# Study of the Ionospheric Scintillation Radio Propagation Characteristics with Cosmic Observations
## 2 Data and Methods  
### The Data Presentation  
The COSMIC-1 project is composed of six small satellites equipped with GPS occultation experimental devices, ionospheric photometers and three frequency beacons. It has a strong tracking ability for ionospheric scintillation. The data used in this work were collected from the GPS occultation observations provided by historical data from 2010 to 2019 in solar cycle 24, which are archived in the COSMIC Data Analysis and Archive Center (CDAAC). The COSMIC scnlv1 datasets, which contain the amplitude scintillation index (S4) and the SNR for each occultation event, are selected. Data preprocessing is implemented, including data integrity inspection, data extraction and transformation, error filtering and data classification. The amplitude scintillation index and L1 band SNR are extracted. The S4 maximum value (S4 max) in 9 s along with its corresponding tangent height, latitude and longitude are recorded. The COSMIC space-borne GPS receiver does not directly measure S4; it only records the mean square root value of signal intensity fluctuation per second obtained by L1 frequency point 50 Hz carrying noise ratio data. S4 is calculated by CDAAC after the data are transmitted to the ground. Thus, errors in S4 are extracted during data preprocessing. According to [39], the amplitude of the negative fluctuation of the signal cannot exceed the signal strength, and the amplitude of the positive fluctuation cannot exceed the mean value of the signal for a long time. For the convincing aspect of the analysis, the range of S4 is set between 0.3 and 1.5, eliminating S4 larger than 1.5. The threshold of occultation scintillation is set to 0.3 since a scintillation intensity below 0.3 is of little significance to this work. The S4 values are further normalized to make them suitable for statistical modeling and intensity comparisons. After normalization, the scintillation intensity is then classified into different levels, i.e., very weak, weak, moderate and strong (Table 1). In previous studies, the signal amplitude was derived by the carrier-to-noise ratio (CNR). Because it is difficult to determine the CNR and bandwidths for COSMIC data, the SNR is used and normalized to extract the distribution of the signal amplitude. To exclude noise interference, an SNR higher than a threshold of 15 dB is considered and further processed. When the amplitude distribution in relation to S4 is computed, the SNR is classified by the given S4 with \(\pm\)0.005 intervals to extract sufficient SNR samples. The narrower interval of S4 variation is more conducive to improving the accuracy of amplitude statistical fittings. Ionospheric scintillation depends on the geophysical locations. The most representative scintillation events are concentrated around geomagnetic latitudes of \(\pm\)20\({}^{\circ}\), where the equatorial ionization anomaly (EIA) exists. The long-distance lateral transmission of occultation signals makes the scintillation observations subject to the integration of electrons with uneven paths, leading to difficulties in judging the precise location of the irregularities that are responsible for scintillation. In this work, the observed S4 from COSMIC data are grouped by tangent geographical latitudes into 0-30\({}^{\circ}\), 30-60\({}^{\circ}\) and 60-90\({}^{\circ}\), representing low latitudes, including the EIA region, middle latitudes and high latitudes, respectively. To characterize the scintillation in vertical aspects, the tangent height is divided into two groups, 100-150 km and 150-500 km, to distinguish the scintillation characteristics between the E and F layers, respectively. The COSMIC observation satellites at different latitudes and different heights are distributed heterogeneously. Thus, simply using the amount of data to analyze the occurrence times of scintillations of different intensities is not appropriate.