Getting waveform data

Users Mailing List Archive
1

Hello obs-py community,

I’m not a seismologist by background, so please forgive some of my naivety!

I’ve been trying to download some waveforms associated with some stations, and as far as I can gather from the docs, this should work:

from obspy.clients.fdsn import Client
from obspy.core import UTCDateTime
client = Client(“ORFEUS”)

t1 = UTCDateTime(2018, 10, 11, 17, 15, 22, 497918)
t2 = UTCDateTime(2018, 10, 18, 17, 15, 22, 497918)

r = client.get_waveforms(‘Z3’,‘A089A’, ‘‘,’’,t1,t2, attach_response=True)

However, this returns an error:

Traceback (most recent call last):
File “”, line 1, in
File “/Users/chris/.local/share/virtualenvs/arch-NdiSQAf2/lib/python3.7/site-packages/obspy/clients/fdsn/client.py”, line 830, in get_waveforms
data_stream = self._download(url, use_gzip=False)
File “/Users/chris/.local/share/virtualenvs/arch-NdiSQAf2/lib/python3.7/site-packages/obspy/clients/fdsn/client.py”, line 1382, in _download
raise_on_error(code, data)
File “/Users/chris/.local/share/virtualenvs/arch-NdiSQAf2/lib/python3.7/site-packages/obspy/clients/fdsn/client.py”, line 1706, in raise_on_error
server_info)
obspy.clients.fdsn.header.FDSNNoDataException: No data available for request.
Detailed response of server:

(note that the ‘detailed response of server’ is null!)

I thought that this network/station combination was valid because if I run

for n in client.get_stations(): print(b)

I get

…
Network Z3 (AlpArray Seismic Network (AASN) temporary component)
…
Stations (66):
…
Z3.A089A (Nesovice, Czech Republic)
…

A couple of things confused me that might be contributing to errors I’m probably making:

  • Client.get_stations() appears to return instances of the Network class, rather than instance of the Station class:

type(client.get_stations()[0])

<class ‘obspy.core.inventory.network.Network’>

which itself contains an iterable containing instances of Station:

type(client.get_stations()[0][0])

<class ‘obspy.core.inventory.station.Station’>

  • The channels metadata doesn’t seem to be available for the calls I’m trying. For example, this only returns empty lists:

for s in client.get_stations():

for n in s: print(n.channels)

and printing an arbitrary channel doesn’t reveal the channel info either, despite all the other metadata being printed:

print(client.get_stations()[0][0])
Station E064 (La Canada de Mira)
Station Code: E064
Channel Count: None/None (Selected/Total)
2009-07-19T15:25:47.000000Z - 2010-10-19T10:55:00.000000Z
Access: open
Latitude: 39.66, Longitude: -1.46, Elevation: 935.0 m
Available Channels:

  • is it possible to list the available channels? Valid channels just seem to a string value - are these defined as constants anywhere?

Any hints as to things I’m doing wrong (or links to docs to help my understanding) would be gratefully received!

Cheers
Chris

2

Hi Chris,

AlpArray waveform data is restricted, you need appropriate credentials. You need to get in touch with the AlpArray people, but if your affiliation/institute is not part of the AlpArray project you might not be able to get the data.
(Station metadata is not restricted, thats why you got those)

cheers,
T

3

Hi Tobias,

Ah, thanks! How do I find out datasets my institution has access to - can I do this programmatically? (and is authentication just IP based or is there a gateway system?)

Cheers
Chris

4

You can exclude restricted stations like this (if the metadata correctly specify the restriction status):

inv = client.get_stations(network='Z3', includerestricted=False)

This will throw an error because no data matches.

Network/Station objects have an ".restricted_status" attribute if you fetch all station data.

I don't think there's an IP filter but you do need credentials for AlpArray, like I already said.

T

5

Thanks - that’s very helpful!

I still see channels(0) when iterating through networks (and stations), even when I use ‘includerestricted=False’; e.g. the last result I get from running for s in client.get_stations(includerestricted=False): print(s) is:

Network VI (SIL Icelandic national seismic network)

Station Count: None/None (Selected/Total)

1990-10-10T00:00:00.000000Z - –

Access: open

Contains:

Stations (6):

VI.ADA (VI-ADA)

VI.ASB (VI-ASB)

VI.FAG (VI-FAG)

VI.GIL (VI-GIL)

VI.GOD (VI-GOD)

VI.SKR (VI-SKR)

Channels (0):

and from running

for s in client.get_stations(includerestricted=False):

for n in s: print(n)

Station SKR (VI-SKR)

Station Code: SKR

Channel Count: None/None (Selected/Total)

1996-10-02T00:00:00.000000Z -

Access: open

Latitude: 64.56, Longitude: -18.39, Elevation: 858.0 m

Available Channels:

is this expected behaviour, or should the list of channels be listed in the metadata?

Chris

6

One can request station information at various hierarchical “levels” to reduce data load. The default level is “station” thus there will be no channel-level information in the requested metadata. Adding level="channel" to the get_stations() call will also request the aforementioned extra information. An even more detailed level is “response”.

Cheers!

Lion