The IRIS SACPZ web service returns the poles and zeros of the selected instrument responses in SAC ASCII format.
Metadata may be selected based on network, station, location or channel names in addition to time.
Web service clients that use ws-sacpz can be found at the “Clients list”/clients/. In particular the FetchData script will request SAC Poles and Zeros from ws-sacpz and write them to channel-specific files.
The ws-sacpz service allows data selection using the following parameters (see the service interface for detailed usage):
- network, station, location and channel
- time and duration
Data for a single epoch, multiple epochs or no data may be returned depending on search criteria.
Wildcard support for locations and channels
The service supports the use of * and ? in specifying search criteria for locations and channels. The * wildcard is used to match any combination of characters while ? is used to match one character only. They can be used at the beginning, middle or the end of the search criteria. For example: loc=1*, chan=B*Z or chan=B?Z.
Combined or multiplexed responses
This service will return all of the selected responses for a single request in a single returned stream, this can contain any number of locations, channels and time ranges. If multiple responses are saved in a single file many SAC PZ parsers will not recognize that multiple responses are included.
The DMC’s web service Fetch scripts will make a request for each channel individually and save the response(s) in separate channel-based files; this output might still contain multiple responses for different time ranges, which is a convention that recent SAC releases can handle by using the included annotations.
Annotations as comments
Each set of poles and zeros will be annotated (using comment lines) with details that identify the associated time series and other related metadata. The comment structure is in a style developed by Dr. Robert Herrmann.
Incident angle (dip) convention
The value of the component DIP in the annotations is in the SAC convention for incident angle, specifically degrees from vertical. This is not the same as the SEED convention for dip.
Conversion from Hertz to radians/second
Pole and zero locations will be converted from Hertz to radians/sec when necessary to conform to SAC conventions. The normalization factor (A0) will also be changed during this conversion, which consequently changes the value of CONSTANT in the output.
Conversion to displacement response
The response will be converted to displacement when the original input units match known unit types for velocity or acceleration. The appropriate number of zeros will be added at the origin as part of the conversion to displacement. The input units string in the annotated comment field will be modified appropriately to match the units represented by the poles and zeros. Only the time dimension is modified when converting from velocity or acceleration to displacement, the length dimension is not modified (e.g. Meters are not changed to Nanometers).