3.1. Description
Because of recent developments in instrumentation, data acquisition, and data dissemination, an increasing number of observatories have begun to produce a filtered one-second data product in addition to traditional one-minute data, hourly means, daily means, monthly means, and annual means. An INTERMAGNET survey of the user community carried out in 2005 concluded that there is a desire for one-second data, that they should be made available through the INTERMAGNET network, and that, as is the case for one-minute data, a standard of instrument performance and data quality should be set. The INTERMAGNET Observatories & Standards Subcommittee has developed one-second data standards which were adopted in 2012 [1] . These standards are discussed in the following sections.
A one-second INTERMAGNET Magnetic Observatory (1s-IMO) is a magnetic observatory with full absolute control, making continual data recordings at a minimum rate of once per second using a vector magnetometer and at a minimum rate of once every 30 seconds using a scalar magnetometer. Since vector measurements performed by a continually recording magnetometer are typically variation measurements, they are to be corrected to quasi-absolute using the best available baseline measurements prior to transmission.
1s-IMOs are required to transmit preliminary data in an INTERMAGNET recognized format (see Section 6.1.1) to one of the INTERMAGNET Geomagnetic Information Nodes (GIN) by electronic means within 72 hours of recording. Data are typically transmitted over the Internet such that preliminary data can be made available on the INTERMAGNET web site. Note that, for the time being, GINs also accept reported data from observatories that have historically transmitted such data.
Within 3-months, observatories may transmit quasi-definitive data to one of the INTERMAGNET GINs provided these data meet the provisional baseline conditions outlined in APPENDIX A. Quasi-definitive data submission is by the same method as preliminary data submission (described in Section 6.2). Observatories may submit quasi-definitive data in place of preliminary data if this meets the requirement of being received within 72 hours of recording.
At the end of a calendar year, until the production of a global one-second data archive, one-second data are to be prepared using final baselines and submitted as definitive data for inclusion in the INTERMAGNET archive. The deadline for submission will be communicated by INTERMAGNET. Definitive data archives are made available on the INTERMAGNET web site. For definitive data processing, it is recommended that the same variometer baselines computed for the one minute be used for the one second, if the same variometer is producing both data sets.
An observatory intending to participate in INTERMAGNET as a 1sIMO must agree to these conditions for data transmission and be able to meet the INTERMAGNET standards for one-second data detailed in this chapter. Chapter 8 provides instruction for observatories wishing to make a 1s-IMO application. Further information is also available from the INTERMAGNET Observatories Subcommittee chair.