# Questions tagged [gps]

The Global Positioning System is a global satellite navigation system created and maintained by the United States. The Galileo project is a European Union global satellite navigation system serving the same role.

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### Do satellites in orbit create Relativity paradoxes? [closed]

Can someone point out the flaw in this very realistic scenario below? I will start by stating established first principles of the applicable orbital and relativistic conditions. Then I will describe ...
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### Where special and general relativity must be used in engineering?

As I know Newton physics is used for most engineering, aerospace, mechanical, naval etc. Where we must use Theory of Special Relativity and Theory of General Relativity to get correct results, only ...
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### Is it possible for 4 satellites cannot render a position fix on Earth?

I recently learnt about how GPS works and how it uses the intersection of spheres to locate a person which got me thinking whether 4 spheres can always guarantee a position fix. My understanding is ...
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### The muometric positioning system, how does it work exactly?

While GPS uses light signals to determine the location of a device, I just learned that something similar can be done using cosmic muons rather than light, see e.g. this paper. The idea, as I ...
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### Why is the Accuracy in the measurement of Time so important in GPS?

I read in a physics book that Without clocks of extreme accuracy, the Global Positioning System (GPS) that is now vital to worldwide navigation would be useless. What would be effects on navigation ...
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### How to calculate accuracy of a calculated (predicted) coordinate (latitude, longitude)?

Given GPS data that consists of: Latitude Longitude Bearing (degrees) Speed (meters per second) Accuracy (radius of the circle around the coordinate where true position can be found with 68% chance, ...
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### GPS clocks and special relativity effects [duplicate]

I've got question about global navigation systems. In internet sources i found that atomic clocks in satellites will slow down for 7us per day because of special relativity effects and speed up for ...
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### Why don't we put satellites into an orbit where there is (almost) no time dilation/contraction compared to Earth's surface?

Consider: On this image, if I understand correctly, the time dilation diagram is shown depending on the height for circular orbits. First in low orbit, time slows down relative to the surface due to ...
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### "Earth spinning faster will break GPS and atomic clocks".. Umm, how?

Since it's just come out that Earth is apparently spinning about a milliscecond and a half faster.. I see a bunch of "articles" claiming this will.. somehow.. break atomic clocks and make ...
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### Would obliquity and precessional changes of Earth affect the accuracy of GPS-based measurement of tectonic movements?

The rate and direction of tectonic movements can be measured by comparing the coordinates of the same GPS receiver over time. The coordinates are obtained using trilateration. All materials I could ...
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### Determining Feet Above Sea Level with IPhone

I found a site on my IPhone that calculates how many feet above sea level my house is. Initially, it indicated 986 feet above sea level, but then the amount of feet began to fluctuate. Is this ...
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### Distance between two points on Earth (arc length) doesn't increase with altitude (radius) according to GPS

Consider the following example: Point A has coordinates 45 lat, 0 long. Point B has coordinates 45 lat, 2 long. Both points are 5000 ft above sea level. The distance between them is X. Point C has ...
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### Explaining the phrase "as viewed by A, clock $\mathfrak B$ appears to be ticking faster than clock $\mathfrak C$"

In writings concerning time dilation and GPS (incl. on PSE) one can find statements such as When viewed from the surface of the Earth, the clocks on the satellites appear to be ticking faster than ...
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### What are the real-life applications of General Relativity? [closed]

As we all know, the most famous application of GR and SR is the GPS guidance system, where time dilation can be corrected. But it seemed that everywhere I go, GPS is the only answer to how GR can be ...
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### Does special relativity's kinematic time dilation have a physical effect on matter, and how can you test this? [duplicate]

Kinematic time dilation or else named constant velocity time dilation is an apparent time dilation effect but with real consequences on how we measure time and our everyday life like the GPS ...
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### How was the first atomic clock calibrated?

As we all know, atomic clocks are being used to measure time and the GPS system. But I was wondering based on what was the first atomic clock calibrated and how accurate this calibration was based on ...
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### How robust is the international atomic time standard against malicious actors?

