Application of radio holographic method for observation of altitude variations of the electron density in the mesosphere/lower thermosphere using GPS/MET radio occultation data

Abstract

A radio holographic method for observation of wave phenomena in the upper atmosphere (height interval 60– 120 km ) is described. The radio holography uses coherent properties of the rays propagating through the atmosphere. These properties arise due to the high stability of the GPS signal and its high sensitivity to layered structures in the atmosphere and ionosphere. High angular and vertical resolution of the radio holographic method has been revealed with the use GPS/MET radio occultation data. Multibeam propagation in the troposphere and weak reflections from the ocean surface have been observed with vertical resolution better than 70 m . Radio holographic method gives the possibility to remove the contributions of the upper layers and to identify detailed structures in the electron density altitude profiles in the D- and E-layer of the ionosphere. The main effects connected with the influence of the D- and E-layer on the phase path are correspondingly of the order of 0.5–2 and 10– 30 cm . The instrumental accuracy of the GPS phase path measurements was of the order of 1– 2 mm . The fine structures in the D-layer and the sporadic E-layer have been inferred. They have a vertical spatial period of 1– 2 km, changes in the electron density vertical gradient from ±0.5×10 3 to ±10×10 3 electrons/( cm 3 km) and the electron density variations from 100 el/ cm 3 to 1000 el/ cm 3 . Electron density altitude distribution and its gradient with maximum values ∼45×10 3 el/ cm 3 and ∼20×10 3 electrons/( cm 3 km), respectively, have been observed in an E-layer of the ionosphere at the height interval 92– 100 km . The possibility of a qualitative measurement of the vertical distribution of the horizontal wind velocity in the E-layer region using GPS/MET radio occultation data is considered.