Great explanation of gps!. At the end you talk about the jamming. It is reported recently that gps signal close to war zones are jammed. So if you decide to replace the ILS at airport you fully depend on GPS and when that is jammed, you have noting... So as a backup keeping ILS? Or go for MLS, a system that was developed as successor of ILS but was passed by GPS technology. MLS requires less ground equipement that ILS and allows for curved approaches.
@@falxonPSN MLS: Microwave Landing System. It works with much higher frequencies and as I already mentioned, it enables curved approaches instead of the strait ones on the ILS.
In my work we use GPS for microsecond-accurate timing. Years ago we did some work with vehicle tracking and I did some tests driving around town. GPS could tell me what road I was on. Differential GPS (an early augmentation system intended for ships) could tell me what lane I was in. We also had a spot in our parking lot surveyed to continental drift accuracy so we could make sure our software was working. In the air? Bad Elf and ForeFlight. WAAS fix accuracy less than my plane's wingspan. Excellent!
The "fun fact" that the first precision GPS was installed at Bremen Airport could perhaps be explained by the fact, that the prime contractor for the development of the European Galileo System is a Bremen based aerospace company (not Airbus Defence and Space, though ... ).
Great video! Will you be making an audio version of your book? I would love to listen to your wisdom on my way to work! Thank you for all that you do, Captain Joe.
The relativistic effect of the Earth's gravity on the surface compared to at the altitude of the satellites is also considered as this affects how the clocks measure time.
No, since the position is determined by differentiating the signals and all satellites are roughly on the same orbital shell this effect cancels out. That said if there’s a need to correct the clock on a satellite it has to be taken into account. Btw. since the increased distance from earth speeds up time and the speed of the satellites slows down time there is an orbit where both effects cancel each other out, but it’s much lower and therefore many more satellites would have been necessary for the system.
@@LisztyLisztFirst I did mention that the reduced gravity has an effect, second each satellite is moving with almost 4km/s so there is relativistic time dilation Mr. „look it up“.
@@mirador698 You're tripping over yourself now, mate. You're either agreeing with my OP, or you're not. You can't do both. Who do you think you are? Jordan Peterson?
@@LisztyLiszt It's wrong because although the effects are there all satellites are affected (almost) equally and therefor relativity can be neglected calculating the receivers position. That said if I want to set my local clock using the GPS time I'd have to correct for relativistic effects. The first application uses relative time differences, the latter absolute time with a shifted reference frame.
I remember growing up in 90s and plugging a GPS receiver into a laptop for car navigation (and it constantly getting "lost" due to the low accuracy from selective availability).
Yup, i remember using "AutoRoute" on an old Win95 486 laptop and navigating through Tennessee USA. It worked great, for as long as you had battery life !. I then got one of the very first TomTom's. They look tiny now compared to current stuff.
Does the system give your altitude as well or just a position on a two dimensional map, with altitude derived from map data? You've already answered it. Sorry for my impatience. Great video.
Could you explain what waypoints are? I learned about them watching a 3 part Documentary called " City in the Sky." I thought it would be a fun for you to make a video about them.
Only problem of GPS is in case of jamming or even worse spoofing. As in first case you can't use GPS and revert to other systems. With spoofing you may thing it's working when in teality isn't.
Is GPS integrated with the Flight Director and the autopilot? Do you just plug in the coordinates for your destination and it will take the plane there, and land it as well?
There is a database in the aircraft’s flight management system which stores the coordinates of all airports, navaids etc. So yes on paper you can tell the aircraft to directly go to the airport. But no it wouldn’t land the plane.
I have heard that the GPS signal from the satellites also has to be corrected for the slight difference in time due to the weaker gravity at a distance from the Earth. Is this correct?
Captain, those GPS required electricity. We rely on it too much that makes us lazy to read a map or other methods of navigation. Perhaps you should talk about a movie called ' rescue flight 771'. It's a good movie, should be recommended for today's flyers.
I was hoping to hear a segment on how incredibly weak the GPS signals are, and how we can only receive them with some clever processing technique (PRN codes and correlators).
