(45) Trend modeling

In this example show how the module trend1d is used to fit the CO2 data set collected from the top of Mauna Loa. This yields the famous Keeling curve.

#!/usr/bin/env bash
#               GMT EXAMPLE 45
#
# Purpose:      Illustrate use of trend1d mixed models
# GMT modules:  text, plot, trend1d
# Unix progs:   rm
#

gmt begin ex45
	gmt set FONT_HEADING 24p
	gmt subplot begin 4x1 -Fs6i/1.9i -R1958/2016/310/410 -Bxaf -Byaf+u" ppm" -BWSne+gazure1 -T"The Keeling Curve [CO@-2@- at Mauna Loa]"

		# Basic LS line y = a + bx
		gmt subplot set 3
		gmt trend1d -Fxm @MaunaLoa_CO2.txt -Np1 > model.txt
		gmt plot -Sc0.05c -Gred @MaunaLoa_CO2.txt
		gmt plot -W0.5p,blue model.txt
		gmt text -F+f12p+cTL+t"m@-2@-(t) = a + b\264t" -Dj0.1i -Glightyellow

		# Basic LS line y = a + bx + cx^2
		gmt subplot set 2
		gmt trend1d -Fxm @MaunaLoa_CO2.txt -Np2 > model.txt
		gmt plot -Sc0.05c -Gred @MaunaLoa_CO2.txt
		gmt plot -W0.5p,blue model.txt
		gmt text -F+f12p+cTL+t"m@-3@-(t) = a + b\264t + c\264t@+2@+" -Dj0.1i -Glightyellow

		# Basic LS line y = a + bx + cx^2 + seasonal change
		gmt subplot set 1
		gmt trend1d -Fxmr @MaunaLoa_CO2.txt -Np2,f1+o1958+l1 > model.txt
		gmt plot -Sc0.05c -Gred @MaunaLoa_CO2.txt
		gmt plot -W0.25p,blue model.txt
		gmt text -F+f12p+cTL+t"m@-5@-(t) = a + b\264t + c\264t@+2@+ + d\264cos(2@~p@~t) + e\264sin(2@~p@~t)" -Dj0.1i -Glightyellow

		# Plot residuals of last model
		gmt subplot set 0
		gmt plot -R1958/2016/-4/4 -Byafg10+u" ppm" -Sc0.05c -Gred model.txt -i0,2
		gmt text -F+f12p+cTL+t"@~e@~(t) = y(t) - m@-5@-(t)" -Dj0.1i -Glightyellow

	gmt subplot end
	rm -f model.txt
gmt end show

Trend Modeling.