# Help: Magnetic Field Component Grid Calculator

Calculating a magnetic field component grid Use the "Calculate Magnetic Field Component Grid" form under the "Magnetic Field Grid" 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
• Max Longitude: The eastern most longitude value. Entered in either "decimal degrees" or "degrees minutes and seconds (space separated integers)"
• Min Longitude: The western most longitude value. Entered in either "decimal degrees" or "degrees minutes and seconds (space separated integers)"
• Lon Step Size: The interval that you would like your longitude range to be calculated with. For example, if you enter 100 W for your min longitude, and 180 W for your max longitude, and a step size of 10, your will get results for longitude values 100 W, 110 W, 120 W, 130 W 140 W, 150 W, 160 W, 170 W, and 180 W.
• Max Latitude: The northern most latitude value. Entered in either "decimal degrees" or "degrees minutes and seconds (space separated integers)"
• Min Latitude: The southern most latitude value. Entered in either "decimal degrees" or "degrees minutes and seconds (space separated integers)"
• Lat Step Size: The interval that you would like your latitude range to be calculated with. For example, if you enter 20 N for your min latitude, and 90 N for your max latitude, and a step size of 10, your will get results for latitude values 20 N, 30 N, 40 N, 50 N 60 N, 70 N, 80 N, and 90 N.
• 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.

GPS: The height above the World Geodetic System (WGS-84) ellipsoid.

MSL: Approximate height above mean sea level. More precisely it is height above the surface of the geoid defined by the Earth Gravitational Model 1996 (EGM96).

• NOTE: The grid calculator allows for calculation of magnetic field values for an area or a point. In order to calculate a grid of components for an area, you fill out min and max longitude and min and max latitude values in order to define a bounding box for the area of interest. To get the components for a single point, the min and max longitude values should be the same, and the min and max latitude values should be the same. For example:

To input an area:

Max longitude = 85 1 39.6192 W
Min longitude = 125 1 39.6192 W
Lon Step Size = 1.0
Max latitude = 60 3 3.7836 N
Min latitude = 20 3 3.7836 N
Lat Step Size = 1.0

To input a point:

Max longitude = 105 1 39.6192 W
Min longitude = 105 1 39.6192 W
Lon Step Size = 1.0
Max latitude = 40 3 3.7836 N
Min latitude = 40 3 3.7836 N
Lat Step Size = 1.0

If you do not know the longitude and latitude, use Lookup Latitude / Longitude in the box to the right of the calculator, which will populate the longitude and latitude values in the calculator form for you.

If Lookup Latitude / Longitude can't find your location, search for an address at USGS Earth Explorer.

Enter the latitude and longitude into the calculator form on the left. If the location is 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°.

Component
• Magnetic component: The component of the magnetic field you wish to calculate the grid for.
Model
• Model: The model you wish to use for calculating the magnetic field.

The magnetic field calculator supports two models. The International Geomagnetic Reference Field (IGRF) 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 valid for the years 1590-2014. IGRF model: http://www.ngdc.noaa.gov/IAGA/vmod/igrf.html.

The World Magnetic Model (WMM) is produced for the U.S. and U.K. defense agencies with guaranteed quality, user support, and updates. The WMM is a predictive-only model and is valid for the current epoch, 2014-2019. WMM model details: http://ngdc.noaa.gov/geomag/WMM.

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 Format
• The format you wish to view the results in. This allows you to view the results in a separate browser 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 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.

A maximum of 50 connections/second from all the users is allowed at any time. If this is exceeded, the back-end calculator stops taking requests for 10 seconds. Bulk calculations should be requested serially and not in parallel. If the requests start returning with errors then your script should go to sleep for 5-10 minutes before trying the next request.

EXAMPLE:

An XML document with a grid of inclination values near Boulder today with data points every tenth of a degree in latitude and longitude:
http://www.ngdc.noaa.gov/geomag-web/calculators/calculateIgrfgrid?lat1=39.8&lat2=40.3&lon1=-105.5&lon2=-105&latStepSize=0.1&lonStepSize=0.1&magneticComponent=i BASE URL: http://www.ngdc.noaa.gov/geomag-web/calculators/calculateIgrfgrid

PARAMETERS

Parameter Required Default Description
lat1yesnorthern-most latitude bound in decimal degrees or degrees minutes seconds: -90.0 to 90.0
lat2yessouthern-most latitude bound in decimal degrees or degrees minutes seconds: -90.0 to 90.0
latStepSize1.0size of steps through latitude interval in degrees
lon1yeswestern-most longitude bound in decimal degrees or degrees minutes seconds: -180.0 to 180.0
lon2yeseastern-most longitude bound in decimal degrees or degrees minutes seconds: -180.0 to 180.0
lonStepSize1.0size of steps through longitude interval in degrees
elevation0.0elevation of the location: > -10 km
elevationUnitsKunits of elevation parameter: 'K', 'M', or 'F'
coordinateSystemM'D' (GPS) or 'M' (Mean Sea Level)
magneticComponentyesmagnetic component to include in result grid, one of:
d = Declination
i = Inclination
x = North component
y = East component
z = Vertical intensity
h = Horizontal intensity
f = Total intensity
modelWMMwhich magnetic reference model to use: 'WMM' or 'IGRF'
startYearcurrent yearstart year of calculation interval: WMM:2014-2019, IGRF:1590-2014
startMonthcurrent monthstart month of calculation interval: 1 - 12
startDaycurrent daystart day of calculation interval: 1 - 31
endYearcurrent yearend year of calculation interval: WMM:2014-2019, IGRF:1590-2014
endMonthcurrent monthend month of calculation interval: 1 - 12
endDaycurrent dayend day of calculation interval: 1 - 31
dateStepSize1.0size of steps through calculation interval in decimal years
resultFormatxmlformat of calculation results: 'xml' or 'csv'
Interpreting Results
• Declination: 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 intensity of the component of the magnetic field is tangent to the Earth surface at a given point.

North Component: 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 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 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 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.

Uncertainty: The one standard deviation difference between a hypothetical measurement and the calculator result.

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

*Accuracies for the force components (Horizontal - H, North - X, East - Y, Vertical - Z, and Total force - F) 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 Weather Prediction Center. More on Earth's magnetic field parameters: Frequently Asked Questions.
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