Differential corrections in GLONASS and GPS navigation.

     One of the way of improvement of location accuracy with use of satellite navigation systems (GPS, GLONASS) are differential corrections (1). A principle is not new, in navigation saved up error in points with known co-ordinates traditionally writes off. Actually differential corrections have started to apply in landbased navigating systems (2). The idea is simple enough - in a place with precisely known co-ordinates antenna of the navigating receiver is installed and the difference of the true and measured values which is in a greater degree a regular error (3), transferred to the consumer. It would seem, all is simple - to transfer a difference of co-ordinates. But, there are some nuances. Let's remeber a principle of definition of co-ordinates and the major sources of errors.

      Measured parametres of the receiver are pseudoranges (4) from the antenna of the receiver to the satellites, defined on a radio signal delay. Co-ordinates of the receiver antena are calculated on co-ordinates of four and more satellites at the moment of signal output and on  previously measured pseudoranges. Accurate co-ordinates of satellites are calculated on ephemerides (5), transferred by satellites.

     From this it is possible to estimate what influences a positioning error.

     First, certainly, conditions of radio-waves transmission. To a wave, making the way from a free space to the Earth, it is necessary to pass through different atmospheric layers where it refracts.