2.3. Instrumentation/Specifications
INTERMAGNET does not specify the type of magnetometer that must be used (although a list of instrument suppliers can be provided on request), however an IMO must try to meet the recommendations listed below. These specifications are used by INTERMAGNET as a guideline for reviewing data quality when data are either submitted for an IMO application, or when definitive data are submitted for inclusion in the INTERMAGNET archive. A scalar magnetometer is not mandatory, but is recommended for data quality monitoring.
2.3.1. Definitive Data
Accuracy |
±5nT |
2.3.2. Absolute Measurements
See Chapter 4
2.3.3. Vector Magnetometer
Resolution |
0.1nT |
Dynamic Range |
±4000nT High Latitude ±3000nT Mid/Equatorial Latitude |
Band pass |
D.C. to 0.1Hz |
Sampling rate |
1Hz |
Thermal stability |
0.25nT/°C |
Long term stability |
5nT/year |
2.3.4. Scalar Magnetometer
Resolution |
0.1nT |
Accuracy |
1nT |
Sampling rate |
0.033Hz (30 sec) |
2.3.5. Clock Timekeeping
Observatory data logger |
5 seconds centered on UTC minute (mm:00) |
Data collection platform |
±1.5 sec GOES, GMS ±1.0 sec METEOSAT |
2.3.6. Recorder
An on-site recorder is necessary so data are not lost as a result of data transmission outages.
2.3.7. Transmission
Transmission to a Geomagnetic Information Node (GIN) must be over the Internet or by satellite, within 72 hours of acquisition or sooner (see Section 6.1.4 ).
Note
Keeping within the time slot for satellite transmission is an important duty of an IMO operator. When advised by a GIN of a time drift, the IMO operator must make the necessary corrections within 24 hours.
2.3.8. Other
Preliminary data |
transmitted in IAGA2002 format (IMFV2.83 for satellite) |
Definitive data |
to be submitted annually for inclusion in the IRDS in IAFV2.11 format |
Instrument baseline data |
to be submitted annually for inclusion in the IRDS in IBFV2.00 format |
Annual means |
to be submitted annually for inclusion in the IRDS in IYFV1.02 format |
Filtering |
to INTERMAGNET standard (Section 2.4 ) |
For more information see Section 6.1.1 for Data Formats and Section 6.1.2 for Data Types.
2.3.9. Proton Gyromagnetic Ratio
In 2009, INTERMAGNET adopted the new proton gyromagnetic ratio (for H2O, sphere, 25°C) published by the CODATA group in 2006 (see https://physics.nist.gov/cuu/pdf/all_2006.pdf ):
This ratio divided by 2 pi relates the magnetic field strength in T to the output frequency (Larmor frequency) of a proton magnetometer in Hz. For example, a field strength of 50000.00 nT gives a Larmor frequency of 2128.819 Hz.