[obspy-users] Question about PPSD output value by default (without using special_hanging parameter).

Tobias Megies megies at geophysik.uni-muenchen.de
Thu Jun 25 12:00:39 CEST 2020

Basically, no matter what units your input data, the metadata should
correctly specify how to get to physical units from that starting point.

Usually raw data are in counts and the metadata specifies how to get
from counts to velocity in m/s or to acceleration in m/s**2 in case of

If your data already is in e.g. velocity in m/s, you ideally should set
up a proper response, basically stating input and output units are both
m/s and that nothing has to be done, e.g. have a look at this ticket, to
get an idea what i mean:

hope it helps,

On 24/06/2020 20:00, Gbehou Ange Amour Soupplian wrote:
> Hello,
> I would like to analyse ambient noise from different instruments
> (Geophone, BroadBand, accelerometer..) by using ObsPy's PPSD. It is
> therefore necessary for me to have the same unit for the PSD estimation
> in order to compare them (from different instruments).
> For example if my raw data are in velocity (geophone sensor), does ppsd
> estimation automatically convert it into acceleration, as it shows
> [*(m/s²)²/Hz*] [db] when we plot ? Then what if raw data are in
> acceleration (accelerometer sensor)?
> Best regards.

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