5 ms·

I've not read the original report (and am unlikely to), but this quotation: '“WSPR is like a bunch of tripwires or laser beams (graphic below), but they work in

I've not read the original report (and am unlikely to), but this quotation: '“WSPR is like a bunch of tripwires or laser beams (graphic below), but they work in every direction over the horizon to the other side of the globe,” Mr. Godfrey says.' is not an accurate characterization of this (or any) use of WSPR. It implies a degree of precision and clarity of signal that is completely misleading. I'm also very concerned about Godfrey's clear comfort with taking this very weak and contingent signal and using it to ascribe thoughts, motives and behaviour to the aircrew of MH370. You don't do that without substantial corroborating evidence from other sources when you have an intact Cockpit Data Recorder, much less whatever this is. Looks a lot like a familiar pattern: starting with a theory, finding some nice noisy data that needs 'expert interpretation', and then massaging it to confirm your theory.

ellenhp 5y ago
Yeah I'm not an expert in this stuff but I am an extra-class radio amateur and this sets off literally all my intellectual alarm bells. I'll take one for the team and go read the report but I agree that it seems like pure unadulterated bullshit. The ionosphere is a very violent place for an HF radio signal. These radio waves do not travel in a straight line. They don't even come out of the ionosphere with the same polarization as they go in with. I cannot fathom how you could glean anything from a WSPR signal's RSSI. edit 1: I'm just gonna live-text my thoughts on this as I go through it into this comment. First off, the software that this person developed, GDTAAA, doesn't seem to be available for viewing. Shame because I'd love to see it, but I guess I'll have to go by the paper. edit 2: "An algorithm is run that calculates an expected received SNR based on the transmitter power and the short path distance" W O W, okay, not even taking into account an estimated noise for the receiving station. Nice. It also doesn't seem to take into account time of day, any of the different propagation modes like gray line, etc, or the wavelength of the transmission. Big yikes. edit 3: WSPR signals have a transmission length of about two minutes. A 777 travels about 20 miles during that amount of time, and you're trying to use the average SNR of the entire 2 minute period to estimate whether an aircraft crossed the path of the signal. Even if the WSPR signal occupied the entire 20 mile-wide swath of sky that the aircraft was in during the WSPR transmission, the aircraft can only block about 0.2% of that swath at an given moment on account of it being absolutely tiny.
- dboreham 5y ago
  I agree it seems far-fetched, but: possibly by integrating many data samples you can remove the ionosphere noise from an underlying signal.
  - lambdasquirrel 5y ago
    If the ionosphere noise were merely noise, and not just distortion, this would be true. I'd suspect that even changes in solar radiation (from the rotation of the earth) would cause e.g. more ionization in some parts of the ionosphere compared to others.
- jrockway 5y ago
  I'm also an extra-class radio amateur, and I too am unconvinced by this article. The "tripwire" concept looks good in 2D, but I'm less convinced in 3D. Most HF signals propagate by bouncing the signal off the ionosphere (it's actually refraction, not reflection, but...), so the ideal path to the observer looks like shooting a signal straight at the horizon (that's the top of the ionosphere that's farthest from you and not shadowed by the earth). The angle of incidence equals the angle of reflection on the way down, to an ideal receive location where that point that the sender aimed at is where the receiver is aiming at. You can have multiple hops; the ground reflects signal back up towards the sky. (Tangential paper: https://www.physics.princeton.edu//pulsar/K1JT/HFTOA_1.pdf https://www.physics.princeton.edu//pulsar/K1JT/HFTOA_1.pdf You can measure how many hops a signal is taking at any given time, and it changes throughout the day.) So if we were in a "spherical cow" universe, you could see how this would sort of act like a tripwire. A radio transmitter illuminates a single point in the ionosphere, and a radio receiver looks at that point. If a plane flies along that path, the signal goes dark, and you know something crossed your tripwire. The sticky bit is that we aren't operating on points, we're operating on a continuum. If you aim your radio beam at the horizon, maybe 10% of the power is 10 degrees above that, and 5% is 20 degrees above that, and so on. The signal is "smeared" in the real world to the extent that it's not a plane-sized beam that is on or off, rather it's a big circle that gets brighter or dimmer as planes fly through it. And the circle is much, much bigger than any plane. I would be surprised if you'd even notice. (That is assuming an ideal one-hop HF setup. I have never heard of people routinely operating WSPR with an ideal setup, usually people use random wires that have very little directionality to them.) An analogy that you can try right now is getting a camera with a lens that has a large front element (I just tried this with a 90mm f/2.8 lens). Take a picture at the widest aperture. Then stick your big ugly finger in front of the lens, right on the front element, and take another picture. If you look at the second picture, you won't know that your finger was there. There is no obvious finger, or even a finger-shaped shadow. If you compare it to the other picture, maybe you will notice a difference, but maybe you won't. You have to cover a lot of the lens before you notice. (Added fun: consider the 2 minute exposure time of WSPR. Take a picture with a 2 minute exposure time, and walk through the frame midway. Can you see yourself in that picture?) I have to imagine that using WSPR transmitters is a lot like this. If you take lots of samples, maybe a single tiny airplane will make a difference. The data is technically there. But I don't think the random transmitters and receivers are consistent enough across cycles to be able to get this data from a single sample. (Remember that WSPR is 2 minutes transmit and 2 minutes receive. Does your radio heat up and cool down, shifting the frequency of the local oscillator in that interval? Mine certainly does!) As I was reading the article, I thought "neat, but I'm not fully convinced" until I read the part where the author thinks he can do this arbitrarily and detect any airplane at any time, and that it is conveniently done with proprietary software that doesn't show up anywhere on the Internet. That caused the alarm bells to go off. I'm going to need a lot more data to be convinced.
deleted 5y ago
[deleted]
KirillPanov 5y ago