WAC charts may be used for visual flights only. Even so, nowadays most pilots would use digital versions of visual charts in iPads or similar devices. In my days (long gone), I used paper WAC and sectional charts for both flight planning and inflight use, but for visual flights only. For IFR, other types of charts are used. Again, in paper form back in the day and in digital representation nowadays.
The explanation of how GPS works was good, but not ideal. While the satellites have extremely precise atomic clocks, your GPS receiver has a CASIO (a normal quartz clock). Not nearly good enough to mess with the speed of light. The explanation said that you need 3 satellites or the coordinates and the 4th satellite to correct the GP receiver's clock. That was a better "dumbing down" than what most explanations do which is to just ignore this fact and say that you re receiver "knows" the time and directly measures the time it takes the signal to arrive from the the satellite to the receiver. But is still dumbing down. Here is how it works and I will explain it in 3 different ways: 1: You start by assuming that your receiver's clock is accurate. When you get the info from 3 satellites (A, B and C), you get 3 "spheres" (distances from each satellite given by the assumed time it took the signal to travel from each of them to you) and the 3 spheres intersect in one point, let's call it ABC (actually two but one is outside of the satellite's orbits and it is discarded). When you bring the 4th satellite D, you get 3 new points: ABD, BCD and ACD. And guess what? The 4 points will not match because your assumption that your receiver's clock is accurate is wrong. Ok, so if your clock is not accurate, it has an error. Wouldn't it be great to know what this error is so you can just correct your clock and make the 4 points land in the same place? Well, you can just adjust your clock until the 4 points are identical (or at least until you get a minimum between the 2 most distant points), and that's what the GPS does. Now, note, as you adjust your clock, all 4 points will change because all 4 spheres will change. So it's not really that the 4th satellite is used to "correct the clock". All 4 are used to correct the clock, and to let you get the correct coordinates. 2: Your CASIO watch is not extremely precise in the long term, like to keep time, but it is precise enough to measure very short time periods, like milliseconds. So when you receive the signal from satellite A saying "Hi, this is A, it's 12:00:00.000 I am at position A" and, one millisecond later, you receive the signal from B saying "Hi, this is A, it's 12:00:00.000 I am at position B" you don't know at what exact time you receives these messages, so you don't know the distance to either A or B, but you know that you are 1 light-millisecond farther away from B than from A. That doesn't give you a sphere, it gives you a hyperboloid, let's call it AB. But it doesn't matter, you still need the intersection of 3 of those to get a coordinate. But note how, unlike the sphere which belonged to one satellite, the hyperboloid belongs to two? So to get the coordinate you need 4 satellites to give you 3 hyperboloids. AB, BC, DC and DA (no guys, the AC hyperboloid doesn't help because it doesn't add any new information, like if I tell you X+Y=2, "oh and by the way 2X+2Y=4" doesn't help you an inch to find X and Y). Now with the 3 hyperboloids your can get your exact location and, as a bonus, you now can calculate your true distance to any of the satellites and hence the time it takes the signal to arrive, which let's get an accurate time too. 3: Spacetime is 4-dimensional (3 dimensions of space and 1 of time). You just need four 4-coordinates points (the 4 satellites saying "I am here in space and time") to solve for your own 4 coordinates (space and time). This is not different than 1 and 2. In fact, 1 and 2 are just two different, but mathematically equivalent, approaches to solve this system of 4 unknowns in 4 equations. Finally, the system is not perfect. The satellites are not EXACTLY where they "think" they are, nor is their time EXACTLY what they think it is, plus the radio signals gets distorted in the atmosphere in ways that are not EXACTLY the way we predict they will, and our receivers are not perfect either. Because of this, 4 satellites don't give you your EXACT position (and nothing will). Adding more than satellites will let your device find the point that minimizes the overall error and say "THIS is your point" with much better accuracy than using just 4 satellites. So that's what receivers do. And then the error detection by space and ground stations being broadcasted to receivers (used only by advanced receivers like SOME aviation GPS systems) so they can correct for those errors makes the precision even one or 2 orders of magnitude better. A GPS-guided missile can literally go to a specific window of a specific building, if you know the coordinates of that window with enough precision. And that's actually the Achilles's heel of the system. It can be used for good or evil. Imagine an ideal John Lennon's world with no evil, then we would not need 4 satellite systems (USA, EU, Russia and China), we could pout all the resources into making only one system much better, and we could make the full accuracy free to everybody, and not be worried about the US (or another actor) "turning it off" in times of war, or with Russia jamming it in times of war. So we cannot relay ONLY in GPS for critical things.
