2012/12/11
An outline of the variations between FDSN-StationXML and SEED 2.4.

This should not be considered complete but highlights the major differences.


Features and content supported by SEED and not in FDSN-StationXML:

* Dictionary and lookup reference blockettes, there are no such concepts
 in FDSN-StationXML.

* Data record blockettes, 100 and higher.  FDSN-StationXML does not include
 anything that would be included in miniSEED.

* Event and time span indexing blockettes.  No event parameters and no
 indexing relating to data records in files are contained in
 FDSN-StationXML.

* Comment code keys, class code and units of comment level (blockette 31
 referenced by 51 and 59).  FDSN-StationXML contains comments but does not
 retain these rather esoteric features.

* Generic Response Blockette 56, a simple response defined by a list of
 corner frequencies and corner slopes, documented as not acceptable on their
 own and should be combined with other response blockettes.  This blockette
 is not used by any metadata at the IRIS DMC, likely it is not widely used
 or ever used at all.


Features and content supported by FDSN StationXML and not in SEED:

* Instead of the instrument identifier field of blockette 52,
 FDSN-StationXML has structures at the Channel level for describing a
 Sensor, Preamplifier and Datalogger with many details for each component
 such as manufacturer, vendor, model, serial number, etc.

* Uncertainties for latitude, longitude, elevation, depth, azimuth, dip
 and frequency.

* Start times and end times are allowed at the Network level, in addition
 to the Station and Channel levels.  The start times are required but the
 end times are optional, allowing for currently operating epochs.

* Comments are allowed at the Network level, in addition to the Station and
 Channel levels.

* Optionally specify a sampling rate as a ratio in addition to a required
 value in samples per second.

* Name and description fields for each response filter type, similar to the
 name field for blockette 61 but broadened to all response structures.

* Station and Channel entries may contain an ExternalResource element to
 indicate a URL to an external report or dataless or other relevant
 documentation.

* Station and Channel entries can contain CreationDate and TerminationDate
 attributes.  These are independent of the start and end dates that define
 the epoch.

* A Station entry can include one or many Equipment elements to list the
 equipment common to all channels at a station.

* A Station entry can contain a Site element that includes: name,
 description, town, county, region, country.

* A Station entry can include Vault and Geology descriptions.

* A Station entry can include one or many Operators.  Each Operator
 designation can include an agency name, a web site and contact details.

* A Contact element, used for Operators or comment Authors, can contain
 name, agency, email and phone number.

* A Comment can include an Author designation.

* An alternateCode and historicalCode may be designated in addition to the
 "code" for a Network, Station or Channel.

* A generic description string is supported for Network, Station and Channel
 elements.

* The storage format can be denoted for Channels as a simple string
 (e.g. SEED, V0, etc.)

* The restriction status (open, closed or partial) can be denoted for a
 Network, Station and Channel levels.

* A resource identifier can be associated with Equipment and response filter
 entries.  This can be used to identify equipment in an inventory system or
 entries in a catalog of response filters.

* Using a schema extension, the time series data availability can be
 described for at the Network, Station and Channel levels.  Availability
 can be described as either extents or a subset of spans.