The aircraft detection phenomenon isn't far-fetched sci-fi; here's a video showing what it looks like: https://www.youtube.com/watch?v=1gc0vVk3XBg https://www.youtube.com/watch?v=1gc0vVk3XBg Remember that we're talking about a gigantic hunk of airborne metal, with a mandatory 50 miles of separation from any other gigantic hunk of airborne metal. With that said, the article is claiming to do this detection without the waterfall plot or I/Q data, using nothing but a single scalar data point (receiver SNR) recorded once every two minutes. That is far-fetched sci-fi. If the WSPR stations were archiving the raw I/Q data at the SDR input, I might believe something useful could be recovered from that.
- ellenhp 5y ago
  I mean, sure, measuring occlusion like this is possible in VHF, UHF and beyond. And radar is a real thing that exists, and you can even do passive radar, but to my knowledge you cannot do any of this outside the line of sight of the transmitter and receiver with an object that's only 1-4 wavelengths long. I'd love to be proven wrong because that would be wild and the kind of thing that makes me fall in love with radio all over again, but this source is completely bogus.
  - bmurray7jhu 5y ago
    Over-the-horizon radar uses HF to detect distant objects. See https://en.wikipedia.org/wiki/Over-the-horizon_radar https://en.wikipedia.org/wiki/Over-the-horizon_radar
    - ellenhp 5y ago
      With a big antenna array for beamforming, sure, you can do that. You absolutely cannot do over the horizon radar on 10 watts with two omnidirectional antennas though.
      - jrockway 5y ago
        Wait, who is doing WSPR at 10 watts? Most people are just using an unamplified IO pin off their Raspberry Pi or something; milliwatt at best. (It makes WSPR itself all the more impressive, however!)
greatartiste 5y ago
I can't agree more , reading this every bullsh*t alarm in my brain was triggering. In his report Mr Godfrey never mentions the frequencies used for the WSPR transmissions. This mode can be used on VHF/UHF frequencies where it may reflect from aircraft. But 95% of WSPR transmissions are on frequencies below 30 MHz and most likely below 20 MHz. These have long wavelengths and highly unlikely to be affected by an small (in wavelength terms) aircraft. If it could be affected by aircraft then Mr Godfrey would have to take into account the movement of every aircraft in that region at the time which he doesn't appear to be doing. As a note of explanation I'm a radio amateur and a WSPR station operator , its a brilliant tool for propagation studies but not for this.
- martyvis 5y ago
  > Mr Godfrey would have to take into account the movement of every aircraft in that region I'd imagine there were dozens of aircraft crossing the Indian Ocean around the time MH370 disappeared. If his technique was that good he should be able to demonstrate for any day ending in Y how he can track flight paths compared to ADS-B data from the likes of flightradar24
  - fapjacks 5y ago
    This would be a good rebuttal, to offer up a bunch of counterexamples of transponder data with no corresponding signal in the WSPR "data" using the same method, but also ADS-B transponders are limited in range, so there will be big gaps specifically in the Indian Ocean. But if this (frankly unbelievable) method works well enough to suss out the location of MH370 in those ocean holes then imagine how well it should work in areas saturated with transmitters and receivers. But it won't, because it really sounds like a bunch of hooey.
- femto 5y ago
  I don't disagree with the triggering of your BS alarm, but don't write off the ability of frequencies in the 5-30MHz range to detect an aeroplane the size of a passenger jet. I used to be an engineer on the Jindalee Over-the-Horizon-Radar and it could detect things much smaller than this using these frequencies. Points for and against WSPR detecting MH370: - Jindalee uses huge power: a beamformed antenna transmitting many kW and a beamformed receiver array 3km long (yes, one of the techs who was an amateur did plug his kit into one of the arrays). - Jindalee uses a very stable timebase, meaning it can detect small Doppler shifts. + WSPR has a lot of receivers and transmitters, meaning the target is illuminated from lots of different directions. With the right signal processing, these signals might be synthesised into a large aperture. Are WSPR receivers typically coherent (I/Q)? + According to one article, there are 5000+ WSPR transmitters [1]. If each of these is transmitting 5W (what's typical in your experience?), that's 25kW. A useable power for an OTHR radar. - The WSPRS transmitters have a low duty cycle and are not active simultaneously? + By its nature WSPR will sometimes fluke excellent propagation conditions, meaning it will be able to do things that might otherwise require higher power. With a large number of stations giving N^2 propagation paths, what are the chances of some of them being useable? + An aeroplane the size of MH370 is quite a big target for an HF radar, with quite a big Dopper shift. + By its nature, a received signal will contain information about the channel though which it passed. Minus: chances are this information is filtered out by WSPR's receiver processing. - Does the WSPR database actually store enough information to post process? Ideally it would need to store the sampled waveform from a coherent GPS locked receiver. It looks as if each record is only a received SNR and a drift (presumably a frequency offset) and a timestamp in minutes? - Are WSPR receivers typically GPS locked, meaning they might have the ability to measure small Doppler shifts and be coherently combined with each other? I'd put the possibility of WSPR being able to detect an aeroplane into the "intriguing" category if (huge if) it stored the necessary data in its database. It would be a computational tour-de-force, involving synthesising a large number of WSPR stations into a single aperture, then using that aperture to form bins in range, azimuth and Doppler/velocity, then tracking a target as it moves between bins. Sadly, my guess is that WSPR does not store the necessary data. (Maybe "intriguing" is overstating it. More "wouldn't it be cool if...") [1] https://www.abc.net.au/news/2021-05-05/malaysia-airlines-mh370-series-of-turns-before-disappearing/100116446 https://www.abc.net.au/news/2021-05-05/malaysia-airlines-mh3...
egberts1 5y ago
I am not an expert but one who actually worked on a over-the-horizon radar system. This entire article is predicated on the RF reflectivity of ionosphere being stable during its measurement of computerized triangulation, when in fact that the sky was in sunrise mode where the ionosphere starts to fall to a lower altitude. Such sunrise/sunset transitory phase is never a clean delineation of RF reflection but instead a noisy raster of bounced RF, much like an oversized blanket of aluminum chaff.