Gee , I thought that the GPS WAS a little lady in the phone . You spoilt my vision , the lady in my Gps isn't that accurate, I always go on guided tour , because I don't have a tape measure that goes 500 meters. So how does it work . With a plane, please turn left at the big fluffy cloud, 😅😂 stuff it !! The wind blew and the cloud isn't that fluffy , ok so we're going via world tour , to America . Buckle up we're in for a long ride . Now work out how much petrol you will need . 😂😂
So fog horns work, because the earth is flat. So there it is, the Captain said it. /s of course. Sound also travels (in general) in 3 dimensions. But in the local environment, where the sound can be picked up, it can be assumed that the change of elevation due to curvature of Earth is not that significant.
Can someone please explain: Joe still only has 3 stripes, that means he is no captain right?? How long does it take to become a captain, feel like Joe has enough experience.
Command depends on seniority more than experience. Plus the approx timeframe for someone to become an airline captain differs from place to place. Could be as low as 3 years, could be as much as 10+ years.
When there was no GPS, how a pilot knew the destination position? Moreover, during world war II, pilots I am sure flew the propeller planes without GPS. Thus, how did they know the destination position?
Before GPS you had ground navigation aids. And before that you had a dedicated navigator whose task was to know where you are using stars and other references.
Why isn't Galileo mentioned? Or asked differently, why europeans arent pushing for navigation with Galileo since they wanted their own GPS system that would be independent of the U.S.'?
Galileo Is mentioned as one gnss systems at beginning of video... Then you can just refer to generic GPS for it's work and that is valid for Galileo as well
I am not so sure if gps should be the future for precision approaches. Recently interference with gps signals (jamming and spoofing) has sharply increased. Also the war in Ukraine shows these shortcomings as EW (electronic warfare) renders gps pretty much useless. Russian ew in Königsberg/ kaliningrad poses risks and problems to civil aviation in a larger area in Europe.
@@NoHandleToSpeakOf not sure of that but I read somewhere that upto Mauritius there is a reach. But still he said list of navigation system. It is not like who is using it.
Yes, please a video on jamming and spoofing!
I also see a huge jeopardy for aviation in this. I think, having always a "plan B" is important!
Best explanation of GPS that I have seen
Great explanation of gps!. At the end you talk about the jamming. It is reported recently that gps signal close to war zones are jammed. So if you decide to replace the ILS at airport you fully depend on GPS and when that is jammed, you have noting... So as a backup keeping ILS? Or go for MLS, a system that was developed as successor of ILS but was passed by GPS technology. MLS requires less ground equipement that ILS and allows for curved approaches.
This would be a good video topic for sure. I'm an aviation enthusiast and thought I knew most of the basics but I had never heard of MLS until now.
@@falxonPSN MLS: Microwave Landing System. It works with much higher frequencies and as I already mentioned, it enables curved approaches instead of the strait ones on the ILS.
The technical subjects are the videos I've missed the most, Joe! Mehr bitte!
In my work we use GPS for microsecond-accurate timing. Years ago we did some work with vehicle tracking and I did some tests driving around town. GPS could tell me what road I was on. Differential GPS (an early augmentation system intended for ships) could tell me what lane I was in. We also had a spot in our parking lot surveyed to continental drift accuracy so we could make sure our software was working.
In the air? Bad Elf and ForeFlight. WAAS fix accuracy less than my plane's wingspan. Excellent!
What is Bad Elf? Foreflight?
@@Seventh7Art Portable GPS. Flight planning software.
Missed your videos Captain Joe for a long time. Thanks for coming back.
1:42 since you are naming them all, you could clarify that a correct name for GPS is Navstar.
CFII here, I learned alot from this video! Will definitely use the fog horn explanation when teaching students thanks Joe!
