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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