Re: Deseasonalization and detrending of Keeling curve
- From: David Winsemius <doe_snot@xxxxxxxxxxx>
- Date: Sat, 20 Jan 2007 21:07:05 -0600
"Pekka Jarvela" <pekkajarvela@xxxxxxxxx> wrote in
news:1169326747.707212.147920@xxxxxxxxxxxxxxxxxxxxxxxxxxxx:
CO2 concentrations in atmosphere measured at Mauna Loa in Hawaii are
known as Keeling curve, http://en.wikipedia.org/wiki/Keeling_curve You
can get the update date from
http://scrippsco2.ucsd.edu/data/in_situ_co2/mlo_in_situ_record.txt In
this page it is said that
"The "detrended" data is seasonally adjusted by removing a 4-harmonic
fit with a linear gain factor. The "fit" is based on a stiff spline
plus 4-harmonic functions with linear gain."
1. Is detrending fitting a line y = ax + b to data and then subtracting
this line from data?
2. What does "removing a 4-harmonic fit with a linear gain factor"
mean? Has this something to do with Fourier analysis?
http://repositories.cdlib.org/cgi/viewcontent.cgi?article=1190&context=sio
"The number of harmonics refers to a portion of the fitting function which
involves sinusoidal terms with a fundamental period of one year plus higher
order Fourier components. Thus, 2 harmonics indicates that terms with periods
of 1 year and 6 months were fit, 4 harmonics indicates additional terms with
periods of 4 and 3 months."
See also
http://repositories.cdlib.org/cgi/viewcontent.cgi?article=1110&context=sio
.
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