ellenhp 5y ago

Yeah I'm not an expert in this stuff but I am an extra-class radio amateur and this sets off literally all my intellectual alarm bells. I'll take one for the team and go read the report but I agree that it seems like pure unadulterated bullshit. The ionosphere is a very violent place for an HF radio signal. These radio waves do not travel in a straight line. They don't even come out of the ionosphere with the same polarization as they go in with. I cannot fathom how you could glean anything from a WSPR signal's RSSI. edit 1: I'm just gonna live-text my thoughts on this as I go through it into this comment. First off, the software that this person developed, GDTAAA, doesn't seem to be available for viewing. Shame because I'd love to see it, but I guess I'll have to go by the paper. edit 2: "An algorithm is run that calculates an expected received SNR based on the transmitter power and the short path distance" W O W, okay, not even taking into account an estimated noise for the receiving station. Nice. It also doesn't seem to take into account time of day, any of the different propagation modes like gray line, etc, or the wavelength of the transmission. Big yikes. edit 3: WSPR signals have a transmission length of about two minutes. A 777 travels about 20 miles during that amount of time, and you're trying to use the average SNR of the entire 2 minute period to estimate whether an aircraft crossed the path of the signal. Even if the WSPR signal occupied the entire 20 mile-wide swath of sky that the aircraft was in during the WSPR transmission, the aircraft can only block about 0.2% of that swath at an given moment on account of it being absolutely tiny.

