7 ms·

I'm not really seeing anything weird with GNSS. I have a continuously-operating receiver that writes its location into a database every second; I did a query o

I'm not really seeing anything weird with GNSS. I have a continuously-operating receiver that writes its location into a database every second; I did a query over the last 30 days and there is no abnormal deviation in position. (My receiver is in a terrible location that can only see a tiny sliver of the sky, and is single-band, so I expect about a +/- 50cm deviation without RTK correction and that's what I'm seeing.) I actually haven't looked at this data for quite a while. I didn't consider the start of the Ukraine war a good reason to start looking at my data, and I delete it after 30 days to save $$$ on block storage. Dumb. (I added some proper downsampling today so I can keep it forever at reasonable cost.) Trusting my own data is always suspicious, so I clicked around randomly on the NYS Spatial Reference Network website (https://cors.dot.ny.gov/ https://cors.dot.ny.gov/; the title of the page is "Shop", but accounts and RTK access are free). They operate a bunch of Continuously Operating Reference Stations and publish statistics about the accuracy. I do see a lot of reported GLONASS cycle slips today. I have no idea if that is normal or not; this is the first time I've ever dug that deeply into station stats. But overall, the position accuracy at the stations I spot-checked are within .5cm, which is normal. (Most use 4 constellations; GPS, GLONASS, Beidou, Galileo; on 2 bands. So even if GLONASS is broken today, one constellation is enough for good accuracy.) If the government has degraded GPS accuracy today as many commenters think have happened, many people would have noticed. The reference stations have known positions; if GPS starts saying they're somewhere else, that's impossible and would be flagged. GPS being significantly degraded would probably be front page news; not just noticed by a few exercise tracking enthusiasts on Reddit. Or maybe it's all a big conspiracy and the US and Russia banded together to hack my database and the NYS spatial reference network. It could happen, I guess, but my non expert opinion is that GPS is fine right now.

