[ncl-talk] The question about the complex demodulation

[Dennis Shea]

If the low-pass filtering (Lanczos) and smoothing (weighted running
average) don't explain the differences... I do not know.
I do not have Bloomfield's 1976 book readily available. That used the
1700-1960 sunspot numbers. As I recall, NCL's plots were 'identical' to
those in the 1976 book.
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http://www.ncl.ucar.edu/Applications/spec.shtml

Data Analysis: Spectral analysis, Complex Demodulation

The 1st complex demodulation example uses the 1700-1960 sunspots
http://www.ncl.ucar.edu/Applications/Scripts/demod_cmplx_1.ncl
----

The 'demod_cmplx' function can be seen at:

%> less  $NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl

Basically, it is a translation (fortran-77  ===> NCL) of Bloomfield's 1976
f77 subroutine.






On Tue, Dec 12, 2017 at 4:03 AM, Nai Suan <shif422 at gmail.com> wrote:

> Dear colleague,
>         I have a question about how to explain the phase of the complex
> demodulation. I found that the phases of the sunspot in the figures 7.9 and
> 7.11 (see the attachment) in Bloomfield (2000)’s book (chapter 7 complex
> demodulation) were totally different with the ‘demod_cmplx_1_lg.png (see
> the attachment)’. Which is right? I believe the original sunspots in two
> examples are same and the different low-pass filter methods can not be used
> to explain this difference. How to explain the difference?
>         Hope to hear your answer.
>         All the best,
> Frank
>
>
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> >
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