Refractometric sounding of the Earth's atmosphere using a multiorbit system of Global Positioning System (GPS) and low-Earth orbit (LEO) satellites is modeled on the basis of data from the model of global atmospheric circulation (ECHAM3). The errors of the tomographic reconstruction of meteorological fields are investigated because of insufficient measured refractometric data. For a system of 100 LEO and 18 GPS satellites the estimates of errors of geopotential and temperature is obtained, which are 3--5 m and 0.3 K, respectively, in the pressure range 10--200 mbar. ¿ American Geophysical Union 1996