mellavora 4y ago
> my non expert opinion Yes, clearly given the detail in your post, you are "not an expert". Thanks for being on HN and making this site great.
- dasv 4y ago
  There is a lot of depth to GNSS! I could do what jrockway did on the grandparent comment and I would not define myself either as anything near an expert on the field.
- jrockway 4y ago
  I think an actual expert would know if those "warnings" are interesting or not. I can find the raw data, but I don't really know what it means ;)
jjwiseman 4y ago
I've been looking at GNSS (mostly GPS, really) interference around the world for a few months. I just generated some maps of the U.S. for the past few days: https://twitter.com/lemonodor/status/1542941996746039297 https://twitter.com/lemonodor/status/1542941996746039297 You can see that there isn't any significant interference visible in the Bay area, or the rest of the United states except for the typical activity in and around military ranges—That huge region in New Mexico experiencing moderate interference is not typical, but seems to correspond with planned testing around White Sands Missile Range, according to an FAA NOTAM[1]. It’s possible that my methodology wouldn’t pick up interference if it’s caused by a low-power jammer or some source of EFI that only has an effect within a few hundred feet. More details on the methodology behind those maps: The ADS-B signals that many aircraft broadcast include not just the aircraft's GPS positions, but also a measure of GPS accuracy (strictly speaking, ADS-B doesn't talk about GPS specifically and can handle any sort of navigation technology; I'm sure there are some planes out there reporting positions based on inertial navigation systems, with correspondingly low accuracy, or GLONASS-derived positions, or whatever, but my understanding is that right now something on the order of 99% of aircraft with ADS-B are using good old GPS so I'll just keep using the term GPS in this description). If you go to https://globe.adsbexchange.com https://globe.adsbexchange.com and click on just about any aircraft, you'll see an info sidebar on the left of the screen. Scroll down until you see the ACCURACY section, and you'll see values labeled NACp, SIL, NACv, NICbaro, and Rc. Those are all self-reported measures of the accuracy of the data being sent by the aircraft[2]. NACp is "Navigation Accuracy Category for position", and is a good measure of whether the aircraft's GPS is working well. (A somewhat obscure feature of ADS-B Exchange lets you see a map of all aircraft that are currently reporting poor navigation accuracy for their GPS: https://globe.adsbexchange.com/?badgps https://globe.adsbexchange.com/?badgps) To make the maps, I process a day's worth of data from ADS-B Exchange to find all the aircraft reporting poor navigation accuracy and then I color map hexes (using H3 hexes) according to the proportion of aircraft passing through that hex that reported bad GPS accuracy. Specifically, I'm counting an aircraft as experiencing "interference" if it at some point reported good navigation accuracy and then reported low accuracy. Doing this helps filter out aircraft that just have an ongoing issue with their GPS equipment, or don't even have GPS. When I do that, areas where there is systematic interference—almost always jamming by military systems—become obvious. There are a few conflict zones (Syria, Cyprus, Israel) that have been experiencing jamming for years, and the U.S. often has smaller scale military testing, especially in the West and Southwest. You can also see the jammers that are apparently setup around Moscow to prevent drones from flying near Oligarch dachas[3]. I started making these maps in February before Russia invaded Ukraine because I thought it might provide an early warning of an invasion. I didn't see that, and in fact this technique doesn't do a very good job of mapping GPS jamming around the actual war zones because civil aviation stopped over Ukraine, so there are zero or few aircraft with ADS-B reporting their GPS accuracy[4]. Without that data, I can't make a map. Sometimes I do see changes, like when Russia suddenly started jamming around Kaliningrad in March 2022, causing interference in many Baltic states and leading to Finland to cancel some flights[5]. Then a few days later, they just stopped. [Edit:] I don't think too many people have realized yet what an amazing source of GPS interference data is available using ADS-B! It's like having thousands of sensors roaming the planet, broadcasting GPS accuracy data every few seconds. I sometimes wonder if I would disrupt someone's nascent business model if I started publishing my maps regularly. (I have a Synology setup with 12 TB that I use to store various sensor data—I highly recommend it.) 1. https://www.faasafety.gov/files/notices/2022/Jun/WSMRNM_22-07_GPS_Flight_Advisory_Revision_2.pdf https://www.faasafety.gov/files/notices/2022/Jun/WSMRNM_22-0... 2. https://twitter.com/lemonodor/status/1493789598077440000 https://twitter.com/lemonodor/status/1493789598077440000 3. https://www.gpsworld.com/jammers-at-dachas-add-to-russias-ability-to-silence-gps/ https://www.gpsworld.com/jammers-at-dachas-add-to-russias-ab... 4. https://twitter.com/lemonodor/status/1497295859196649475 https://twitter.com/lemonodor/status/1497295859196649475 5. https://twitter.com/lemonodor/status/1500719113185816577 https://twitter.com/lemonodor/status/1500719113185816577

mellavora 4y ago

> my non expert opinion Yes, clearly given the detail in your post, you are "not an expert". Thanks for being on HN and making this site great.

dasv 4y ago
There is a lot of depth to GNSS! I could do what jrockway did on the grandparent comment and I would not define myself either as anything near an expert on the field.
jrockway 4y ago
I think an actual expert would know if those "warnings" are interesting or not. I can find the raw data, but I don't really know what it means ;)

