Solutions Of Inaccuracy In Gps

Electronics errors are among various accuracy-degrading effects. They include ionospheric effect, ephemeris effects, satellite time errors, multi-path shift, tropospheric effect, and numeric errors.

Inconsistencies of weather conditions affect the speed of the GPS signals as they pass across the Earth’s atmosphere and ionosphere. Fixing these errors is a considerable challenge to improving GPS position accuracy.

These errors are smallest when the satellite is directly overhead and become bigger for satellites closer to the horizon because the signal is affected for a longer time. As soon as the receiver’s approximate location is identified, a mathematical model could be applied to estimate and correct for these errors.

Since ionospheric delay affects the speed of microwave signals in a different manner based on frequency – a characteristic called dispersion – both frequency bands could be employed to assist in reducing this error. A few military and costly survey-grade civilian receivers compare the different delay in the frequencies to assess atmosphere dispersion and apply a more accurate correction.

This could be done in civilian GPS receivers without deciphering the P(Y) signal carried on L2 by tracking the carrier wave rather than the modulated code. To achieve this on lower cost receivers, a new civilian code signal on L2 known as L2C was added to the satellites. This new signal allows for a direct comparison of the L1 and L2 signals using the ciphered signal rather than the carrier wave.

The effects of the ionosphere usually change slowly and could be averaged over time. The effects for any specific geographical region could be easily calculated by comparing the GPS-measured location to a known surveyed location. This rectification is also valid for other receivers in the same general position.

A lot of systems send these information over radio or other links to allow L1 only receivers to make corrections. The date is transmitted through satellite system and transmits it on the GPS frequency using a special pseudo-random number so only a single antenna and receiver is necessary.

In addition, Humidity causes a variable delay resulting in errors like the ionospheric delay but occurring in the troposphere. This effect is localized to a greater extent and alters more rapidly than ionospheric effects and is not frequency dependent. These characters make it a great deal more difficult to make accurate measurement and compensation for humidity errors than with the ionospheric effects.

Shifts in altitude likewise change the amount of delay because of the signal passing across less of the atmosphere at higher elevations. Since the GPS receiver calculates its approximate altitude, this error is comparatively simple to correct.

GPS signals could also be affected by multi-path issues where the radio signals reflect off of surrounding terrain like buildings and hard ground. These delayed signals could cause inaccuracy as well.