The application of GPS in monitoring the ionosphere is also the beginning of GPS space meteorology. Space is full of plasma, cosmic ray particles, and electromagnetic radiation of various bands. Because the sun often throws out millions of tons of charged objects in one second, the ionosphere is strongly disturbed. This is space weather. an object of research. The total free electron content (TEC) per unit volume is determined by measuring the delay of the ionosphere to GPS signals to establish a global digital model of the ionosphere.

　　GPS satellites transmit L1 and L2. two carriers. By these two carriers, the influence of the ionosphere on GPS positioning can be weakened, or the ionosphere refraction can be determined. Because this refraction is related to the carrier frequency.

　　When one builds a regional or global numerical model of the ionosphere, the simplifying assumption is always made that all free electron content is represented on a single plane, which is H above the ground. In this way, the electron content can be expressed as the electron content Es at the intersection point (piercing point) between the receiver and satellite line and the single layer, which can be regarded as the function Ecos of E and the zenith distance Z' at the penetration point Z'=Es. The electron concentration Es on the spherical surface can be modeled, for example, it is written as a spherical harmonic function of latitude and longitude, and many experts have proposed various models in this regard. IGS proposes an ionosphere map exchange format (10nosphere Map Exchange Format, IONEX-Format), its function is to make ionosphere maps obtained based on various theories and technologies to be integrated and compared on the basis of unified specifications . The ionospheric models have different theoretical foundations, and the technology of the data sources obtained is also different, and the data coverage is not complete. Therefore, at present, only the differential code deviations (differential code deviations) of the IGS and various TEC maps around the world and GPS satellite signals can be obtained. code biases—DCBS) are provided to users all over the world in the form of IONEX, and the next step will be to gradually combine them through comparison.

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