Re: Should I standardize the time series before using "specx_anal" ?

>> I found that the spectrum plot will be changed
>> greatly if I standardize the time series before
>> using "specx_anal".
>>
>> I am a little puzzled on it. Is it necessary to
>> do a standardization at first when we analyze the spectrum ?
>>
>> ( I analyze the 102-yrs precipitation datas , all data ,
>> script and plots have been uploaded to ftp://cgd.ucar.edu/incoming/ )
>-------------
>
>Standardization normalizes the data [variance=1].
>
>The point of spectral analysis is to look at which frequency
>bands have the most variance and are they significant
>either physically or statistically.
>
>Don't normalize before doing spectral analysis.

=====
All ...

[1] I apologize for the above response.
    I did not look at the script before I replied!
    More important, I did not think before I replied :-(
        
[2] The spectral pattern should be the same
    whether the data are normalized or not.
    Of course, the magnitudes will be different.
    
[3] Before responding this time, I decided to
    look at the script that was sent. :-)
    
The original code had:

    prcp = asciiread("foo.dat",(/102,8/),"float")
    prcp = dim_standardize(prcp,1)
    
As noted in the "dim_standardize" documentation the
*rightmost dimension* is being operated upon.
      (like all the dim_* functions)
      
Based upon the script the left dimension represents "time"
and the right "stations"

Does anyone see the problem?!?!

Answer: the dimensions must be reordered to get the standardized
        time series at each station. The following is suggested
        
   PRCP = asciiread("foo.dat",(/102,8/),"float")
   PRCP!0 = "time"
   PRCP!1 = "station"
   
   prcp = PRCP(station|:,time|:) ; make time the rightmost dimension
   prcp = dim_standardize(prcp,1) ; for each station
                                        ; standardize over time
 
D
D

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Received on Thu Feb 08 2007 - 11:50:13 MST