GPS Major Error Sources Troposphere(up to 50 km)-frequency-independent, same for all frequencies below 15 GHz(troposphere is not dispersive for frequencies below 15 GHz) group and phase delay are the same elimination by dual frequency is not possible affects relative and point positioning empirical models(functions of temperature, pressure and relative humidity) are used to eliminate major part of the effect differential effect is usually estimated(neglected for the short baselines with similar atmospheric effects) total effect in the zenith direction reaches 2.5. and increases with the cosecant of the elevation angle up to 20-28 m at 5deg elevation ey Principles of the Global Positioning System Tropospheric Effects(cont The tropospheric propagation effect is usually represented as a function of temperature, pressure and relative humidity Obtained by integration of the refractivity Ntrop △ 10° Nods where integration is performed along the geometric path It is separated into two components: dry(0-40 km) and wet(0-1lkm) △m=△,+△ trop Represents an example of refractivity model at the surface of the earth cl, c2, c3 are constants, Tis temperature in Kelvin(K), e is partial pressure of water vapor [ mb], p is atmospheric pressure mb] Principles of the Global Positioning System 200541(168 Principles of the Global Positioning System 2005-4-1 15 GPS Major Error Sources ¾ Troposphere (up to 50 km) - frequency-independent, same for all frequencies below 15 GHz (troposphere is not dispersive for frequencies below 15 GHz ) ¾ group and phase delay are the same ¾ elimination by dual frequency is not possible ¾ affects relative and point positioning ¾ empirical models (functions of temperature, pressure and relative humidity) are used to eliminate major part of the effect ¾ differential effect is usually estimated (neglected for the short baselines with similar atmospheric effects) ¾ total effect in the zenith direction reaches 2.5, and increases with the cosecant of the elevation angle up to 20-28 m at 5deg elevation Principles of the Global Positioning System 2005-4-1 16 ∫ − ∆ = 10 6 N ds trop trop d w trop ∆ = ∆ + ∆ 0 1 2 3 2 T e c T e c T p N c trop = + + Tropospheric Effects (cont.) ¾ The tropospheric propagation effect is usually represented as a function of temperature, pressure and relative humidity ¾ Obtained by integration of the refractivity Ntrop ¾ where integration is performed along the geometric path ¾ It is separated into two components: dry (0-40 km) and wet (0-11km) ¾ Represents an example of refractivity model at the surface of the earth; c1, c2, c3 are constants, T is temperature in Kelvin (K), e is partial pressure of water vapor [mb], p is atmospheric pressure [mb]