This answer explains the international atomic time standard (TAI). The fact that the Russian GLONASS and American GPS systems are referenced to their national clock systems, which are then ultimately ...
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### Why is not the $g$-field of the sun considered in the GPS-settings?

I have read this SE-Physics question and its answers, however, I could not find anything regarding the effect of Sun's $g$-field on the GPS clocks. When a GPS clock orbits earth, depending on whether ...
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### How does the GPS time signal achieve an accuracy of <= 40ns relative to UTC?

From the official GPS website: How accurate is GPS for timing? GPS time transfer is a common method for synchronizing clocks and networks to Coordinated Universal Time (UTC). The government ...
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### Accelerometer vs linear acceleration during an impact

I am trying to understand the relation between the accelerometer and linear acceleration during impacts. At work we have an accelerometer and gps onboard sensors installed in a few cars. The ...
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### Atoms with energy differences corresponding to wavelengths 19.05 cm, 24.45 cm and 25.48 cm

I was just wondering whether there are any known atomic transitions in Oxygen, Nitrogen, Hydrogen or Helium atoms/ions which emits wavelengths in any of the regions: 19.05 cm, 24.45 cm and 25.48 cm. ...
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### Time dilation in satellites [duplicate]

Is the time dilation suffered by clocks in GPS satellites accurate to what is predicted by special relativity? By "accurate" I mean to ask if the numerical answer given by relativity equations match ...
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### Time dilation in general and in particular for two opposite GPS satellites

I am going throw reading on relativity and youtube explanations at the moment. So far, I got next understanding and some questions: There is time-space thing. Moving through space at the speed of ...
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### Calculate acceleration and lateral G force from GPS coordinates [closed]

I have a data logger that records time (in tenths of seconds), latitude and longitude. I would like to calculate my acceleration and lateral G force based on the collected data. Is someone able to ...
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### Time dilation in a geosynchronous orbit

since gravity slows time, and velocity slows time, would observer A on the equator directly under observer B in a geosynchronous orbit experience time at the same rate? Time would slow on the surface ...
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### Number of GPS satellites required to give 100% coverage

I am a Belgian school student in sixth grade of secondary school (the Belgian equivalent of High school). Together with two class mates we were assigned to write some kind of essay about the Global ...
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### Estimating a new latitude/longitude using 2 previous datapoints and elapsed time: proofcheck help

I'm doing this all in code, could anyone with a better understanding of physics than mine read over my method to make sure my principle is sound? I have a device constantly sending a timestamp and it'...
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### Why isn't the GPS location calculated from the Schwarzschild metric?

The GPS uses the flat space light propagation formula to calculate the distance from the source (the satellite) to the receiver (observer on Earth): $$d=c \cdot \Delta t$$ where $c$ is the speed of ...
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### Would Earth clocks tick faster than a clock on a GPS satellite if we disregard gravitational time dilation?

If we disregard the time dilation caused by a GPS satellite being in lower gravity, would earth's clocks tick faster or slower from the satellite's perspective? Edit. From earth, we understand that a ...
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### How do I calculate time dilation on GPS satelites due to Earth's mass?

I found this answer which gives as the formula $$T_2 = \frac{T_0}{\sqrt{1-\frac{2GM}{c^2 R}}}$$ that should result in the time $T_2$ passed on a GPS satellite while $T_0$ seconds pass in the center ...
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### Electromagnetic Waves and GPS

If the global positioning system functions through radio waves, but radio waves are reflected in the ionosphere, then how do these electromagnetic waves reach the satellites?
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### Why do GPS satellites care about Earth clock at all? (relativity)

Many online resources make grandiose claims about how GPS would be useless without relativistic corrections. Specifically, they outline that satellite clocks runs slower by 7μs/day due to special ...
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### How are GPS corrected for special/general relativity?

I was looking for the equations that are used by the GPS receiver to calculate its position and time correction (bias). By looking at the Navigation Equations on Wikipedia, I don't see any account for ...
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### Would GPS work in a (locally) newtonian universe?

