A Filtering Method Developed to Improve GNSS Receiver Data Quality in the CALIBRA Project

To study ionospheric scintillation on L-band radio signals, it is nowadays typical to acquire
data with GNSS (Global Navigation Satellite System) receivers working at high frequency
sampling rate (50-100 Hz). When dealing with such data, it is common to consider the
contribution coming solely from observations at elevation angles, calculated from the receiver
to the selected satellite, above an arbitrary threshold, typically 15-30°. Filtering out measurements
made at low elevation angles helps keeping a high SNR (Signal to Noise Ratio) and
eliminating non-ionospheric related effects, such as multipath.
The downside of that well consolidated method is a reduction of the field of view spanned by
the GNSS receiver antenna, and, if it is the case, of the whole network. This is not crucial for
dense networks or well covered areas, but it can be in the case of not well covered regions, for
logistics (e.g. forests, deserts, etc.) and/or environmental reasons (e.g. oceans). The loss of
information in many applications could be meaningful.
In this paper, we present a method to filter out spurious data based on an “outliers analysis”
able to efficiently remove multipath affected measurements, reducing the data loss from
35-45% to 10-20%. It is based upon the Ground Based Scintillation Climatology (GBSC) and the station characterization based upon GBSC [5] is applied to the CIGALA1/
CALIBRA2 network in Brazil. The research shown herein was carried out in the context of the CALIBRA (http://www.calibra-ionosphere.net) project and exploits the CIGALA/
CALIBRA network in Brazil, to which the method was applied, enlarging the field of view
and, then, improving the capability of inferring the dynamics of the low latitude ionosphere.