The targets web service returns a list of targets having measurements for the specified metric. Targets can be filtered by station, network, etc. This channel list can be passed to the measurements service using command line tools such as curl.
The targets service returns a text list of networks, stations, location codes, channels and quality indicators that have measurements for metrics available through the measurements service. For summaries of each metric and links to more detailed documentation, select the Current list of all metrics button above.
Specifying channels is optional (but recommended) for the targets service. When channels and times are absent from the query, the service returns a list of all targets with any measurements for the requested metric(s). If channel options are included, the service will only return a list of targets having any requested metric measurements matching the specified channels.
There are two ways to define desired channels when requesting a targets list:
- target – labeled as N.S.L.C.Q (SEED Network.Station.Location.Channel.Quality)
- SNCLQ filter – where the SNCLQ (SEED Sta[tion], Net[work], Chan[nel], Loc[ation] and Qual[ity]) are listed as separate key/value parameters in any order:
SNCLQ filter parameters are optional. Omitting a parameter (e.g. channel) is equivalent to wildcarding (&channel=*) and returns targets that match any name.
Both channel options accept virtual networks, such as _GSN, but the station name is ignored and a list of targets including all stations is returned. An exception to this occurs when a station list is provided – the targets service returns an error.
All SEED data in the IRIS archive is now stored as M-quality (merged) data. It represents the most complete and best-quality version of the original data received. All measurements except the latency measurements are calculated using archived data, and so have quality M. Latency metrics run on real time data before it is archived and has quality D or R.
It’s possible to choose which HTTP status code the service returns when the query is successful but there is no data to return. Although status code 204 is defined as describing this case, browsers receiving status code 204 do not refresh their previous contents, so it can be difficult to tell that the query completed successfully. Selecting status code 404 when there is no data to return causes the browsers to refresh and display a blank or nearly blank page. Note that the
URL Builder always appeands
&nodata=404 to each query.
Using target Lists in Queries
One practical use of the targets service is to generate a SNCL (Station, Network, Channel, Location code) list file that can then be fed to the measurements service when sending queries on the command line. For instructions and examples, please refer to the command line usage section of the measurement service help page.