We have refined values of critical frequencies, obtained from the IRI model, for a given hour at certain space points adjacent to the site for which vertical ionospheric sounding data are available. The refinement is based on data on the difference between ionospheric delays of signals received from two navigation satellites at one point in time. As reference values we have used the differences calculated from the ionospheric total electron content, obtained from IONEX maps. As derived from data for 20 pairs of satellites, the mean value of the relative difference between the refined critical frequency and the estimated one is 9.8 %.
Critical frequencies specified by the IRI model are determined for a given hour at two closely adjacent space points. A correction parameter is differences between pseudo-distances of signals from a pair of navigation satellites, recorded by a single-frequency receiver. We compare the differences calculated from measurements of the total electron content at frequency correction points and from the model with fitting of critical frequencies at these points. It is shown that in most cases the similarity between model and experimental values of the pseudo-distances difference exists when critical frequency variations do not exceed 30%.
We develop an approach that uses simultaneous measurements of pseudo-distances from two GNSS navigation satellites made with a single-frequency receiver for an hour period to perform local correction of an ionospheric background model for current situation. Within the analytical component of a single-layer ionospheric model, we conduct a comparative analysis of the degree of influence of variations in the basic parameters of vertical electron density profile on pseudo-distance variations. We have established that critical frequency variations make the most significant contribution. Also important, however, is the consideration of electron density variations at heights well above the maximum. We present principles of the proposed correction method.
This report describes a method for estimating ionospheric signal delay for pseudorange GNSS measurements made with a single-frequency receiver. To reduce the influence of the instability of the time scale of the receiver, we determine the difference between magnitudes of ionospheric delay of signals from two satellites at one time. To eliminate random fluctuations from the difference, we average data over a period from 30 to 60 minutes. Numerical simulation is carried out to determine the influence of a change in the critical frequency and height of the ionospheric maximum on pseudorange. It is shown that under favorable conditions variations in the ionospheric delay difference can be used to correct the ionospheric model that reflects hourly variations in its parameters. We study a method for determining current values of critical frequencies of the ionosphere for a regional correction of its model.
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