Associating the measurement methods and considering the relations between the parameters of the equipment and those of the ionosphere, various methods of ionospheric corrections are discussed in this paper. The main conclusions are: (1) The criteria to compare various methods are that the ionospheric parameters must be measured in real time and position as the observation of individual radio source; the time interval during which the ionosp heric parameters are measured must be same as that during which the data to be corrected are me asured. (2) As the radio source is strong ennough, it is reasonable to use the mean feature of the ionsphere during about 10 seconds to mabe ionospheric correction for the ionospheric model method and dual frequencymenop. but for the reference radio point source method, taking Dmax=1 km, the mean feature of the ionosphere during about 3 minuts must be used. (3) When the scale of the irregulaties of the ionosphere is larger than the base line length, the ionospheric influence can be eliminated effectively by utilizing the reference radio point source method, as the reverse condition is true, closure phase technique is more desirable. (4) If dual frequency observation is applied, the dual frequency method is the most reasonable one to eliminate the influence of the ionosphere.
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