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Global Positioning System: Difference between revisions
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The effects of the ionosphere are generally slow-moving, and can be averaged over time. The effects for any particular geographical area can be easily calculated by comparing the GPS-measured position to a known surveyed location. This correction is also valid for other receivers in the same general location. Several systems send this information over radio or other links to allow L1 only receivers to make ionospheric corrections. The ionospheric data are transmitted via satellite in [[Satellite Based Augmentation System]]s such as [[WAAS]], which transmits it on the GPS frequency using a special pseudo-random number (PRN), so only one antenna and receiver are required. | The effects of the ionosphere are generally slow-moving, and can be averaged over time. The effects for any particular geographical area can be easily calculated by comparing the GPS-measured position to a known surveyed location. This correction is also valid for other receivers in the same general location. Several systems send this information over radio or other links to allow L1 only receivers to make ionospheric corrections. The ionospheric data are transmitted via satellite in [[Satellite Based Augmentation System]]s such as [[WAAS]], which transmits it on the GPS frequency using a special pseudo-random number (PRN), so only one antenna and receiver are required. | ||
Humidity also causes a variable delay, resulting in errors similar to ionospheric delay, but occurring in the [[troposphere]]. This effect is much more localized, and changes more quickly than the ionospheric effects, making precise compensation for humidity more difficult. Altitude also causes a variable delay, as the signal passes through less atmosphere at higher elevations. Since the GPS receiver measures altitude directly, this is a much simpler correction to apply. | |||
==== Multipath effects ==== | ==== Multipath effects ==== | ||
