Differential and Precise Point Positioning in the South American Region with lonosphere Maps

This paper presents two strategies for improving GPS coordinate solutions using regional ionosphere maps in South America, a region susceptible to strong ionospheric activity.Since 2005, the La Plata Ionospheric Model (LPIM) has been used to routinely generate Vertical Total Electron Content (VTEC) maps at the La Plata Processing Center (CPLAT) using about 50 GPS stations in South America. VTEC is modelled using a linear combination of undifferenced GPS carrier phase observations in modified dip latitude or modip: tan μ = I/√ cos φWhere √ is moddip latitude, I the magnetic dip and φ the geographic latitude. A particular approach is used to solve the hardware related biases.Since 2003, the Instituto Brasileiro de Geografia e Estatistica (IBGE) has collaborated in order to maintain the SIRGAS Reference Frame in South America, delivering weekly coordinate solutions using the same set of permanent stations that the CPLAT uses for computing ionosphere maps.This work examines two possible benefits of VTEC maps in GPS processing, namely, solving ambiguities in differential solutions and mitigating ionospheric biases in undifferenced single-frequency solutions.In differential processing, ionosphere maps are applied in the ambiguity resolution step when using the Bernese GPS processing software. For undifference processing, ionosphere maps are input to mitigate ionospheric biases when using the Precise Point Positioning (PPP) software developed by the Geodetic Survey Division (GSD), Natural Resources Canada (NRCan).In order to validate the authors’ proposal, data from four different periods in 2006 from a network of GPS stations near the ionospheric anomaly region in the South Atlantic and equatorial regions were tested with and without VTEC regional ionosphere maps.