Software codes for Fourier spectral analysis and decomposition.

Description of Discrete Fourier Transform (DFT) tools for spectral analysis and filtering of along-track LEO satellite ionospheric observations and long-term time series of satellite and ground-based ionospheric observations.

Generally, DFT-based approach to satellite data and long-time series comprises of four parts, which due to different data acquisition domains differs between the along-track data and time series. It also doesn’t exactly correspond to number of tools, because there are some codes combining two parts of the analysis (e.g. detrending for high-pass filtering and band-pass filtering). The analysis comprises of:

·         Auto-spectral time-frequency analysis of ionospheric and ancillary data by short-term Fourier transform (STFT) preceded by data detrending (high-pass filtering)

·         Cross-spectral analysis of ionospheric and ancillary data by STFT

·         Band-pass filtering with Butterworth filter and generation of high-level data

·         Correlation analysis

1.      Codes for satellite data analysis

stft_SPEC_SwarmNe and stft_SPEC_SwarmB – time-frequency analysis and auto-spectrograms of Swarm electron density (Ne) and ancillary magnetic (B) field components in instrumental coordinate system.

stft_CROS_SwarmNe_SwarmB – time-frequency cross-spectral analysis and cross-spectrograms between Swarm Ne and ancillary B field components.

stft_FILT_SwarmNe and stft_FILT_SwarmB – band-pass filtering and generation of high-level data from limited frequency bound, but also generation of low-pass filtered trend for data detrending before time-frequency analysis. The code has twofold applicability as the applied type of filter is of the same kind.

stft_SERIES_SwarmNe – generation of yearly time series from Swarm Ne data by selection of 4 orbital track parts nearby selected location and averaging. The correlation analysis of these series can be considered, but inhomogeneity of longitudes and times of sampling is large, and makes them in fact an approximation of time series in statistical sense.

ssgrid_tvec01 – generation of nigh/day terminator used for plotting. This code woks in combination with sunrise.m code provided by François Beauducel at Mathworks website (https://www.mathworks.com/matlabcentral/fileexchange/64692-sunrise-sunrise-and-sunset-times?s_tid=srchtitle_support_results_1_sunrise+code)

OLP_NOT1_EFIA_LP_1B_20151231.mat – example of selected preprocessed orbits of Swarm Ne data downloaded from https://swarm-diss.eo.esa.int/

OVF_NOT1_MAGA_LR_1B_20151231.mat - example of selected preprocessed orbits of Swarm B data downloaded from https://swarm-diss.eo.esa.int/

All_boundaries – tectonic plate boundaries used in plotting, downloaded from data webpage: https://github.com/lcx366/PlateTectonic.

2.      Codes for time series analysis

stft_SPEC_VTEC_sol_mag - time-frequency analysis and auto-spectrograms of VTEC calculated from phase GNSS data of selected IGS stations, Dst geomagnetic index, and two parameters of solar wind derived from OMNI database: solar wind dynamic pressure (denoted here as Psw) and interplanetary magnetic field (IMF) total strength (Bt).

stft_CROS_VTEC_sol_mag - time-frequency cross-spectral analysis and cross-spectrograms between VTEC, and space weather parameters (Dst, Psw and Bt).

stft_FILT_VTEC_sol_mag - band-pass filtering and generation of high-level data from limited frequency bound, but also generation of low-pass filtered trend for data detrending before time-frequency analysis. The code has twofold applicability as the applied type of filter is of the same kind. The code calculates all quantities for all data types simultaneously.

stft_CORR_VTEC_sol_mag – calculation of Pearson Correlation Coefficients (PCC) between band-pass filtered (high-level) VTEC and space weather parameters using arbitrary division of their yearly time series.

G2015.mat – example station-based VTEC data (selected IGS stations across the globe)

Sta_BLdv_2015.mat – station names and geodetic coordinates

dst1960_2022.mat – preprocessed Dst time series from the Data Analysis Center for Geomagnetism and Space Magnetism, Graduate School of Science, Kyoto available at: http://wdc.kugi.kyoto-u.ac.jp/dstdir/.

solar19952024.mat – preprocessed OMNI datasets of solar wind parameters downloaded from https://spdf.gsfc.nasa.gov/pub/data/omni/ (contact: Papitashvili N.).