Epic Video. I'd watch a Captain Jeo Video over Netflix Anyday!🙂 A Video On Jamming will be very informative captain 🙂
Super good example with the airhorns.
Small correction.
SBAS stands for "satelite based augmentation system" and not "space..."
Cheers
Captain/instructor Joe is back!💕🙏
There are also GPS almanac which is data with coarse GPS orbits and A-GPS which is assist for faster fix with the help of mobile network.
Hands up for GPS spoofing videos 🙌🏽
The "fun fact" that the first precision GPS was installed at Bremen Airport could perhaps be explained by the fact, that the prime contractor for the development of the European Galileo System is a Bremen based aerospace company (not Airbus Defence and Space, though ... ).
Great video! Will you be making an audio version of your book? I would love to listen to your wisdom on my way to work! Thank you for all that you do, Captain Joe.
A very clear explanation regarding the complexities of GPS - thank you.
The video was super helpful with the examples, very well explained, just great 👍
My birthday came early this month. A captain joe video!
That was a great explanation Captain
Love it. Thank you Joe.
Nice one Joe. Cheers from Australia.
First class explanation :)
This is just fascinating in so many ways.
The relativistic effect of the Earth's gravity on the surface compared to at the altitude of the satellites is also considered as this affects how the clocks measure time.
No, since the position is determined by differentiating the signals and all satellites are roughly on the same orbital shell this effect cancels out. That said if there’s a need to correct the clock on a satellite it has to be taken into account.
Btw. since the increased distance from earth speeds up time and the speed of the satellites slows down time there is an orbit where both effects cancel each other out, but it’s much lower and therefore many more satellites would have been necessary for the system.
@@mirador698 It's not about speed, it's about gravity. Look it up.
@@LisztyLisztFirst I did mention that the reduced gravity has an effect, second each satellite is moving with almost 4km/s so there is relativistic time dilation Mr. „look it up“.
@@mirador698 You're tripping over yourself now, mate. You're either agreeing with my OP, or you're not. You can't do both. Who do you think you are? Jordan Peterson?
@@LisztyLiszt It's wrong because although the effects are there all satellites are affected (almost) equally and therefor relativity can be neglected calculating the receivers position.
That said if I want to set my local clock using the GPS time I'd have to correct for relativistic effects. The first application uses relative time differences, the latter absolute time with a shifted reference frame.
Captain Joe explained it very clearly.
Nice information Sir
great video, thanks
Very useful information
Cap thanks
GPS JAMMING AND SPOOFING IS THAT LIKE DANCE PARTY IN THE GPS.
HEAVEY ROCK 😅😂🎉
I would be interested in an episode on jamming and spoofing.
I am reminded of the Inglorious Bastards, when I see Captain signs the number 3 with his fingers.
I remember growing up in 90s and plugging a GPS receiver into a laptop for car navigation (and it constantly getting "lost" due to the low accuracy from selective availability).
Yup, i remember using "AutoRoute" on an old Win95 486 laptop and navigating through Tennessee USA. It worked great, for as long as you had battery life !. I then got one of the very first TomTom's. They look tiny now compared to current stuff.
🙏 Thanks 🙏 my 🙏 🙏 teacher 🙏
thank you captain !
Thank you!
thankyou captain
Excellent!
Here's something worth covering: the inertial navigation/reference system. which will come in handy when GPS becomes inoperative.
Does the system give your altitude as well or just a position on a two dimensional map, with altitude derived from map data? You've already answered it. Sorry for my impatience. Great video.
Now waiting for that jamming and spoofing videooo
Could you explain what waypoints are? I learned about them watching a 3 part Documentary called " City in the Sky." I thought it would be a fun for you to make a video about them.
Best "how to" on YT.
Only problem of GPS is in case of jamming or even worse spoofing. As in first case you can't use GPS and revert to other systems. With spoofing you may thing it's working when in teality isn't.
Could you maybe do 747 MSFS tutorials in the future? Anyways great vid
Can you make a live stream on one of your Cargolux flight
Is GPS integrated with the Flight Director and the autopilot? Do you just plug in the coordinates for your destination and it will take the plane there, and land it as well?
