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BiggarDigger

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About BiggarDigger

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    Male
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    Astronomy (obviously!), IT (work - ugh), electronics and radio engineering, meteorology, fresh air and wide open spaces.
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    Biggar, Scotland
  1. That is a very good question, which I cannot answer with certainty, but I think there is a real world effect. It's possible that some of the effects seen could be artefacts of the FFT. Also, some of the bifurcation may be frequency scattering. However from the traces I've seen there are a number that I cannot explain. Here's a better one: I've seen traces wher bifurcated returns appear from nowhere after the start of an echo, or extend on after the "primary" carrier frequency echo drops into the noise. GRAVES trasnmits a carrier wave, so the scatter returns should closely approximate to a carrier wave, such as this one: The vertical "ticks" on the second traces correlate to and are assumed to be artefacts of the 2-second azimuth switching of the GRAVES radar. The wideband noise occurs at the switching points and may be further artefacts of the FFT, or saturation of the SDR. I don't recall seeing many of these artefacts on bifurcated returns. I do have even better examples of bifurcation which clearly shows two or even three traces in the time domain. If I can find them, I'll post. My guess on your superb echoes, is that that they represent the modulation of the TV signal, possibly coupled with some bifurcation too. Richard
  2. If receiving a TV transmitter, you'll also have modulation on the signal too. Even though the TV signals are amplitude modulated, I suspect when viewed on the waterfall plot you'll be something similar to the charts presented in both time and frequency domains. However, 55Mhz scatters better than 143MHz, so is likely that you'll also be seeing more effects from some of the rather strange bifurcations that can occur. I've seen such effects from the 143MHz carrier wave transmitter of the GRAVES Radar in France and have only come across one paper describing them. If I recall, the author was hypothesising that the cause is due to high altitude wind shear. They are difficult to find in my data, so this example is by far not the best, but gives an example of the bifurcation that you may be seeing. Richard
  3. Well, what can I say? Maybe I just got lucky using an inexpensive SDR, an inexpensive feeder and a simple small 2 element antenna from 1000km away from the radar? However, I've recorded 910 meteor pings today and counting.... Let me clarify for a moment: The less expensive SDR's are definitely not a match for the performance of the Funcube or other high end SDR's. The differences compared to the high end devices include lower dynamic range, lower sensitivity, poorer frequency stability, smaller RF and IF bandwidths and less flexible interface. These are measurable differences. However, my SDR (the one I linked to above) has performed meteor detection admirably a full year, with the only loss of signal due to my own finger trouble, poorly implemented Windows updates and holidays. Perhaps I miss a few scattered signals, but I have a limited common volume due to my range anyway. Perhaps my peak signal to noise is not as high as it could be, but 50db SNR is pretty big on the larger returns. Perhaps the device drifts a few Hz with diurnal variability, but a heatsink attached to the case adds to thermal stability. Perhaps if I wanted to look at the Hydrogen line or Band II signals, I might need better RF bandwidth, but I'm content with the 143MHZ GRAVES Radar. In summary, it's entirely possible there are cheap SDR's that are poorly built, poorly designed and poorly implemented, but I have had no issues with mine, save that the driver will not communicate with Spectrum Lab, but a free third party tool overcame that. £20 for a toe in the water? Got to be worth a shot. Then if the bug bites, or if higher performance is required, perhaps flog it on eBay and invest in a high performance device. You pays you money and all that.... Richard
  4. That's less easy to answer as a lot depends on your location, immediate topography, ground clutter and mounting arrangements (whether inside or outside for example). Since you're in South Essex, it's reasonable to assume you would want either to slightly elevate the antenna, or to have a broad vertical beamwidth if attempting to receive signals from the GRAVES Radar. That being the case, a small yagi would suffice and a quick search online shows plenty of options. This 3 element https://www.radioworld.co.uk/sandpiper-2m---3-element-beam-antenna-5dbd will suffice if you have a clear view, or you may need higher gain by adding a couple of elements, deepening on your situation. If you wanted to make the antenna yourself, there's plenty of diagrams to be found online and it really is as simple as a wooden pole a couple of wire coat hangers cut and bent to the right dimensions and a tuning capacitor. Since you'll only be receiving, you don't need to worry about power coupling and high grade components. I use a 2 element phased array antenna; a so-called HB9-CV design. This yields close to the same forward gain as a 3-element yagi but is physically smaller and easier to mount. I have a pretty clear horizon and mount the antenna on the side of the house, clamped to an old Sky satellite dish mounting bracket. I'm probably 500km further north than you though, so my common volume to the radar is very close to the horizon, whereas yours will be elevated somewhat. Richard
