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Fundamentals of FGM Data
Data Types

Fundamentals of FGM Data

The FGM instrument samples data internally at a rate of approximately 201.75 vectors/second, this decimated by different amounts, depending on the instruments mode, which itself is dictated by the spacecraft telemetry mode. The following table details the most commonly used telemetry type.

Instrument Mode	Mode Name	Primary Vectors per second	Secondary Vectors per second
C	Normal Mode	22.4	3.0
D	Burst Mode	67.3	7.8
E	Extended Mode	0.25	0	Data recorded to the instrument internal memory.
All	Housekeeping	0.19	0.19	One unfiltered 8-bit values per housekeeping packet.

At all data rates, the data can be returned over six different magnetic field ranges. At the start of the mission only ranges 2, 3 and 4 were used, but as the Cluster orbit has evolved to lower altitudes, and hence higher magnetic field, ranges 6 and 7, never designed for science operation, are now used routinely The sensor ranges differ in the span of magnetic fields which they cover, and in their resolution, the following table details the possible ranges, and their parameters.

FGM operating ranges

Range	Maximum range (nT)	Minimum range (nT)	Resolution
7	+65528	-65536	8 nT	Designed for ground testing
6	+16,376	-16,385	2 nT
5	+4095.5	-4096.0	500 pT
4	+1023.775	-1024.000	125 pT
3	+255.969	-256.000	31.25 pT
2	+63.992	-64.000	8 pT

The plots below show a week of operations from June 2001, the different types of data are colour coded, so Normal Science Data is in Green, Burst Science Data is in Blue, Extended Mode Data is in Red, and where nothing else is available, Housekeeping Data is shown in Grey. The time line at the top also shows some details such as the orbit number (from Orbit 151 to 153) and the time of Perigee, Apogee, and inward & outward passage into the Magnetosphere.

Data Types

There are a number of different data products available, some are only used internally within the FGM operations and science teams, others are more widely available.

FGM data in the ESA Cluster Active Archive (CAA)

The aim of the CAA is to generate a repository of all Cluster data, from all instruments at their highest time resolution, of the highest scientific quality that the teams are able to generate. Therefore all FGM data are in the process of being recalibrated and reprocessed and submitted to the ESA. Three primary datasets are available: full resolution (at either 22 or 67 vectors/second), data averaged to 5 vectors/second and a spin averaged data set.

ESA Cluster Active Archive

Prime Parameter Data Set

The Prime Parameter Data Set is spin averaged data for all the spacecraft. The calibration for this data set is generated soon after the data have been taken, generally with a lag of only a few months, and are widely used not just for data browsing and interval selection, but also for a broad range of scientific investigations. They are freely available through the Cluster Data Centers, and are also archived at the CAA for completeness.

Cluster Data Centers

Summary Parameter Data Set

The Summary Parameter Data Set is one minute averaged data for a single spacecraft (the "reference spacecraft", normally spacecraft 3). The Summary Parameter Data is available to anyone, but is of limited use for scientific analysis.

Both Prime and Summary Parameter Data Sets are available from your local data centre, click on the link for the Cluster Data Centres to find out which Data Centre you should be using.

Cluster Data Centers

When none of the above data types are available, other data may be available, such as Extended Mode, or Housekeeping. Generally the fidelity of this data is much lower, and it is normally only suitable for contextual use.

Data Links

ESA CAA
Prime Parameter Data Download
Cluster Data Centers
UK Cluster Data Center
FGM Principal Investigator Dr Elizabeth Lucek

Data Products

Data Products

FGM operating ranges

Useful Links