jjwiseman 4y ago

I've been looking at GNSS (mostly GPS, really) interference around the world for a few months. I just generated some maps of the U.S. for the past few days: https://twitter.com/lemonodor/status/1542941996746039297 https://twitter.com/lemonodor/status/1542941996746039297 You can see that there isn't any significant interference visible in the Bay area, or the rest of the United states except for the typical activity in and around military ranges—That huge region in New Mexico experiencing moderate interference is not typical, but seems to correspond with planned testing around White Sands Missile Range, according to an FAA NOTAM[1]. It’s possible that my methodology wouldn’t pick up interference if it’s caused by a low-power jammer or some source of EFI that only has an effect within a few hundred feet. More details on the methodology behind those maps: The ADS-B signals that many aircraft broadcast include not just the aircraft's GPS positions, but also a measure of GPS accuracy (strictly speaking, ADS-B doesn't talk about GPS specifically and can handle any sort of navigation technology; I'm sure there are some planes out there reporting positions based on inertial navigation systems, with correspondingly low accuracy, or GLONASS-derived positions, or whatever, but my understanding is that right now something on the order of 99% of aircraft with ADS-B are using good old GPS so I'll just keep using the term GPS in this description). If you go to https://globe.adsbexchange.com https://globe.adsbexchange.com and click on just about any aircraft, you'll see an info sidebar on the left of the screen. Scroll down until you see the ACCURACY section, and you'll see values labeled NACp, SIL, NACv, NICbaro, and Rc. Those are all self-reported measures of the accuracy of the data being sent by the aircraft[2]. NACp is "Navigation Accuracy Category for position", and is a good measure of whether the aircraft's GPS is working well. (A somewhat obscure feature of ADS-B Exchange lets you see a map of all aircraft that are currently reporting poor navigation accuracy for their GPS: https://globe.adsbexchange.com/?badgps https://globe.adsbexchange.com/?badgps) To make the maps, I process a day's worth of data from ADS-B Exchange to find all the aircraft reporting poor navigation accuracy and then I color map hexes (using H3 hexes) according to the proportion of aircraft passing through that hex that reported bad GPS accuracy. Specifically, I'm counting an aircraft as experiencing "interference" if it at some point reported good navigation accuracy and then reported low accuracy. Doing this helps filter out aircraft that just have an ongoing issue with their GPS equipment, or don't even have GPS. When I do that, areas where there is systematic interference—almost always jamming by military systems—become obvious. There are a few conflict zones (Syria, Cyprus, Israel) that have been experiencing jamming for years, and the U.S. often has smaller scale military testing, especially in the West and Southwest. You can also see the jammers that are apparently setup around Moscow to prevent drones from flying near Oligarch dachas[3]. I started making these maps in February before Russia invaded Ukraine because I thought it might provide an early warning of an invasion. I didn't see that, and in fact this technique doesn't do a very good job of mapping GPS jamming around the actual war zones because civil aviation stopped over Ukraine, so there are zero or few aircraft with ADS-B reporting their GPS accuracy[4]. Without that data, I can't make a map. Sometimes I do see changes, like when Russia suddenly started jamming around Kaliningrad in March 2022, causing interference in many Baltic states and leading to Finland to cancel some flights[5]. Then a few days later, they just stopped. [Edit:] I don't think too many people have realized yet what an amazing source of GPS interference data is available using ADS-B! It's like having thousands of sensors roaming the planet, broadcasting GPS accuracy data every few seconds. I sometimes wonder if I would disrupt someone's nascent business model if I started publishing my maps regularly. (I have a Synology setup with 12 TB that I use to store various sensor data—I highly recommend it.) 1. https://www.faasafety.gov/files/notices/2022/Jun/WSMRNM_22-07_GPS_Flight_Advisory_Revision_2.pdf https://www.faasafety.gov/files/notices/2022/Jun/WSMRNM_22-0... 2. https://twitter.com/lemonodor/status/1493789598077440000 https://twitter.com/lemonodor/status/1493789598077440000 3. https://www.gpsworld.com/jammers-at-dachas-add-to-russias-ability-to-silence-gps/ https://www.gpsworld.com/jammers-at-dachas-add-to-russias-ab... 4. https://twitter.com/lemonodor/status/1497295859196649475 https://twitter.com/lemonodor/status/1497295859196649475 5. https://twitter.com/lemonodor/status/1500719113185816577 https://twitter.com/lemonodor/status/1500719113185816577