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spedas / bleeding_edge

IDL-based Space Physics Environment Data Analysis Software (bleeding edge)
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Help request on THEMIS twavpol #2 #62

Closed ericthewizard closed 1 year ago

ericthewizard commented 1 year ago

I received another help request on THEMIS twavpol:

I want to know when we use the twavpol for the themis probes (b,c). In the tplot, the color bar shows the different parameters of the waves, but I can't figure out what is on the v-axis(as highlighted in the attached figure with red lines). if it's frequency, then why does it only show a range of 0 to 8? but in FFT tplot the frequency range is up to 3000.

Please explain to me what parameter is on this axis and whether we can convert it to frequency[Hz].

2021-02-08_TWP-1

jameswilburlewis commented 1 year ago

The y-axis is indeed frequencies in Hz. FGL data for THEMIS-B on this date has a cadence of 16 samples/sec, so the FFT frequency bins cover the range from 0 to the Nyquist frequency = 8 Hz.

The onboard FFT data is collected from the SCM instrument at much higher sample rates, so the frequency range will be correspondingly larger.