IBFV2.00 INTERMAGNET Baseline Format

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This file format is to be used to provide baselines for use in examining equipment and environmental quality (mainly thermal stability of the variometers) and for inclusion on the INTERMAGNET yearly DVD. This format makes room for all published components, including a baseline to scalar data. After a one-line header, the first section contains the observed baseline values on the days when they are measured. Consequently the number of entries will depend upon the schedule for absolute measurements at the observatory. The second section contains adopted baseline values, representing each day of the year. The third section for comments is mandatory. This comment section must include a brief description of the baseline adoption method.

File name: obsyyyy.blv e.g. bfe2008.blv


Component values are coded as signed float numbers, right justified with format (1X,F9.2). DeltaF values (denoted as DDDD.DD) are coded as signed float numbers, right justified with format (1X,F7.2). The field widths must be maintained, either through zero-filling or space-filling in order to have records of fixed length: every line is 43 characters long in section one, and 53 characters long in section two excluding terminator CrLf or Lf.

Comment lines should not exceed 53 characters long.

Description of IBF parameters
Parameter Description
COMP Order of components XYZF, DIF_, HDZF, UVZF (see Note 1).
HHHHH Annual mean value of H component in nT.
FFFFF Annual mean value of F component in nT.
IDC Official IAGA three-letter station code in capital letters.
YEAR 4-digit Year: eg, 2009
DDD Day of the year
aaaaaa.aa Observed baseline of X, D, H or U in nT or minutes (absolute – variometer)
bbbbbb.bb Observed baseline of Y, I, D or V in nT or minutes (absolute – variometer)
zzzzzz.zz Observed baseline of Z or F in nT (absolute – variometer)
ssssss.ss Observed baseline of Scalar F in nT (absolute – scalar, See Note 5)
AAAAAA.AA Adopted baseline value of X, D, H or U in nT or minutes.
BBBBBB.BB Adopted baseline value of Y, I, D or V in nT or minutes.
ZZZZZZ.ZZ Adopted baseline value of Z, or F in nT.
SSSSSS.SS Adopted baseline value of Scalar F in nT. (absolute – scalar, See Note 5)
DDDD.DD Representative value of Delta F for this day (see Note 2)
m Discontinuity marker (valid values c or d – see Note 3).
* Section separator
_ Indicates a space character
CrLf Indicates a Carriage return, Line feed

File name convention is IAGYR.BLV where IAG = 3-letter observatory IAGA code and YR = 2-digit year.


  1. The codes XYZF, DIF_, HDZF,UVZF are the only supported codes of the components which must be listed in specified order within sections one and two.
  2. ΔF is defined as ΔF = F(v) - F(s). Where F(v) represents the total field value calculated from the main observatory instrument ("vector F") and F(s) represents the total field from an independent instrument ("scalar F"). Both F(v) and F(s) must be corrected to the location in the observatory where geomagnetic absolute observations are made.
  3. Discontinuity marker: c indicates that the baselines for all components form a continuous series with the previous day, d indicates a discontinuity in the baseline of one or more components (i.e. step) between the current day and the preceding one. This is to allow the baselines to be plotted at an appropriate scale. A discontinuity is defined as a known operational change such as an instrument re-alignment.
  4. Missing values must be replaced by 99999.00 for D,H,X,Y,Z,F and by 999.00 for ΔF. Components that are not observed, which may include Scalar F (SSSSSS.SS) and Delta F (DDDD.DD), must be coded 88888.00 and 888.00 respectively.
  5. The observed and adopted F baselines represent the DIFFERENCE in the F component between the absolute position and the continuously recording scalar instrument.