Using the magnetic field calculator

Calculating a magnetic field To calculate a magnetic field, you simply fill out the "Calculate Magnetic Field" form under the "Magnetic Field" tab of the Magnetic Field Calculators page, then click "Calculate" at the bottom. Below is an explanation of the each of the sections contained within the calculator form.

Location

Longitude and Latitude: Entered in either "decimal degrees" or "degrees minutes and seconds (space separated integers)"
Elevation: Elevation is especially important when computing the magnetic field at aircraft or higher altitudes. If you are unsure of your elevation, and are interested in a location on the surface of Earth, the default of 0 is sufficient.

If you do not know the longitude and latitude of the location you are trying to use, try looking it up using the "Lookup location" form on the right-hand side of the calculator, which will populate the longitude and latitude values in the calculator form for you.

If the "Location lookup" can't find your location, you can try to look up your location by going to the "U.S. Gazetteer" for locations within the United States, or the Getty Thesaurus for locations outside of the United States. If you lookup your location using one of these links, please enter the latitude and longitude you find directly into the calculator form on the left. If you are entering the location in degrees, minutes, and seconds, please enter the values separated by a single space. Remember, there are 60 seconds in a minute and 60 minutes in a degree, therefore 35° 30' 0" is equivalent to 35.500. Do not enter the N, S, E, or W designation in the box! The box should be a positive value and the hemisphere should be designated by selecting a value from the choices to the right of the text field. N stands for northern hemisphere latitude, S for southern hemisphere latitude, W for western hemisphere longitude, and E for eastern hemisphere longitude. The USA is (mostly) located in the northern (N) and western (W) hemispheres, which have been pre-populated for you. Latitude ranges from 90° south (south pole) to 90° north (north pole) with 0° meaning the equator. Longitude ranges from 0° (Greenwich, England) eastward through 90° East (Bangladesh) to 180° and westward across the Atlantic from 90° West (Jackson, MI) to 180°.

Model

Model: The model you wish to use for calculating the magnetic field.

The magnetic field calculator supports two different models for calculating the magnetic field. The first of the two is the IGRF11, which is produced by the voluntary research of the scientific community under the banner of the International Association of Geomagnetism and Aeronomy (IAGA). The IGRF is retrospectively updated and the latest update, and is valid for the years 1900.0 - 2015.0. For more information on the IGRF11 model, Please go here.

The second model is the WMM 2010, which is produced for the US and UK defense agencies with guaranteed quality, user support, and updates. The WMM is a predictive-only model and is valid for the current epoch (2010.0 to 2015.0). For more information on the WMM model, Please go here.

The IGRF and WMM are both estimated from the most recent data and are of comparable quality.

Date range

Start Date: The year you wish the magnetic field calculations to begin with. (Defaults to the current date).

End Date: The year you wish the magnetic field calculations to end with. (Defaults to the current date).

Step size: The interval that you would like your date range to be calculated with. For example, if you select 2010 for your start date, and 2014 for your end date, and a step size of 2, your will get declination values for 2010, 2012, 2014 (every 2 years).

Result

Result format: The format you wish to view the results in. This allows you to view the results in a popup window (HTML), XML, or as comma separated values (CSV).

Using the programmatic interface

The calculator provides an easy way for you to get results in HTML, XML, or CSV programmatically. To use the programmatic interface, you just have to url-encode the form parameters into a GET request including the result format you want.

The following is a list of parameters and the base url needed to perform a declination calculation programmatically.

BASE URL: http://www.ngdc.noaa.gov/geomag-web/calculators/calculateIgrfwmm

PARAMETERS

Parameter	Required	Default	Description
lat1	yes		decimal degrees or degrees minutes seconds: -90.0 to 90.0
lon1	yes		decimal degrees or degrees minutes seconds: -180.0 to 180.0
elevation		0.0	elevation of calculation location: -10 - 600 km
elevationUnits		K	units of elevation parameter: 'K', 'M', or 'F'
model	yes		which magnetic reference model to use: 'WMM' or 'IGRF'
startYear		current year	start year of calculation interval: 1900 - 2014 for IGRF model, 2010-2014 for WMM model
startMonth		current month	start month of calculation interval: 1 - 12
startDay		current day	start day of calculation interval: 1 - 31
endYear		current year	end year of calculation interval: 1900 - 2014 for IGRF model, 2010-2014 for WMM model
endMonth		current month	end month of calculation interval: 1 - 12
endDay		current day	end day of calculation interval: 1 - 31
dateStepSize		1.0	size of steps through calculation interval in decimal years
resultFormat		html	format of calculation results: 'html', 'csv', or 'xml'

EXAMPLE:

An XML document with magnetic field values in Boulder once a year since today's date in 2010 to the present using the World Magnetic Model
http://www.ngdc.noaa.gov/geomag-web/calculators/calculateIgrfwmm?lat1=40&lon1=-105.25&model=WMM&startYear=2010&resultFormat=xml

Interpreting the results

Declination: Declination is the angle of difference between true North and magnetic North. For instance, if the declination at a certain point were 10° W, then a compass at that location pointing north (magnetic) would actually align 10° W of true North. True North would be 10° E relative to the magnetic North direction given by the compass. Declination varies with location and slowly changes in time.

Inclination: At a given location, the Inclination is the angle between the magnetic field vector and the horizontal plane (the plane is tangent to the surface of the Earth at that point). The inclination is positive when the magnetic field points downward into the earth and negative when it points upward.

Horizontal Intensity: The horizontal intensity is the intensity of the component of the magnetic field is tangent to the Earth surface at a given point.

North Component: The North component is the portion of the magnetic field that is directed horizontally northward. A southward directed field would have a negative value for the North component.

East Component: The East component is the portion of the magnetic field that is directed horizontally eastward. A westward directed magnetic field has a negative value for the East component.

Vertical Component: The vertical component is the portion of the magnetic field that is directed perpendicular to the Earth's surface at a given location. Down is measured as positive and up as negative.

Total Field: The total field is the intensity (or strength) of the entire magnetic field at a given location. Geometrically, it is the length of the magnetic field vector.

Change/year: The total amount each component has changed between the calculated year, and the year before it.

*Accuracies for the angular components (Declination and Inclination) are reported in degrees and minutes of arc and are generally within 30 minutes (0.5 degrees) of arc.

*Accuracies for the force components (Horizontal, North, East, Vertical, and Total force) are generally within 100 to 250 nanotesla.

*Solar disturbances can cause significant differences between the estimated and actual field values. You can check the current solar conditions from NOAA's Space Environment Center . For more information on Earth's magnetic field parameters, please visit our Frequently Asked Questions section.

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