[CIG-SEISMO] Noise simulation in SPECFEM2D

[Yingzi Ying]

Hi Yang,

I checked the code "noise_tomography.f90" again and attached a snip bellow
-------------------------------------------------------
   elseif( time_function_type == 4 ) then
     !reproduce time function from Figure 2a of Tromp et al. 2010
     do it = 1,NSTEP
       t = it*deltat
       time_function_noise(it) = factor_noise * &
        4.*aval**2. * (3. - 12.*aval*(t-t0)**2. + 
4.*aval**2.*(t-t0)**4.) * &
        exp(-aval*(t-t0)**2.)
     enddo

-------------------------------------------------------

Is there should be a "-" sign before "factor_noise"? If I did this, the 
result will be just corrected, even the length of cross-correlation is 
still in controversial.

Best,
Yingzi
On 01/28/2013 08:54 PM, Yang Luo wrote:
> Hi Jeroen & Yingzi,
> I didn't implement the 2D version, which was actually done by Ryan
> (cc-ed) based on the 3D code we have already had.
> But I just checked the 2D code again and ran the example Yingzi
> mentioned, all looks good to me.
> The code I have may not be current, since I cannot use svn to get the
> latest version.
> But since the older version I have works, I assume the latest one should
> work as well.
> Yingzi, please see my following two cents, and make sure that you didn't
> misunderstand what you have already obtained from your tests.
> 1. the positive branch --- it refers to the second half (i.e., 60 to 120
> s for the example) of the seismograms you obtained (not for t>0 in the
> simulation).
> In other words, our simulation actually should start from t=-60s, but to
> avoid introducing this complexity, the time axis has been shifted.
> Given this into consideration, I think what you saw (i.e., two envelops)
> in your seismograms is correct.
> You just missed the point that the time from the simulation (almost
> always positive) is not the cross-correlation time (could be negative).
> Tromp et. al. (2010) provides step-by-step figures, which I think you
> might not fully understand yet.
> 2. the time_function_type --- you are right, the default should be
> changed to the one that reads in the file S_squares.
> But for benchmarking purposes, it is fine to put the one we have used in
> our paper.
> (Ryan, could you please fix that? just provide a default S_squres file
> there using the time_function you hard coded).
> 3. nu_master --- it refers to the noise direction, which is trivial in 2D.
> Yingzi, should you still be confused or claim that what you saw is
> totally different from the paper,
> please provide a picture of what you saw.
> Thanks,
> Yang
>
>
> On Mon, Jan 28, 2013 at 11:45 AM, Jeroen Tromp <jtromp at princeton.edu
> <mailto:jtromp at princeton.edu>> wrote:
>
>     Hi Yang:
>
>     A question for you.
>
>     Best regards,
>
>     Jeroen
>
>
>     Begin forwarded message:
>
>>     *From:* Yingzi Ying <yingzi.ying at me.com <mailto:yingzi.ying at me.com>>
>>     *Date:* January 28, 2013, 11:18:00 PST
>>     *To:* "cig-seismo at geodynamics.org
>>     <mailto:cig-seismo at geodynamics.org>" <cig-seismo at geodynamics.org
>>     <mailto:cig-seismo at geodynamics.org>>
>>     *Subject:* *[CIG-SEISMO] Noise simulation in SPECFEM2D*
>>     *Reply-To:* <cig-seismo at geodynamics.org
>>     <mailto:cig-seismo at geodynamics.org>>
>>
>>     Dear Tromp, Dimitri and all,
>>
>>     I am interested in noise simulation with SPECFEM2D(V7.0.0) to get
>>     ensemble cross-correlation. I tried to reproduce the result in
>>     fig. 2(a)
>>     in Tromp's paper "Noise cross-correlation sensitivity kernels" by
>>     executing ./process.sh in EXAMPLES/noise_uniform/.
>>
>>     My calculated interferogram after step 2 has two envelopes in the
>>     positive branch, and their positions are unconcerned with the time
>>     delay
>>     between two stations. This is totally different with the Tromp's
>>     result.
>>
>>     I checked the source code "noise_tomography.f90" and found the value
>>     "time_function_type" is fixed to "4", which means the variable
>>     "time_function_type" in "DATA/SOURCE" will not take action and the
>>     "DATA/NOISE_TOMOGRAPHY/S_squared" will not be read. Furthermore,
>>     there
>>     is no "nu_master" in SPECFEM2D, which exists in 3D version.
>>
>>     I don't know what goes wrong, and what I should do to get a correct
>>     ensemble interferogram. Anyone who knows please kindly give me a hint.
>>
>>     Thanks in advance.
>>
>>     Best,
>>     Yingzi
>>     _______________________________________________
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>
>