Atmospheric Errors on GPS Range Boundary between iono GPS stellite orbit Geometrie distanee troposphere Center of mass of the earth av Principles of the Global Positioning System 005-4-1(9) GPS Major Error Sources Propagation media ionosphere(50-1000km) the presence of free electrons in the geomagnetic field causes a nonlinear dispersion of electromagnetic waves traveling through the ionized medium group delay (code range is measured too long)and phase advance(phase range is measured too short), frequency dependent; can reach -150 m near n=1-3+. group refractive index(group of waves, such as code GPS signal) nm=1+-+.. phase refractive index constant C,=-403N [H=]thus n >n since electron density N is always positive PRIncples of the Global Positioning System 20054-1(105 Principles of the Global Positioning System 2005-4-1 9 troposphere ionosphere Geometric distance Actual signal path Boundary between iono and troposphere Atmospheric Errors on GPS Range Principles of the Global Positioning System 2005-4-1 10 • Propagation media • ionosphere (50-1000km) • the presence of free electrons in the geomagnetic field causes a nonlinear dispersion of electromagnetic waves traveling through the ionized medium • group delay (code range is measured too long) and phase advance (phase range is measured too short) , frequency dependent; can reach ~150 m near the horizon; constant 40.3 [ ] thus since electron density is always positive 1 phase refractive index 1 group refractive index (group of waves,such as code GPS signal) 2 2 2 2 2 2 e gr ph e ph gr c N Hz n n N f c n f c n = − > = + + = − + … … GPS Major Error Sources