Topex dual frequency altimeter studies : ionospheric corrections and ocean surface measurements
thesisposted on 15.12.2014, 10:40 by Jonathan Price. Angell
The TOPEX/Poseidon altimetry mission was developed as a NASA/CNES collaboration to provide accurate sea surface height (SSH) measurements. The TOPEX mission's altimeter is the first, and so far only, dual frequency system in space. The use of two frequencies allows a correction to be made for the radar pulse delay imposed by the Earth's ionosphere which would otherwise lead to an underestimation of SSH. Not only does TOPEX/Poseidon provide the most accurate SSH measurements yet from space, it also provides the first ever quasi-global measure of the integrated electron content (IEC) of the ionosphere. This thesis utilises TOPEX/Poseidon data in a combined study of both the oceans and the ionosphere.;Firstly a study of the dependence of the IEC on geomagnetic disturbances, and the spatial coherence scale of the IEC is performed by comparison with the International Reference Ionosphere, an empirical ionospheric model. A systematic dependence of IEC with geomagnetic disturbance is found, and the first ever quasi-global maps of IEC spatial coherence distance are produced. This investigation may lead to an improvement in the accuracy of the model, and hence also that of single frequency altimeter systems, which must rely on such empirical models for their correction to the ionospheric delay.;Secondly the tropical Pacific Ocean is studied, in particular the characteristics of large scale wave activity in relation to the devastating climatic/oceanic phenomena known as El Nino. Kelvin, Rossby and tropical instability waves are identified, and their interactions and possible mechanisms related to El Nino are investigated. Evidence for both western and eastern boundary reflections are presented, and their significance to the delayed oscillator mechanism is discussed. The study illustrates the necessity for highly accurate SSH measurements.