GPS Receiver Ionosphere Error Correction Based on Spatial Gradients and IGS Satellite DCBs

摘要

This paper presents a spatial gradient based approach to estimate ionosphere TEC for dual frequency receivers. A conventional dual frequency receiver calculates the ionosphere error by differencing the L1 and L2 pseudorange measurements. The results are contaminated by the difference in the two signals propagation time through the satellite transmission system and the receiver, known as satellite and receiver differential code bias (DCB) respectively. While satellite DCBs are relatively stable and can be monitored and calibrated by various GNSS monitoring networks, the receiver DCB is dependent on the receiver environment, antenna and circuit design, and receiver signal processing algorithms and is difficult to calibrate or model. This paper treats the ionosphere slant TECs and the receiver DCB as unknowns in the range equations. Each slant TEC is related to the vertical TEC at the corresponding receiver-satellite ionosphere piece point (IPP) through the mapping function. We model the vertical TEC at an IPP as having contributions from the receiver zenith vertical TEC and from the TEC spatial gradients. By utilizing the satellite DCB values made available through the Global Ionosphere Map (GIM), the zenith vertical TEC, the TEC spatial gradients, and the receiver DCB can be solved simultaneously from carrier smoothed pseudorange difference equations. The paper presents the vertical TEC, TEC gradients, and receiver DCB for two receivers located in a mid-latitude and a low-latitude location and compares the results with that of the TEC map provided by GIM.