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About Geminids

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    Hayfield, Derbyshire
  1. I know I'm a bit late with this reply (as a new comer looking at the old posts ) but back in 2016 I did some comparisons of ISS records for a number of radio observers from Rebublic of Ireland to the West, Licolnshire to the East, Hampshire to the South and Derbyshire to the North. I made some notes at the time and as I am a pictures man there are plots but not many words. I hope pdfs work here Method and Final results.pdf ISS Transit Times 20160729.pdf PS If any of the initials are recognised then hallo chaps - I will mention your names if you want me to.
  2. Good work James. You seem to have removed any moon echoes which I assume you get. I had large counts which needed to be filtered out form the results. I think my results look quite similar albeit upside-down to yours. I am a fiddler so that accounts for the gaps in my data The BAA handbook gives ZHR at maximum of 15. Don't know if the ZHR is for visual observers - anyone know? Even with the background non-stream "sporadics" of uo to 25 there are still some hotspots of activity some 40 counts per hour above this.
  3. Thanks IanL for the reply and your useful notes on Head Echoes. Interestingly another way of looking at the Doppler shift is using the Wikipedia definition for bistatic Doppler which gives DeltaF = (1/lambda) . d(RG + RM)/dt where DeltaF is the frequency shift, lambda is wavelength, RG and RM are the ranges of moving body from GRAVES and the monitor station respectively. Thus d(RG + RM) / dt is rate of change of the sum (RG + RM). Although I haven't done the algebra I am sure they are different formualtions of the same physics. Wikipedia notes also notes under bistatic Doppler "... that objects moving along the line connecting the transmitter and receiver will always have 0 Hz Doppler shift ..." By this I infer that DeltaF will be zero when crossing over the Great Circle between GRAVES and Monitor station. This could at least give a line over which the meteoroid has passed So, choosing a nice round figure for the actual velocity of the meteoroid of say 24 km/s the detected signal would last about a quarter of a second. I too, very many versions away, started my Conditional Action scripts on those of Paul Hyde. For Head echoes I have modified my most recent incarnation to capture a screen shot whenever the rate of change of the frequency (DeltaF/dT) is above a given amount. Measuring this frequency slope has been identified in recent IMO journal articles: "Forward Scattering : an interesting formula to calculate the velocity of a meteoroid that generates a head echo"; Pierre Ernotte; WGN, the Journal of the IMO 46:6 (2018) pp 198 and the subsequent paper " Visualizing sporadic meteor radiants and their dynamics by radio forward scattering"; Wolfgang Kaufmann; WGN, the Journal of the IMO 46:6 (2018) pp 201. I needed to modify the size of the FFT to increase the Spectrogram scroll rate and improve time resolution (at the expense of frequency resolution) I am still playing with this so won't give any details at the moment, but here is a typical screenshot. I have been able to extract the frequency and time data from pixel data of images using software and have sensible figures for the frequency slope albeit with wide uncertainties. The software gives me 20 ms per pixel on the time axis and just over 2 Hz per pixel on the frrequency axis. My spectrogram indicates 2000 Hz corresponding to zero Doppler and the GPSDO on the RSPDuo ensures confidence in the absolute frequency. In a roughly 24 hour period I captured some 1000 screen shots of which 50 were of the kind of quality that would allow slope extraction, and so it can be seen that I need to improve matters quite a bit to get the right ones The software will probably allow me to automatically extract the details but not sure yet. I also am working on getting a log of the frequency and time down the slope.
  4. I have been thinking about what to expect for a head echo and what measurement requirements one might need. Very much rule of thumb so comments very welcome. Kaufmann has written a paper in IMO's WGN 46:6 (2018) where he shows what he calls the "frequency slope" by which I think he is referring to the rate of change of Doppler frequency with time - dF/dT. His figures vary from around 250 Hz/s to 10kHz/s. Meteoroids may have velocities of say 60km/s to say 20km/s and 40km of atmosphere (110 to 70km) to pass through (this is a gross approximation as meteoroid direction and locations come into the calculation but we don't know these). The duration of the head echo, if it is strong enough scatter, will be 0.75 to 2 seconds. In this time the frequency recorded could have shifted by a few thousand Hz. To resolve this we would need to get from our Spectrogram / FFT to provide frequency, say, every 100 Hz . This would correspond to 2000 / 100 or 20 frequency samples. To do this in our one or two second time frame means readings every 50ms to 100ms. As I said , very much rule of thumb and could be completely wrong. What do you think? Mike
  5. Hallo group and in particular Richard. I have been programming SpectrumLab CA scripts and configurations unsuccessfully to extract the frequency slope of the head echo. I have tried detecting when a head echo has occurred and capturing a screen shot to measure. I have also tried using a CA script to write a log file for the progressing frequency slope. I fortuitously captured one spectrogram image that I could measure but to me the time resolution appears to be am issue. I have logged a hand full of head echoes to text files but not succeeded in getting the full stroke, I assume because of the resolution ? I am very keen on extracting this data and would welcome a chat, perhaps by email.
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