dboreham 5y ago
I agree it seems far-fetched, but: possibly by integrating many data samples you can remove the ionosphere noise from an underlying signal.
- lambdasquirrel 5y ago
  If the ionosphere noise were merely noise, and not just distortion, this would be true. I'd suspect that even changes in solar radiation (from the rotation of the earth) would cause e.g. more ionization in some parts of the ionosphere compared to others.
jrockway 5y ago
I'm also an extra-class radio amateur, and I too am unconvinced by this article. The "tripwire" concept looks good in 2D, but I'm less convinced in 3D. Most HF signals propagate by bouncing the signal off the ionosphere (it's actually refraction, not reflection, but...), so the ideal path to the observer looks like shooting a signal straight at the horizon (that's the top of the ionosphere that's farthest from you and not shadowed by the earth). The angle of incidence equals the angle of reflection on the way down, to an ideal receive location where that point that the sender aimed at is where the receiver is aiming at. You can have multiple hops; the ground reflects signal back up towards the sky. (Tangential paper: https://www.physics.princeton.edu//pulsar/K1JT/HFTOA_1.pdf https://www.physics.princeton.edu//pulsar/K1JT/HFTOA_1.pdf You can measure how many hops a signal is taking at any given time, and it changes throughout the day.) So if we were in a "spherical cow" universe, you could see how this would sort of act like a tripwire. A radio transmitter illuminates a single point in the ionosphere, and a radio receiver looks at that point. If a plane flies along that path, the signal goes dark, and you know something crossed your tripwire. The sticky bit is that we aren't operating on points, we're operating on a continuum. If you aim your radio beam at the horizon, maybe 10% of the power is 10 degrees above that, and 5% is 20 degrees above that, and so on. The signal is "smeared" in the real world to the extent that it's not a plane-sized beam that is on or off, rather it's a big circle that gets brighter or dimmer as planes fly through it. And the circle is much, much bigger than any plane. I would be surprised if you'd even notice. (That is assuming an ideal one-hop HF setup. I have never heard of people routinely operating WSPR with an ideal setup, usually people use random wires that have very little directionality to them.) An analogy that you can try right now is getting a camera with a lens that has a large front element (I just tried this with a 90mm f/2.8 lens). Take a picture at the widest aperture. Then stick your big ugly finger in front of the lens, right on the front element, and take another picture. If you look at the second picture, you won't know that your finger was there. There is no obvious finger, or even a finger-shaped shadow. If you compare it to the other picture, maybe you will notice a difference, but maybe you won't. You have to cover a lot of the lens before you notice. (Added fun: consider the 2 minute exposure time of WSPR. Take a picture with a 2 minute exposure time, and walk through the frame midway. Can you see yourself in that picture?) I have to imagine that using WSPR transmitters is a lot like this. If you take lots of samples, maybe a single tiny airplane will make a difference. The data is technically there. But I don't think the random transmitters and receivers are consistent enough across cycles to be able to get this data from a single sample. (Remember that WSPR is 2 minutes transmit and 2 minutes receive. Does your radio heat up and cool down, shifting the frequency of the local oscillator in that interval? Mine certainly does!) As I was reading the article, I thought "neat, but I'm not fully convinced" until I read the part where the author thinks he can do this arbitrarily and detect any airplane at any time, and that it is conveniently done with proprietary software that doesn't show up anywhere on the Internet. That caused the alarm bells to go off. I'm going to need a lot more data to be convinced.

deleted 5y ago

[deleted]

KirillPanov 5y ago

The aircraft detection phenomenon isn't far-fetched sci-fi; here's a video showing what it looks like: https://www.youtube.com/watch?v=1gc0vVk3XBg https://www.youtube.com/watch?v=1gc0vVk3XBg Remember that we're talking about a gigantic hunk of airborne metal, with a mandatory 50 miles of separation from any other gigantic hunk of airborne metal. With that said, the article is claiming to do this detection without the waterfall plot or I/Q data, using nothing but a single scalar data point (receiver SNR) recorded once every two minutes. That is far-fetched sci-fi. If the WSPR stations were archiving the raw I/Q data at the SDR input, I might believe something useful could be recovered from that.

ellenhp 5y ago
I mean, sure, measuring occlusion like this is possible in VHF, UHF and beyond. And radar is a real thing that exists, and you can even do passive radar, but to my knowledge you cannot do any of this outside the line of sight of the transmitter and receiver with an object that's only 1-4 wavelengths long. I'd love to be proven wrong because that would be wild and the kind of thing that makes me fall in love with radio all over again, but this source is completely bogus.
- bmurray7jhu 5y ago
  Over-the-horizon radar uses HF to detect distant objects. See https://en.wikipedia.org/wiki/Over-the-horizon_radar https://en.wikipedia.org/wiki/Over-the-horizon_radar
  - ellenhp 5y ago
    With a big antenna array for beamforming, sure, you can do that. You absolutely cannot do over the horizon radar on 10 watts with two omnidirectional antennas though.
    - jrockway 5y ago
      Wait, who is doing WSPR at 10 watts? Most people are just using an unamplified IO pin off their Raspberry Pi or something; milliwatt at best. (It makes WSPR itself all the more impressive, however!)

