Determination of horizontal gradients of ionization over Argentina with differential Doppler measurements

Abstract

Differential Doppler measurements of signals from US-Navy Navigational System (NNSS) satellites can be used to obtain the electron content of the ionosphere. Measurements carried out using data from four stations on Argentine. Differential Doppler data from two stations are combined, resulting in considerably more reliable results, particularly when there is strong horizontal structure in the ionosphere, as is often the case in the Equatorial and polar regions. Range difference measurements are influenced by differences of electron content or “horizontal gradients”, and the role of gradients is demostrated. Unfortunately, the presently available ionospheric models give no realistic indication of horizontal gradients and therefore we have to rely on experience from measurements and one's estimates from atmospheric / ionospheric physics. The availability of observed data is discussed together with the relevance of conclusions from measurements and estimates.