Metadata include station siting, instrumentation, and earthquake information which serve to enhance and support our waveform data archives.
Dataless SEED is a subset of the SEED data format, and includes instrument responses, instrument coordinates, compression type, etc.. A dataless volume is commonly used to populate a metadata database or in combination with MiniSEED to convert time series to an alternate format such as full SEED (using the IRIS DMC’s rdseed software).
A modern alternative to dataless SEED volumes to exchange seismological metadata is the FDSN’s StationXML schema.
SAC Poles and Zeros
A SAC Poles and Zeros file is used to provide instrument response metadata for timeseries data in SAC format.
See this screencast.