# PSD for Hydrophone

**URL:** <https://discourse.obspy.org/t/psd-for-hydrophone/1766>\
**Category:** Usage Questions\
**Created:** [August 10, 2023, 8:47am UTC](https://discourse.obspy.org/t/psd-for-hydrophone/1766 "2023-08-10T08:47:00Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![seismo2112](https://discourse.obspy.org/user_avatar/discourse.obspy.org/seismo2112/32/728_2.png) [@seismo2112](https://discourse.obspy.org/u/seismo2112)\
**Post date:** [August 10, 2023, 8:47am UTC](https://discourse.obspy.org/t/psd-for-hydrophone/1766/1 "2023-08-10T08:47:00Z")

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HI All,

I am trying to plot PSD for hydrophone, though there is no instrument response available. I tried obspy PPSD object but it requires pole information. Can anyone suggest something?

Lalit

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**Author:** ![megies](https://discourse.obspy.org/user_avatar/discourse.obspy.org/megies/32/9_2.png) [@megies](https://discourse.obspy.org/u/megies)\
**Post date:** [August 17, 2023, 9:21am UTC](https://discourse.obspy.org/t/psd-for-hydrophone/1766/2 "2023-08-17T09:21:29Z")

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You can check this post for a related issue: [Metadata entries for PPSD when using hydrophone data](https://discourse.obspy.org/t/metadata-entries-for-ppsd-when-using-hydrophone-data/1720)

If your instrument response is indeed flat unity (which seems doubtful.. but maybe your data has already been corrected for the frequency response of the recording system?), you could create some unity metadata and use that.

You could download an example unity metadata from NRL and manually adjust it:  
[http://service.iris.edu/irisws/nrl/1/combine?instconfig=sensor\_GenericUnity\_UnityVelocity\_LF0\_SG1\_STgroundVel:datalogger\_GenericUnity\_UnityDatalogger\_FR40&format=stationxml](http://service.iris.edu/irisws/nrl/1/combine?instconfig=sensor_GenericUnity_UnityVelocity_LF0_SG1_STgroundVel:datalogger_GenericUnity_UnityDatalogger_FR40&format=stationxml)

Or you could follow [our related tutorial](https://docs.obspy.org/master/tutorial/code_snippets/stationxml_file_from_scratch.html) to do the same in python.