Estimation Propagation Delays Induced in GPS Signals by Some Atmospheric Constituents

Abstract

When radio waves propagate through the earth's neutral atmosphere, the radio signals are affected significantly by the variability of its refractive index, which causes primarily in the delay of the arrival, usually referred to as the tropospheric delay. The Global Positioning System (GPS) is space-based radio navigation. The GPS system receiver provides exact location and time information for an unlimited number of users in all weather, day and night, anywhere in the world. The GPS used three frequencies that are (L1 = 1.57542 GHz, L2 = 1.22760 GHz and L3 = 1.38105 GHz). The work part mainly focuses on how to illustrate and model the effects of the atmospheric constituents such as, water vapor, clouds, rain and snow on the GPS frequencies.The differential phase shift (∆∅) in case of rain is caused by the oblate rain drop that is has two different axes, and because of the difference of the concentration of rain drops, also (∆∅) doesn't depend on the temperature but increase with the increase of the frequency where the values of (∆∅) are 6 deg/km for L1, 5 deg/km for L2 and 5.4 deg/km for L3. The differential attenuation (∆A) in case of rain in addition to depend on the shape of rain drop and the concentration of drops, it depends on the temperature and the frequency. The (∆∅) in case of snow caused by the irregular shape of snow particle and depends on the temperatures and the frequency. The (∆A) in case of snow has very low values in different temperatures and frequencies.