NASA IGRF/DGRF. Model of geomagnetic field.
The International Geomagnetic Reference Field (IGRF) model is the
empirical representation of the Earth's magnetic field recommended for
scientific use by a special Working Group of the International
Association of Geomagnetism and Aeronomy (IAGA). The IGRF model
represents the main (core) field without external sources. The model
employs the usual spherical harmonics expansion of the scalar potential
in geocentric coordinates. The IGRF model coefficients are based on all
available data sources including geomagnetic measurements from
observatories, ships, aircrafts and satellites. The main web-page of
the model is
modelweb.gsfc.nasa.gov.
The IGRF model consists of sets of coefficients for a global
representation of the Earth magnetic field for the years 1945,
1950, 1955, etc. There are definitive coefficient sets (DGRF##.DAT)
for which no further revisions are anticipated and IGRF##.DAT and
IGRF##S.DAT for which future updates are expected. IGRF##S.DAT provides
the first time derivatives of the coefficients for extrapolation into the
future. The 10th generation of the IGRF model (IGRF10) consists of
definitive coefficients sets for 1945 thru 2000 and prelimenary sets for
2005 and for extrapolating from 2005 to 2010.
In combination with the IGRF coefficient sets different subroutines
have been used to determine the components of the magnetic field vector
and the L-value at a given location. The NSSDC version uses the subroutines
FELDG (magnetic field vector) and SHELLG (L shell) developed by
G. Kluge at the European Space Operations Center (ESOC). His use of
inverse cartesian co- ordinates simplifies the computation. The IGRF
subroutines were developed by A. Zunde of the U.S. Geological
Survey (USGS). The program BILCAL produces tables of the geomagnetic
field strength, vector components (B-abs., B-north, B-east, B-down,
declination, inclination), equatorial/minimum field strength (B0),
dipole moment, and L-value in latitude, longitude (geodetic), altitude,
or year (decimal).
The model was realized in form of Fortran modules. Source codes of BILCAL
can be downloaded from
nssdcftp.gsfc.nasa.gov.
Tsyhanenko's RECALC module was used for calculate magnetic longitude
and latitude.
All of these programs were compiled using WATCOM FORTRAN/77 Ver.1.4 on
WindowsXP SP2 after fixing some minor bugs.
After start program will ask you name of input and output files.
If you have the file with the same name as output in the current
directory you had to delete it manually before starting of program.
Input file format:
Year Alt Lat Lon
This means year for which calculation is proceed, altitude above sea level,
geographic longitude and latitude.
Example:
1990 500 -25.36 175.5
The year had be integer number from 1945 to 2010,
altitude - integer positive number in km, latitude - number from -90 to +90 in
degrees, longitude - number from 0 to 360 in degrees.
After calculating the file will be created.
YEAR ALT LON LAT DIMO B/B0 B B0 B-NORTH B-EAST B-DOWN DIP DEC L-VALUE MLONG MLAT C
Example:
1990.0 500.0 175.50 -25.36 0.3032 3.512 0.37908 0.10793 0.23359 0.06016 -.29243 -50.5 14.4 1.422 251.89 -29.22 1
Here:
YEAR, ALT, LON, LAT are the same as in input file.
B - geomagnetic field in point of observation, Gs
B-north, B-east, B-down - components of geomagnetic vector
north, east and down (i.e.,
-Bθ,
Bφ,
-Br, Gs.)
B0 - magnetic field strength in the top of field line, that pass through
observation point.
B/B0 - relation B/B0.
L - McIlwein L parameter.
MLONG - magnetic longitude, deg
MLAT - magnetic latitude, deg
Other parameters are dipole magnetic moment of the Earth
(DIMO) and magnetic coordinates (DIP, DEC) - declination and inclination.
Download program.
