Neutral Atmospheric Delay Effects on GPS C/A Code for Precise Navigation Applications

The Global Positioning System (GPS) is a satellite-based navigation system that provides a precise three-dimensional user position (x, y, z), velocity and time. Electromagnetic carrier signals transmitted by each satellite are affected by the transmission medium, i.e., earth's atmospheric layer in particular the nonionized tropospheric layer. For many precision applications, position estimates need to be corrected for number of errors, and one of the major error sources to be corrected is satellite clock error and propagation path delay in the troposphere, which is lower atmospheric layer, also known as neutral atmospheric layer (extending from the earth's surface up to an altitude of approximately 50 km). The problem in determining the tropospheric delay is the modeling the wet delay components with high precision, as these components (temperature, humidity and pressure) of the neutral atmospheric layer are highly influenced by the distribution of water vapor which cannot be precisely predicted. These atmospheric parameters act as additional unknowns in the analysis of GPS data and in estimation of receiver position. The tropospheric delay at zenith is about 2 to 4 m. In this paper, the tropospheric delay estimation method proposed is function of orbital dynamics and atmospheric conditions. The pseudorange computed using the C/A code measurements of carrier signal transmitted by each satellite is corrected for this delay and aging of atomic clock and compared with the geometric range. The delays are estimated for the typical data collected on March 11, 2011 from the dual frequency GPS receiver located at Department of Electronics and Communication, Andhra University College of Engineering, Visakhapatnam.