  5. Less expensive SDR's work just as well for meteor detection. This is the SDR I use: https://www.ebay.co.uk/itm/202297427602 currently selling at less than £20. It doesn't match the specification of the Funcube, so may be less flexible to use for other purposes, but as a dedicated meteor detector, it's great. Richard
  6. That's great feedback, much appreciated! Out of interest, is the source for your data online and searchable? It would be interesting to lookup other anomalous objects in the future. Richard
  7. I saw it too Cyril! Amazing sight. I've posted a report in the observations section. Richard
  8. Just seen that post and think it was the same object. It was just one of those incredibly lucky things to be looking in the right direction at the right time. I've witnessed several good displays of noctilucent clouds over the summer while on late night "Dad's taxi duty", but the displays are getting later in the night now and I couldn't stay up after we got home. The bolide was the brightest I've seen and was quite unlike normal meteors. I'd estimate it's velocity to be perhaps half or less that of the classic streaks of light such that "normal" meteors appear as. Still, it was very fast, covering around 1/5th of the elevation of northern sky in a second or so. There was no central plasma trail visible, but it was viewed in the bright afterglow of the sun which was only just below the horizon. There were streamers emanating from the tips of what appeared to be an arc of light on the leading edge and that arc was shimmering, like Venus or Sirius does at low elevations in a scope: almost like a tumbling object showing brighter facets at times. I was looking through the windscreen of the car, so there may have been some aberrations induced by the curved glass and dead bugs. I'll ask my son if the CCTV at the garage captured the object and if it did, if he can obtain a copy of the video. Richard
  9. Hello all, a quick report of a bolide visible over Scotland last night (14th July 2019) at 23:02 local time. I was parked up in a garage forecourt to collect my son from back shift. The car was parked facing almost due north and I was looking towards the northern horizon for noctilucent clouds as the sky was so clear. The lat long location was at 55.7116, -3.8319. The bolide appeared visible through the windscreen of the car. It was travelling a few degrees west of north and was large and relatively slow travelling for a meteor. It had an observable shape, being round and intensely bright, several magnitudes brighter than the nearly full moon behind me. It was yellow-orange with some hint of green at the margins. Towards the southern (lower) portion of the object there appeared to be a partial halo or arc that appeared to shimmer (much like a bright planet low to the horizon through a 'scope). At the tips of this arc there were streams of plasma following the object. The sighting lasted perhaps a second at most before it dissipated in an intense flash. There was no fragmentation that I could see. I first observed it at around 25 degrees above the horizon and lost it at about 10 degrees. The angle of viewing meant it appeared to be heading almost straight "down" towards the horizon. There was no sonic boom that I could hear, even though I had the window of the car wound down. There was passing traffic however, perhaps masking any low rumble. This was very different to the "normal" meteors that one sees, even during the summer months when there are several showers and something that was quite unusual. I've submitted a report to the UK MON this morning and it will be interesting to see if any other lucky amateur astronomers saw the object. Richard
  10. Looking over my meteor detection logs from this morning a rather unusual observation jumped out at me. It appears that I captured two closely orbiting large satellites less than 15 seconds apart. The screen shot below shows the observation at 04:57:50 UTC today 8th July: I'm fairly sure these objects were in orbit due to the slow Doppler shift when compared to the small meteoroid at 04:58:30. My first reaction was that I had captured the ISS and a service craft, but the ISS was nowhere near at that time and there are no service flights that could have generated the second trace a few seconds later. I've had a quick search through a couple of online resources, but am finding it difficult to correlate the time of the observation to any potential candidates. Based on previous observations of the ISS and the zero Doppler shift point of each observation, the objects were likely due south of me, close to my horizon somewhere over the Bay of Biscay and illuminated by the Western facing lobes of the GRAVES RADAR. Initial viewing of the two traces suggests that the Doppler shifts are slightly different, but that may be an optical illusion: more closely inspecting the traces suggests a very similar Doppler shift for each object, starting and completing about 600Hz apart. That in turn suggests a similar orbital height and path. Did anyone else capture these objects or have any suggestions about how to locate what they might be in an online database? Richard
