Magnetic fields measured by sratospheric balloon flights and their role for the poblem of constructing an analytical model of the magnetic field of the Earth's crust

The development of satellite geomagnetic surveys enables to elaborate a joined model of magnetic anomalies for the near-Earth space and at the Earth's surface. The Earth's magnetic field and its vertical gradients at altitudes of 20-40 kin are a form of connecting link for satellite and aeromagnetic surveys. They allow studying the spatial distribution of magnetic anomalies and their structure in the near-Earth space. These spatial properties are of special importance when models for the structure of the Earth's crust are studied. According to [1] from the mathematics of modeling the internal magnetic field there results that the different physical properties of magnetic field data in dependence on the altitudes cause that only a mean field model is derived when field data from different altitudes are commonly used without any reasonable continuation procedure. Consequently, the ill-posed problems of upward and downward field continuations must be approximated in an appropriate way by considering e.g. recorded field data at different altitudes in order to improve the field modeling. This problem is of special importance when small field constituents as the crustal contributions are studied. The data of the magnetic field and its vertical gradients at altitudes of 20- 40 kin are used for this goal. Measurements are carried out by the balloon magnetic gradiometers with a measurement base length of 6 km oriented along the vertical line. The results enable to perform high-precision magnetic surveys and to extract qualitatively magnetic anomalies along extended routes of surveys. This method allows to obtain excellent data of the interior terrestrial magnetic field in zones of aurorals and of equatorial electrojets as well as in polar cap regions. In polar regions the anomalous magnetic fields obtained in this way are indispensable for constructing a global field model for the magnetic anomalies.