Transformation of Neill Mapping Function for GPS Tropospheric Delay

Abstract

The refraction of the Global Positioning System (GPS) signal as it passes through the neutral atmosphere from the satellite to the earth can be referred as GPS tropospheric delay, which causes longer distance traveled by the signal. The tropospheric delay is the product of zenith tropospheric delay and mapping function. Many mapping functions have been established for calculating the tropospheric delay at arbitrary elevation angles. The mapping functions give large value especially for the elevation angles less than 5 degrees. A transformed Neill Mapping Function (NMF) has been proposed to be an alternative mapping function. The result shows a significant reduction of mapping function scale factor. As the coefficient of the zenith tropospheric delay, the value of modified mapping function will directly reduce the total tropospheric delay. The transformed Neill Mapping Function has improved the tropospheric delay up to 17.8 percent for two degrees elevation angles, compared to the Neill Mapping Function.