oce (version 0.2-1)

magneticDeclination: Earth magneticDeclination

Description

Earth magneticDeclination

Usage

magneticDeclination(lat, lon, date)

Arguments

lat

latitude in degrees north, a number, vector, or matrix.

lon

longitude in degrees east (negative for degrees west). The dimensions must conform to lat.

date

decimal year, either a single number or a vector or matrix whose dimensions conform to those of lat.)

Value

• Magnetic declination.

concept

tide

Details

Implements the International geomagnetic reference field, based on a reworked version of a Fortran program downloaded from a NOAA website. The code seems to have been written by Susan Macmillon of the British Geological Survey. Comments in the code indicate that it employs coefficients agreed to in December 2009 by the IAGA Working Group V-MOD. The code also suggests that the valid time interval is 1900.0 to 2015.0, with values up to 2020 having reduced accuracy. And, finally, values for dates 1945 to 2005.0 are said to be "non-definitative", with other values in the range being declared "definitative".

References

http://www.ngdc.noaa.gov/IAGA/vmod/igrf.html

Examples

library(oce)
lat <- seq(47.80, 48.00, length.out=30)
lon <- seq(-69.9, -69.6, length.out=30)
lonm <- matrix(rep(lon,length(lat)),ncol=length(lat),byrow=TRUE)
latm <- matrix(rep(lat,length(lon)),nrow=length(lon),byrow=FALSE)
dec <- magneticDeclination(latm, lonm, 2008 + 7 / 12)
data(coastlineSLE)
plot(coastlineSLE)
contour(x=lon, y=lat, z=dec, add=TRUE)