There is a database in the aircraft’s flight management system which stores the coordinates of all airports, navaids etc. So yes on paper you can tell the aircraft to directly go to the airport. But no it wouldn’t land the plane.
Hi Captain, could you say whether GPS (or EGNOS) gives vertical information as well as lateral information on an approach?
I have heard that the GPS signal from the satellites also has to be corrected for the slight difference in time due to the weaker gravity at a distance from the Earth. Is this correct?
Thanks after a long received such a interesting video on operational feature
Captain, those GPS required electricity. We rely on it too much that makes us lazy to read a map or other methods of navigation. Perhaps you should talk about a movie called ' rescue flight 771'. It's a good movie, should be recommended for today's flyers.
I was hoping to hear a segment on how incredibly weak the GPS signals are, and how we can only receive them with some clever processing technique (PRN codes and correlators).
Pun at 0:56 anyone?
Excellent explanation of GPS navigation. Sailor and private pilot here.
Want to know about the jamming and spoofing threat. There is a lot of trouble currently with that...
You should have watched the video to the end.
at siemens product's was "R" to read !
gpRs ...somebody told me it is for the word➡️ Routing
bad visibility , well what is about bird's in fog ?
Capt., do pilots plan their flight/routes using WAC maps? Or you already do it thru a computer?
WAC charts may be used for visual flights only. Even so, nowadays most pilots would use digital versions of visual charts in iPads or similar devices. In my days (long gone), I used paper WAC and sectional charts for both flight planning and inflight use, but for visual flights only. For IFR, other types of charts are used. Again, in paper form back in the day and in digital representation nowadays.
The explanation of how GPS works was good, but not ideal. While the satellites have extremely precise atomic clocks, your GPS receiver has a CASIO (a normal quartz clock). Not nearly good enough to mess with the speed of light. The explanation said that you need 3 satellites or the coordinates and the 4th satellite to correct the GP receiver's clock. That was a better "dumbing down" than what most explanations do which is to just ignore this fact and say that you re receiver "knows" the time and directly measures the time it takes the signal to arrive from the the satellite to the receiver. But is still dumbing down. Here is how it works and I will explain it in 3 different ways:
1: You start by assuming that your receiver's clock is accurate. When you get the info from 3 satellites (A, B and C), you get 3 "spheres" (distances from each satellite given by the assumed time it took the signal to travel from each of them to you) and the 3 spheres intersect in one point, let's call it ABC (actually two but one is outside of the satellite's orbits and it is discarded). When you bring the 4th satellite D, you get 3 new points: ABD, BCD and ACD. And guess what? The 4 points will not match because your assumption that your receiver's clock is accurate is wrong. Ok, so if your clock is not accurate, it has an error. Wouldn't it be great to know what this error is so you can just correct your clock and make the 4 points land in the same place? Well, you can just adjust your clock until the 4 points are identical (or at least until you get a minimum between the 2 most distant points), and that's what the GPS does. Now, note, as you adjust your clock, all 4 points will change because all 4 spheres will change. So it's not really that the 4th satellite is used to "correct the clock". All 4 are used to correct the clock, and to let you get the correct coordinates.
2: Your CASIO watch is not extremely precise in the long term, like to keep time, but it is precise enough to measure very short time periods, like milliseconds. So when you receive the signal from satellite A saying "Hi, this is A, it's 12:00:00.000 I am at position A" and, one millisecond later, you receive the signal from B saying "Hi, this is A, it's 12:00:00.000 I am at position B" you don't know at what exact time you receives these messages, so you don't know the distance to either A or B, but you know that you are 1 light-millisecond farther away from B than from A. That doesn't give you a sphere, it gives you a hyperboloid, let's call it AB. But it doesn't matter, you still need the intersection of 3 of those to get a coordinate. But note how, unlike the sphere which belonged to one satellite, the hyperboloid belongs to two? So to get the coordinate you need 4 satellites to give you 3 hyperboloids. AB, BC, DC and DA (no guys, the AC hyperboloid doesn't help because it doesn't add any new information, like if I tell you X+Y=2, "oh and by the way 2X+2Y=4" doesn't help you an inch to find X and Y). Now with the 3 hyperboloids your can get your exact location and, as a bonus, you now can calculate your true distance to any of the satellites and hence the time it takes the signal to arrive, which let's get an accurate time too.