Often, when there are question on why fundamental research makes sense or is neccesary, I've seen answers like "GPS is used everywhere today, and it wouldn't work without relativity". Of course, if ...
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### What is the current limiting factor for GPS clock synchronization precision?

In the (slightly dated) paper 'Quantum Clock Synchronization Based on Shared Prior Entanglement' [R. Jozsa et al., Phys. Rev. Lett. 85, 2010 (2000)], the authors describe the GPS synchronization ...
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### How many caesium clocks are there on each GPS satellite ? Is there any other atomic clock on-board?

I am trying to find how many caesium atomic clocks are carried by each of the GPS satellites. And whether the satellites also carry other atomic clocks, such as rubidium or hydrogen clocks.
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### If relativity is symmetric, do the satellites in the GPS system see the earthbound clocks as running slow due to relativistic time dilation?

If relativity is symmetric, do the satellites in the GPS system see the earthbound clocks as running slow due to relativistic time dilation? How much slower does the satellite see the earthbound ...
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### Can GPS signals penetrate steel in the thickness of few centimeters?

Can GPS signals penetrate steel in the thickness of few centimeters? Can they penetrate even thicker steel or other materials than steel (as well as steel?)?
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### How are three satellites sufficient to find a unique point in GPS? What happens in case of an overlap? [closed]

Is it because the 2nd and 3rd satellites' centres are collinear? How is satellite overlapping avoided? If not avoided then what happen to the signal sent from an overlapped satellite?This is just a 2D ...
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### Why GPS signals doesn't work indoors but mobile signal does?

GPS signals 1000-1500MHz range doesn't seem to work indoors (sometimes it does) but cell phone signal 1800/900 MHz works? Can mobile phone signals penetrate solid matter like homes/offices etc?
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### Electromagetic Waves Behavior

In the radio spectrum, higher frequencies attenuate faster. Also, in my understanding, higher frequencies travel more along line of path. Lower frequencies can penetrate through solid materials but ...
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### light-time correction in GNSS service

I have tried to use C/A code for single point positioning with light-time correction. I found the below equation for that.Can any one explain how to use this equation for light-time correction? \...
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### Do relativistic phenomena affect communication with satellites?

Communication with satellites certainly requires knowing the speed of light. Beyond having that magic number, do relativistic phenomena affect communication with satellites? For example, would one ...
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### In what way has GPS had an impact on our understanding of physics?

I've been reading about the effects GPS has had on our society with the February launch of a IIF Satellite and I was wondering if launching GPS satellites and the actual GPS satellites have lead to ...
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### Does barometer improve gps position accuracy?

It is clear that a barometer is more accurate in measuring altitude than GPS. However is it true that the barometer improves GPS position accuracy? Would be a GPS device and a GPS+barometer device ...
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### How does GPS on an airplane report a 100 km error?

On a flight across Europe, I took my iPhone out to see if the GPS can find my position. I was sitting away from a window, so reception would have been bad. I wouldn't have been surprised to get no ...
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### Why would a modern smartphone not work if the theory of general relativity hadn't been discoverd? [closed]

My teacher told me that todays smartphones wouldn't work if the theory of relativity hadn't been discovered, but he didn't explained why.
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### Time Synchronization Between 2 GPS Controlled Rubidium Clocks [closed]

I have 2 GPS Controlled Rubidium Clocks I need it to be synchronized to one another to the level of a microsecond. My question is what is the max phase (ns) allowed from the clock's input 1pps, for ...
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### I don't see that general relativity is really needed for GPS to work correctly [duplicate]

From what I understand, GPS localization is based on the difference in the reception time from the time of emission of a signal from different GPS satellites whose positions are known. For this we ...
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I have a $\text{i2c}$ GPS module I got working yesterday, and here are my co-ordinates. Latitude: 44.901354999999995 Longitude: -68.97112333333333 What I am having trouble figuring out is that ...