greatartiste 5y ago

I can't agree more , reading this every bullsh*t alarm in my brain was triggering. In his report Mr Godfrey never mentions the frequencies used for the WSPR transmissions. This mode can be used on VHF/UHF frequencies where it may reflect from aircraft. But 95% of WSPR transmissions are on frequencies below 30 MHz and most likely below 20 MHz. These have long wavelengths and highly unlikely to be affected by an small (in wavelength terms) aircraft. If it could be affected by aircraft then Mr Godfrey would have to take into account the movement of every aircraft in that region at the time which he doesn't appear to be doing. As a note of explanation I'm a radio amateur and a WSPR station operator , its a brilliant tool for propagation studies but not for this.

martyvis 5y ago
> Mr Godfrey would have to take into account the movement of every aircraft in that region I'd imagine there were dozens of aircraft crossing the Indian Ocean around the time MH370 disappeared. If his technique was that good he should be able to demonstrate for any day ending in Y how he can track flight paths compared to ADS-B data from the likes of flightradar24
- fapjacks 5y ago
  This would be a good rebuttal, to offer up a bunch of counterexamples of transponder data with no corresponding signal in the WSPR "data" using the same method, but also ADS-B transponders are limited in range, so there will be big gaps specifically in the Indian Ocean. But if this (frankly unbelievable) method works well enough to suss out the location of MH370 in those ocean holes then imagine how well it should work in areas saturated with transmitters and receivers. But it won't, because it really sounds like a bunch of hooey.
femto 5y ago
I don't disagree with the triggering of your BS alarm, but don't write off the ability of frequencies in the 5-30MHz range to detect an aeroplane the size of a passenger jet. I used to be an engineer on the Jindalee Over-the-Horizon-Radar and it could detect things much smaller than this using these frequencies. Points for and against WSPR detecting MH370: - Jindalee uses huge power: a beamformed antenna transmitting many kW and a beamformed receiver array 3km long (yes, one of the techs who was an amateur did plug his kit into one of the arrays). - Jindalee uses a very stable timebase, meaning it can detect small Doppler shifts. + WSPR has a lot of receivers and transmitters, meaning the target is illuminated from lots of different directions. With the right signal processing, these signals might be synthesised into a large aperture. Are WSPR receivers typically coherent (I/Q)? + According to one article, there are 5000+ WSPR transmitters [1]. If each of these is transmitting 5W (what's typical in your experience?), that's 25kW. A useable power for an OTHR radar. - The WSPRS transmitters have a low duty cycle and are not active simultaneously? + By its nature WSPR will sometimes fluke excellent propagation conditions, meaning it will be able to do things that might otherwise require higher power. With a large number of stations giving N^2 propagation paths, what are the chances of some of them being useable? + An aeroplane the size of MH370 is quite a big target for an HF radar, with quite a big Dopper shift. + By its nature, a received signal will contain information about the channel though which it passed. Minus: chances are this information is filtered out by WSPR's receiver processing. - Does the WSPR database actually store enough information to post process? Ideally it would need to store the sampled waveform from a coherent GPS locked receiver. It looks as if each record is only a received SNR and a drift (presumably a frequency offset) and a timestamp in minutes? - Are WSPR receivers typically GPS locked, meaning they might have the ability to measure small Doppler shifts and be coherently combined with each other? I'd put the possibility of WSPR being able to detect an aeroplane into the "intriguing" category if (huge if) it stored the necessary data in its database. It would be a computational tour-de-force, involving synthesising a large number of WSPR stations into a single aperture, then using that aperture to form bins in range, azimuth and Doppler/velocity, then tracking a target as it moves between bins. Sadly, my guess is that WSPR does not store the necessary data. (Maybe "intriguing" is overstating it. More "wouldn't it be cool if...") [1] https://www.abc.net.au/news/2021-05-05/malaysia-airlines-mh370-series-of-turns-before-disappearing/100116446 https://www.abc.net.au/news/2021-05-05/malaysia-airlines-mh3...

egberts1 5y ago

I am not an expert but one who actually worked on a over-the-horizon radar system. This entire article is predicated on the RF reflectivity of ionosphere being stable during its measurement of computerized triangulation, when in fact that the sky was in sunrise mode where the ionosphere starts to fall to a lower altitude. Such sunrise/sunset transitory phase is never a clean delineation of RF reflection but instead a noisy raster of bounced RF, much like an oversized blanket of aluminum chaff.