GPS amplitude radio holography: Application to remote sensing of the atmospheric and ionospheric processes

Since 1995, the global positioning system (GPS) has been exploited for remote sensing in the radio occultation (RO) scheme to obtain the vertical profiles of refractivity, temperature, pressure and water vapor in the neutral atmosphere and electron density in the ionosphere with global coverage. In the GPS RO scheme the GPS transmitter emits radio signal, which propagates through the ionosphere and the atmosphere, and then arrive at a receiver installed on the Low Earth Orbit (LEO) satellite. The receiver registers the phase and amplitude of the radio waves during the LEO orbital motion and produces two 1D radio holograms at two GPS frequencies f1=1575.42 MHz and f2=1227.6 MHz. The radio holographic approach (RFSA, CT, BP and other methods) can be used to reveal the vertical profiles of the physical parameters in the ionosphere and atmosphere along the trajectory of the motion of the tangent point, where the GPS signal trajectory has a minimal height above the Earth's surface. Applying the GPS RO remote sensing to the Earth's atmosphere study was demonstrated for the first time with the GPS/MET experiment. Since then several satellite missions have been launched with GPS occultation receivers including OERSTED, SUNSAT, CHAMP, SAC-C, and GRACE. Future RO remote sensing investigations that are planned now include ROCSAT3/COSMIC and Terra-SAR missions. This requires modernization of radio holographic methods in the RO remote sensing technology with the goal of heightening the accuracy and broadening the potential of the GPS RO remote sensing method. In this contribution a be new radio holographic amplitude method for GPS RO remote sensing is presented. This method allows one to measure the vertical gradients of the refractivity in the atmosphere and electron density in the lower ionosphere, monitoring the internal waves activity in the atmosphere, studying the ionospheric disturbances on a global scale. As follows new radio holographic method may be informative for investigations of the connections between processes in the atmosphere and mesosphere, analysis of the influence of the space weather phenomena on the lower ionosphere.