would be easier to get an answer if today's radar images were unfiltered and investigated while NLCs are on. It would be an easy experiment, if someone has a possibility to get unfiltered radar data. This winter we in Hungary had a big fireball, and as it was suspected to fall down somewhere near us, we tried to look after if air traffic control or military radars could see its backscatter while falling downwards. We have talked to some people working in these fields, but they all said that they don't have unfiltered radar images, they only save the filtered ones in their database. So filtering is now a main feature built into the radar systems, I think.
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Post by mesospheric on Jun 4, 2010 5:42:54 GMT
Thank you very much for the very interesting and thought-provoking replies. I will, however, leave the suggested experiment for someone else to do - I have too much work already with the BBC at the moment! I'm sure it would even make an interesting TV programme in itself - recreating a WW2 radar.
The issue of range is interesting. I suppose the range you mention is in fact a near-horizontal range, as the important thing was to detect aircraft approaching as early as possible. So I further guess that it's a question of how high the lobes of the radio detection extended, and for British radars at least, whether looking towards mainland Europe (south and east ) made the detection of PMSE unlikely? I wonder if German radar, looking north and west, had a greater chance of seeing atmospheric reflections?
Always more questions than answers!
Kind regards,
John.
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Post by ediacara on Jun 4, 2010 16:19:35 GMT
John, yes, the range is "horizontal" (never really horizontal but an angle to include the flight altitude). The modern civil air traffic radars' range is about 800-1000 km, but they don't look above 13kms altitude (they don't deal with the data coming from that altitude). Military radars (or some of them) must have a bigger angle, as it would be logical, they must also detect rockets coming from a more high region.
I'm not too much into history, but technical developement was always an interesting question for me. I don't know if the British radars were also set to detect German V rockets or only planes?
If someone is into this theme it might be a good PHD work to investigate it in connection of NLC or other celestial phenomena. :-)
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Post by johnm on Jun 8, 2010 20:06:44 GMT
I believe the 2nd WW radars were quite capable of picking up Meteor Echoes. I think this was the reason that Sir Bernard Lovell of Jodrell Bank started using 2nd World war radars to track meteors and then went onto Radio Astronomy. From Memory the radars may have been UHF or shorter wavelengths from the size of the dish. Does anyone on this board have contact with Sir Bernard and could they ask him about WW2 radar and NLC ?
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