[ncl-talk] The question about the complex demodulation

[Nai Suan]

Dear Dennis Shea,
	I found a same mistake in two documents Kessler: U. Washington: Complex Demodulation and PMEL: Complex Demodulation. The first formula should be conected by a ‘plus’ sign not ’minus’ sign. 
	All the best,
Feng



> On Dec 13, 2017, at 10:02 AM, Nai Suan <shif422 at gmail.com> wrote:
> 
> Dear Dennis Shea,
> 	Thank you for your reply.
> 	If I am right, the phases of the 1700-1960 sunspot numbers has a unique solution. This means Bloomfield’s 2000 (Second Edition) is wrong or the 1st complex demodulation example in NCL is wrong. I have no idea for another option.
> 	You mentioned NCL example was translated from Bloomfield’s subroutine. Is there any possible reason that the translation has some problems?
> 	Anyway, if you are interested, I can send Bloomfield’s 2000 book to you.
> 	All the best,
> Frank
> 
> 
>> On Dec 13, 2017, at 12:15 AM, Dennis Shea <shea at ucar.edu> wrote:
>> 
>> 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. 
>> ----
>> 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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