3: Spacetime is 4-dimensional (3 dimensions of space and 1 of time). You just need four 4-coordinates points (the 4 satellites saying "I am here in space and time") to solve for your own 4 coordinates (space and time). This is not different than 1 and 2. In fact, 1 and 2 are just two different, but mathematically equivalent, approaches to solve this system of 4 unknowns in 4 equations.
Finally, the system is not perfect. The satellites are not EXACTLY where they "think" they are, nor is their time EXACTLY what they think it is, plus the radio signals gets distorted in the atmosphere in ways that are not EXACTLY the way we predict they will, and our receivers are not perfect either. Because of this, 4 satellites don't give you your EXACT position (and nothing will). Adding more than satellites will let your device find the point that minimizes the overall error and say "THIS is your point" with much better accuracy than using just 4 satellites. So that's what receivers do. And then the error detection by space and ground stations being broadcasted to receivers (used only by advanced receivers like SOME aviation GPS systems) so they can correct for those errors makes the precision even one or 2 orders of magnitude better. A GPS-guided missile can literally go to a specific window of a specific building, if you know the coordinates of that window with enough precision. And that's actually the Achilles's heel of the system. It can be used for good or evil. Imagine an ideal John Lennon's world with no evil, then we would not need 4 satellite systems (USA, EU, Russia and China), we could pout all the resources into making only one system much better, and we could make the full accuracy free to everybody, and not be worried about the US (or another actor) "turning it off" in times of war, or with Russia jamming it in times of war. So we cannot relay ONLY in GPS for critical things.
The problem for gnss to be a synthetic ils is jamming and spoofing
Our VOR trained ancestors staring down at us looking at a line on a computer screen.
Gee , I thought that the GPS WAS a little lady in the phone . You spoilt my vision , the lady in my Gps isn't that accurate, I always go on guided tour , because I don't have a tape measure that goes 500 meters. So how does it work . With a plane, please turn left at the big fluffy cloud, 😅😂 stuff it !! The wind blew and the cloud isn't that fluffy , ok so we're going via world tour , to America . Buckle up we're in for a long ride .
Now work out how much petrol you will need .
😂😂
So fog horns work, because the earth is flat. So there it is, the Captain said it.
/s of course.
Sound also travels (in general) in 3 dimensions.
But in the local environment, where the sound can be picked up, it can be assumed that the change of elevation due to curvature of Earth is not that significant.
Can someone please explain: Joe still only has 3 stripes, that means he is no captain right?? How long does it take to become a captain, feel like Joe has enough experience.
Command depends on seniority more than experience. Plus the approx timeframe for someone to become an airline captain differs from place to place. Could be as low as 3 years, could be as much as 10+ years.
When there was no GPS, how a pilot knew the destination position? Moreover, during world war II, pilots I am sure flew the propeller planes without GPS. Thus, how did they know the destination position?
Before GPS you had ground navigation aids. And before that you had a dedicated navigator whose task was to know where you are using stars and other references.
Why was MH370 missing then? They didn’t use GPS? Why was it hard to determine its actual flight path?
Why isn't Galileo mentioned? Or asked differently, why europeans arent pushing for navigation with Galileo since they wanted their own GPS system that would be independent of the U.S.'?
Galileo Is mentioned as one gnss systems at beginning of video... Then you can just refer to generic GPS for it's work and that is valid for Galileo as well
Both Galileo and GLONASS have seen multi-day outages in the past few years. Did anyone notice?
I am not so sure if gps should be the future for precision approaches. Recently interference with gps signals (jamming and spoofing) has sharply increased. Also the war in Ukraine shows these shortcomings as EW (electronic warfare) renders gps pretty much useless. Russian ew in Königsberg/ kaliningrad poses risks and problems to civil aviation in a larger area in Europe.
You missed indias NAVIC system.
Probably because it is regional and not global.
@@NoHandleToSpeakOf not sure of that but I read somewhere that upto Mauritius there is a reach. But still he said list of navigation system. It is not like who is using it.
Video okay but not a big fan