With the help of a second receiver and

transmitter, it is possible to have

a precision in the range of centimeters.

http://www.popsci.com/technology/article/2013-08/global-positioning-down-inches

https://www.kickstarter.com/projects/swiftnav/piksi-the-rtk-gps-receiver

Other:

http://researchnews.osu.edu/archive/gps3d.htm

http://nextbigfuture.com/2015/05/new-inexpensive-centimeter-accurate-gps.html

http://spectrum.ieee.org/aerospace/satellites/japans-plan-for-centimeterresolution-gps

http://nextbigfuture.com/2014/04/japan-will-boost-gps-accuracy-to-about.html

http://spectrum.ieee.org/tech-talk/transportation/self-driving/cheap-centimeterprecision-gps-for-cars-and-drones

http://www.popsci.com/new-gps-means-hyper-accurate-virtual-worlds

https://www.newscientist.com/article/mg22229694.000-quantum-positioning-system-steps-in-when-gps-fails

http://nextbigfuture.com/2015/04/beyond-gsp-with-atomic-gyroscopes-light.html

http://www.popsci.com/technology/article/2011-08/ground-based-analog-gps-could-make-positioning-technology-accurate-inches

Regards,

Joachim

The issue of resolution in GPS or any Navigation system is dependent on may factors. The GPS satellites transmit the time coded PRN signals which are used by the GPS Receivers to determine the position.

The process is quite complex, but in short one needs to know the exact position of the GPS satellites, the precise time in which the signals are transmitted from the satellites and the distance the signals traverse from the satellite to the receiver often termed as pseudorange for each satellite.

Now, there are certain contributing factors for the errors. One in the stability of the atomic clocks on board the satellite which are constantly monitored by the Ground Control Segment and the ephemeris errors which are obtained by ranging by control segment.

Then a major contribution of error is the Ionosphere, which increases the signal path and very tough to model by single frequency receivers especially for Indian region. The troposphere also adds to the errors. Then there is the contribution of multipath and receiver noise. The Geometric Dilution of precision (GDOP) which is related to the geometry the receiver forms with the satellite also plays a vital role in arriving at the resolution.

The clock correction, ephemeris related correction even iono correction parameters (Klobuchar coefficients) and intimated to the receivers using the Navigation message.

Hence, the accuracy of the system is dependent on Satellites, Receivers and the Ground Control segment along with the algorithms used. The better the models can predict the errors the more efficiently it can be corrected. However, as told we can get very high level of accuracy using SBAS (Satellite Based Augmentation System), Dual Frequency Receivers and using Carrier Phase Measurement Techniques.

Resolution in Navigation is quite an involved subject. Hope it helps. All the best for your research.

Dear Dr Sarkar,

Does rain do the dispersion and hence delay the carrier ?

AR Reddy

Dear Dr Reddy,

                         The effect of Rain in very less in lower bands, it mainly affects signal at higher bands and that also in absorption. So effect of rain in delaying signals may not be a major issue.

Regards.

Mohanchur Sarkar

Dear Reddy:

As is well known an by the standards of today, the resolution or accuracy of handheld GPS is +/- 3 meters. As  Joachim said, in surveying engineering this accuracy can reach few centimeters by differential measurement in a static or real time.

Another way to improve the accuracy for navigation purposes is to combine your GPS with a digital map and match the GPS track to an existing map (assuming the map is more accurate than the GPS coordinates) and use Kalman filter or the like to update your position from the map and the GPS signal.

Regards,

Gamal

Depends on the accuracy of GPS receiver . With the help of different available techniques and solutions, it is possible to achieve the accuracy in centimeters.

Regards

AR Reddy: Just to add to Mohanchur Sarkar's point, liquid water, as well as water vapour, is not dispersive in the L-Band (dispersion is well below 0.05% between the two GPS frequencies). As Mohanchur Sarkar mentioned, liquid water isn't particularly opaque at L-Band frequencies and will only really interact with signals starting at around 15Ghz. I've attached a plot of the opacity of liquid water for three situations: Heavy Rain (Red,yellow,brown, corresponding to different temperatures), light rain (green, turquoise, purple), and snow (Blue). Water vapour, rather than liquid water, is a much more important player at the lower end of the microwave band.

As example of high accuracy GPS (using phase differential mode), it is possible to measure the vertical oscillation of a walking individual wearing a GPS antenna on his/her head:

Terrier, P., & Schutz, Y. (2005). How useful is satellite positioning system (GPS) to track gait parameters? A review. Journal of NeuroEngineering and Rehabilitation, 2(1), 28.

http://www.jneuroengrehab.com/content/2/1/28/figure/F3

Some papers on the accuracy of receivers in forested conditions can be found here..

http://warnell.forestry.uga.edu/warnell/bettinger/GPS/UGA_GPS.html