Seismic Precursors project has been developed with hard work of:

The seismic precursors analysis is an important scientific research domain. It tries to prevent earthquake by very low frequency emissions analysis. More about the project...

The on line observatory makes available a couple of sensitive VLF receivers, installed in a low-noise location. This provides an ideal condition to listen to VLF signals directly from your home, avoiding the need to do on field expeditions.

What we can do with the VLF on-line observatory.

  1. to listen to live signals, by using a legacy audio player like Windows Media Player, Winamp or VLC; it is just like to listen music from a web radio;
  2. to make real time signal analysis, by using the audio player and a software like Spectrum Lab; there are many kinds of plots that can be generated (e.g. spectrum analysis, spectrograms and levels plotting);
  3. to analyze and process the signal in real time (e.g. filtering the signals to highlight the presence of particular traces, submerged by natural noise), by using a player, VAC (Virtual Audio Cable) software and Spectrum Lab;
  4. to record signals from the live stream, creating a personal archive, by using a player to reproduce the signal and Spectrum Lab or Audacity to record the audio on a file;
  5. to make post-analysis of the signals, by accessing your personal archive or the on-line repository; in this case the it is possible to use both Audacity and Spectrum LAB (remember that you need to convert mp3 files into wav format in order to use them with Spectrum LAB).

Example one.

Waveform analysis of a 3 seconds natural radio signal. The signal is represented as a function of the time: showing how it evolves in the time domain. (Created with Audacity.)

Example two.

Spectrogram analysis of 10 s natural radio signal: the most complete representation we can do of a signal. It shows how the spectrum of the signal evolves in the time domain. In this picture we can identify: storms radio signals, hum radio noise, people made noise (e.g. household), radionavigation signals and military radio teletype transmissions. (Created with Audacity.)

Example three.

Another spectrogram using colors. The represented signal (the curve in the center) is a whistler: it has been originated in South Africa, traveled throw the free space out of the atmosphere for many thousand of kilometers and reentered in Europe where it has been received. (Created with Audacity.)

Example four.

A spectrogram of a multiple whistler. Also a frequency spectrum (on the right) and waveform (on the top) are represented. (Created with Spectrum Lab.)

Example five.

A 3-dimensional spectrogram, representing the signal coming from some storms during the summer. (Created with Spectrum Lab.)

Example six.

A multi-strip recording. This kind of plot is similar to the one used in seismic observatories. It gives a draft but complete representation about time evolution of the signal. A single plot can represent up to 15 minutes of evolution. (Created with Spectrum Lab.)

Example seven.

Many channels can be configured as in the old strip chart recorders where each channel represents a different feature. This kind of analysis is useful to see long time signal evolution. (Created with spectrum Lab.)

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