The Continuous Wavelet Transform, a Valuable Analysis Tool to Detect Atmospheric and Ionospheric Signatures in GPS Radio Occultation Phase Delay Data

GPS radio occultation phase delay (PD) data contain valuable information about atmosphere and ionosphere and its structure, based on the recorded changes of the direct GPS signal between LEO and GPS satellite. PD data contain signatures of surface reflections mainly above water and snow/ice covered regions which have successfully been detected and analyzed with the radio holographic (RH) method recently. Reflection signatures in the PD data can also be detected and analyzed with the continuous wavelet transform (CWT) in a strait forward manner, e.g. without requiring any additional information/forward model or reference field. The use of the CWT as an additional tool to analyze PD data is described and the assets and drawbacks in comparison to RH are discussed. Two years of consistent CHAMP PD data have been analyzed with CWT. The signature of surface reflections can be detected successfully. The CWT based method also reveals weak signatures during times when the direct GPS signal is not influenced by the atmosphere and travels only through the ionosphere. Different classes of ionospheric signatures can be isolated. The geographical distribution of each signature class reveals different patterns. Such observations may contribute to investigations of ionospheric structures like sporadic E or spread F layer.