SACPZ Web Service

Description

The NCEDC 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 ncedcws-sacpz can be found at https://service.iris.edu/clients/. In particular the FetchData script will
request SAC Poles and Zeros from ncedcws-sacpz and write them to channel-specific files.

Metadata selection

The ncedcws-sacpz service allows data selection using the following parameters:
* 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 NCEDC 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 value of the component dip in the annotations is in the SAC convention. The comment structure is in a style
developed by Dr. Robert Herrmann.

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).