VLF Spectrograms up to 1.5kHz from Kannuslehto VLF campaigns 2008-2024 during enhanced geomagnetic activity

This data set is created from the analysis result of Kannuslehto VLF campaigns 2008-2024 for the PLHR study in manuscript Drastichová et al.: "Geomagnetically Induced Currents on Power Line Harmonic Radiation Observed at the Kannuslehto Ground-Based Station" accepted to JGR: Space Physics. The event selection criteria for the data set for the study has been geomagnetic field variation (dH/dt) reaching 200nT/min threshold. The event time intervals include data before and after the threshold is reached. The data set covers 22 periods from available Kannuslehto VLF campaigns 2008-2024.

The published VLF spectrograms are in 1 hour files in HDF5 format including spectrum data, calibration and other attributes related to the station and used analysis. The published spectrums have 2 seconds time resolution covering frequency band up to 1.5kHz with 1Hz frequency resolution forming 1501 x 1800 (frequency x time) matrix per hour. The calibration factors to SI units, frequency and time information are included in each HDF files.

The source data for published spectrums are 4 minutes long 1s resolution sequences of the total power spectrum matrices from the SGO VLF analysis package written by Tauno Turunen, SGO. These matrices are generated with FFT length of 78126 points with 39064 point overlap using a specific signal filtering like saturation and peak and sferics removal.

The broad-band VLF raw data is recorded from two orthogonal antenna system built at SGO known as "VLF 100aT system". The timing is based on GPS 10MHz reference. The loop aerials are oriented in NS and EW directions. The 24-bit raw data is sampled with 78125Hz.