Re: [ferret_users] LSL_Lowpass filter

["William S. Kessler" <william.s.kessler@xxxxxxxx>]

The choice of 85 for the two filters does not mean the same thing. It is clear from the plot that the SPZ filter is stronger (positive-negative peaks are reduced). I suggest building intuition by trying several more values of the parameters. Can you bring the SPZ filter closer to the LSL one with smaller values of the parameter? Or vice versa? This is how to learn what these filters do and be able to judge which is appropriate for a particular problem.

BK

> On Apr 8, 2016, at 1:11 AM, saurabh rathore <rohitsrb2020@xxxxxxxxx> wrote:
> 
> hi 
> 
> from the above two replies and previous links i tried function L=@SPZ:85 (12*7=84 but spz works for odd number) and the results are more or less similar. here red line is for L=@spz:85 and black line is the LSL_Lowpass( A, 84, 85).
> 
> regards
> 
> On Thu, Apr 7, 2016 at 11:55 PM, Edward Cokelet - NOAA Federal <edward.d.cokelet@xxxxxxxx> wrote:
> If you search on “frequency response” in the ferret e-mail archives (http://ferret.pmel.noaa.gov/static/Ferret_search/ferret_mail_archives.html), you’ll find a contribution from me 
> (http://www.pmel.noaa.gov/maillists/tmap/ferret_users/fu_2015/msg00055.html) on 17 Feb 2015 about a ferret script that gives an example of the frequency response of the LSL_Lowpass filter.  As Billy Kessler pointed out, you will always lose some points off both ends of the filtered data.  If the filter is symmetric and 2N+1 points wide, then the filtered data will have missing values at the first and last N points.  
> 
> I attach a slightly clearer version of that LSL Lowpass frequency response script here:
> 
> 
> 
> 
> ------------------------------------------------------------------------------------------
> Edward D. (Ned) Cokelet, Ph.D. Oceanographer
> NOAA/PMEL                         off:  (206) 526-6820
> 7600 Sand Point Way NE     fax: (206) 526-6485
> Seattle, WA 98115-6349
> 
> Edward.D.Cokelet@xxxxxxxx
> 
> The contents of this message are mine personally and do not necessarily reflect any position of the Government or the National Oceanic and Atmospheric Administration.
> 
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> -- 
> 
> 
> REGARDS
> 
> Saurabh Rathore
> M.Tech (Earth System Sciences & Technology)
> Centre For Oceans, Rivers, Atmosphere & Land Science Technology
> Indian Institute Of Technology, Kharagpur
> contact :- 91- 8345984434
> <filter_lsl_spz.png>