| dc.description.abstract |
This study establishes an empirical model to describe ionospheric scintillations of the L-band S4-index. Existing scintillation models have been developed by limited data of a single satellite and/or ground-based radar and satellite receiver observations over the continent, which are restricted by both coverage and temporal resolution. To resolve the above short coming, some models are constructed by combining various satellite, receiver, and radar observations. However, frequency bands from various observations seriously result in the scintillation property being difficultly studied. Note that most of the existing scintillation models have been developed based on VHF (30-300 MHz) frequencies. Today, the most popular frequency band for satellite positioning, negation, and communication applications is the L-band (1-2 GHz, the GNSS (global navigation satellite system) broadcasting frequency). Therefore, it is essential to develop an L-band scintillation to meet and support daily usages and applications. Six microsatellites of the joint Taiwan-US satellite constellation mission, termed FORMOSAT-3/COSMIC (F3/C), were successfully launched in to a circle low Earth orbit at 01:40 UTC on 15 April 2006. Each satellite houses a GPS occultation experiment payload globally deriving the vertical profile of scintillation S4 index in the ionosphere. This constellation provides instantly more than 2000 ionospheric scintillation S4 index profiles 90-800 km altitude. Dense global scintillation S4 index probing brings a new era for studying the space weather in the ionosphere. The empirical model is developed to simulate the S4 index on the ground by using about the maximum value (S4max) on each 12 mega F3/C S4-index profiles during 2007-2014. Since the scintillation inhabits prominent diurnal, seasonal, geographic, and solar activity variations, the variations are treated to be independent to each other, and the model can be constructed by multiplying the variations altogether. The constructed model could well reproduce the F3/C S4-index probing, and yield good agreements with results of in-situ irregularity observations by satellites and ground-based receiving satellite signals. These confirm that the model can be used to forecast global L-band scintillations on the ground and in the near surface atmosphere.
Instead of the S4max, when the whole information of the F3/C S4 index profile is used, the model is further able to predict the occurrence probability for given a scintillation intensity observed on the ground. The S4 index intensity on the ground converted from the whole profile is similar to that observed by co-located ground-based GNSS receivers, while for S4>0.15 and S4>0.2, the occurrences of the two are also highly correlated. Based on the F3/C S4-index profiles, the empirical model is constructed to predict the intensity and the occurrence probability of the L-band S4 index on the ground of the globe, which shall benefit satellite communication, positioning, and navigation applications. | en_US |