From: Carson Farmer <cfarmer_at_uvic.ca>

Date: Mon, 28 Jan 2008 15:10:38 -0800

*> In general the actual frequency of the curve will indeed be close to
*

*> 1/(1 year). However, because I intend to perform this analysis on many
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> regions, this will not always be the case. This is perhaps an

> acceptable assumption however...

*> What I am really trying to do is fit a relatively smooth line to my
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*> data which will preferentially weight the larger values. This method
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*> needs to be able to fit through data gaps however, which is why I was
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*> originally looking to fit sinusoids. A jpg of a single year of the
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*> data is available here:
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*> <**http://www.geog.uvic.ca/spar/carson/snowDepth.jpg> to give you an
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> idea of the shape of my curve.

> Thank you again for your help,

> Carson

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Mon 28 Jan 2008 - 23:14:04 GMT

Date: Mon, 28 Jan 2008 15:10:38 -0800

>> >> On 26/01/2008, at 10:54 AM, Carson Farmer wrote: >> >>> Dear List, >>> >>> I am attempting to perform a harmonic analysis on a time series of snow >>> depth, in which the annual curve is essentially asymmetric (i.e. snow >>> accumulates slowly over time, and the subsequent melt occurs relatively >>> rapidly). I am trying to fit a curve to the data, however, the actual >>> frequency is unknown.

> regions, this will not always be the case. This is perhaps an

> acceptable assumption however...

>> Obviously there is something I am not understanding here. >> I would have thought that the ``actual frequency'' would >> be 1/(1 year) (period = 1 year) --- modulo the fact that >> the length of the year is constantly changing a tiny bit. >> (But I would've thought that this would have no practical >> impact in respect of any observed series.) >>

> My sampling interval is daily.

>> What is your sampling interval, BTW? Day? Week? Month? >>> I have been trying to follow the methods in Peter >>> Bloomfields text "Fourier Analysis of Time Series", but am having >>> trouble implementing this in R.

> Yes it certainly would.

>> Note that even though the ``actual frequency'' is (???) 1/(1 year), >> the representation of the mean function in terms of sinusoids >> will involve in theory infinitely many terms/frequencies since >> the mean function is clearly (!) not a sinusoid. >> >>> Does anyone have any suggestions, or perhaps directions on how this >>> might be done properly? Am I using the right methods for fitting an >>> asymmetric curve?

> idea of the shape of my curve.

> Thank you again for your help,

>

> Carson

>> >> I would have to know more about what you are *really* trying >> to do, and what the data are like, before I could make any >> useful suggestions. Many modelling issues could come into >> play, and many modelling strategies are potentially applicable. >> >> cheers, >> >> Rolf Turner >> ______________________________________________R-help_at_r-project.org mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Mon 28 Jan 2008 - 23:14:04 GMT

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