  11. Excellent! It will be fascinating to hear about the development of the system and your correlations against video detected meteors, particularly those over central England versus central or southern France. Have you been able to measure or calibrate the radiation pattern of the array - that will yield important additional information to feed into the cross channel correlations. It is similar, but my contention is that the head echo exhibits a slow speed Doppler shift, suggestive of a sub-orbital speed object as opposed to a meteor travelling perhaps an order of magnitude faster. Do the majority of your captures exhibit a slow head echo? In general, one needs to be a bit careful about the spectral interpretation. With not much resolution presented in the time domain, the trace looks like it has the typical spikes occurring at the phase switching points of the radar array. These spikes are I believe caused by aliasing in the FFT employed in Spectrum Lab. As such, they do not necessarily tell us much about the nature of the object causing the echo or scattering, but indicate the response of the FFT to a high amplitude impulsive change when the transmitter phased array switches. Their presence however does indicate a scattering or reflective medium at a stationary point in the sky, as one would expect from an over dense plasma field. Certainly, I agree that it is an outlier on the SNR chart that you present, and all the more fascinating to understand what it may be. Richard
  12. That's a nice antenna array Mike and could be very useful in calculating further parameters, if you can correlate against known trajectories and signals, for example from the ISS. The orthogonal and vertical components may yield interesting results. The mast head preamps will assist with weak signal detection and overcome feeder loss too. I was perhaps not specific enough when I mentioned space debris. In this context, I meant incoming man-made orbital debris entering the upper atmosphere at sub orbital velocities of maybe 7km/s as opposed to a meteor which may have a velocity of 40-60km/s. The radar itself is presumably tracking orbital parameters of objects in low earth orbit and hence looking for direct scattering off the object itself, such as we might see on the ISS from the radar. However, your observation has a head echo suggestive of low incoming velocity followed by an ionisation trail, which would be reasonable to ascribe to an over-dense field in the ionosphere caused by the incoming object. In other-words, I suspect it was in the atmosphere at a similar altitude to a meteor and not in orbit. Due to the slow Doppler it was possibly not meteroic, but a de-orbiting piece of orbital debris. I don't have the mathematics to verify, but it seems reasonable that the SNR would be related to the intensity of the ionisation and that in turn related to the velocity and mass of the object. All other things being equal, the intensity of the SNR and slow Doppler suggest to me that it was a high mass object entering the upper atmosphere at sub orbital speeds rather than a grain of sand entering at cosmic speeds. Of course, I could be wrong and would be interested in hearing opinions. Richard
  13. I didn't capture that one Mike, but my detector has been offline for a little while as we have been doing some work on the house. Two thoughts come to mind: the Doppler shift on the head echo is slow. Although it's difficult to estimate the absolute velocity from a single observation, in this case, you can clearly see the phase switching every two seconds in the head echo indicating its frequency is changing slowly relative to time. That is suggestive of a slow entry, meaning space debris rather than meteoric. The second thought is related to the location. You speculate it being close to your site, presumably due to the very strong signal to noise ratio. However, if near overhead, your antenna would be unlikely to see a common volume to the GRAVES radar. More likely, is that is is south of the radar and the debris has a large mass resulting in an intense ionisation. This could build upon an already elevated ionisation of the E-layer that occurs during summer months and in particular late June/early July. Sporadic -E propagation can be seeded by incoming debris or meteors and perhaps this was the case here? Richard
  14. I'm working mobile and will be away until sometime on Saturday now, so may not be able to add much detail, but I use a slightly modified (tuned for my setup and site) version of the detection script presented by IanL here:
  15. Yes, that looks very much like the ISS scattering off the western facing frontal lobe. If you can see a pass over central England, that will be really interesting. I made a fascinating observation this evening. I detected what I would characterise as an incoming large piece of space debris. It had the classic head echo caused by the radial velocity Doppler shift, followed by a long tail generated by ionised gas ionosphere. This initially looks like a big meteor, but had a decidedly lower Doppler shift on the head indicating much slower incoming radial velocity. Compare this trace with Stormchaser's detection of a meteor at 21:30 yesterday. The phased switching of GRAVES is visible within the head echo, but the frequency shift is only around 200Hz over about 3 seconds, very roughly the same as I see for satellites and markedly slower than for meteor strikes. Based on the intensity of both the head echo and intensity & duration of the tail it appears that it had a fair amount of mass. Spectrum lab recorded that trace at a peak of 46.7db above noise, some 25db stronger than average detections. Assuming that the ionised tail indicates an altitude in the ionosphere, it appears to have come in somewhere over Southern England, the English Channel or Northern France. It may have been a slightly scary yet very interesting sight had it been dark. Richard
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