How I can remove orbital error from ROI-PAC result?

2015 8 18
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更新时间：2015 8 26
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Hello,
I have been using ROI-PAC (Radar processing software)to process my SAR data. I produced unwrapped geocoded images. However I still need to remove orbital fringes which causes some problem for analyzing deformation.
I would be pleased if anyone knows how to remove orbital fringes using Matlab.
Thanks in advance.
Regards, Ruken

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Brian Neiswander
Brian Neiswander 2015-8-20

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I understand that you would like to remove orbital fringes from unwrapped SAR data. This really depends on the nature of the deformations that you are trying to analyze. Orbital phase error can usually be characterized by its long spatial wavelength. If this wavelength is distinct from the deformations, then it should be relatively easy to remove the orbital error using a linear detrending or high-pass filtering scheme. Note that whatever technique you use, there will always be some residual error.
A more complicated approach is to use the orbital phase information to correct the satellite trajectories, which can then be used to eliminate the error.
You may also want to check with the ROI-PAC team to see if they have any further suggestions.

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Ruken
Ruken 2015-8-21
Hi Brian,
Thanks a lot. The thing is I am not very familiar with Matlab. I am using it some simple application. Do you know any scripts for linear detrending or high-pass filtering scheme?
I would be pleased if you help me. Ruken
Brian Neiswander
Brian Neiswander 2015-8-21
Hi Ruken,
You can use the "detrend" function to linearly detrend your data, as shown below:
>> y = detrend(x); %x is a MxN array
Using a high-pass filter on 2-D data is a little more complicated. This can be done using the "imfilter" function or "filter2" function. You can find a simple high-pass filter example in this MATLAB Answers post:
http://www.mathworks.com/matlabcentral/answers/26155-high-pass-filter-implement-on-a-image
You can follow the links below for more information on the "detrend", "imfilter", and "filter2" functions:
http://www.mathworks.com/help/matlab/ref/detrend.html
http://www.mathworks.com/help/images/ref/imfilter.html
http://www.mathworks.com/help/matlab/ref/filter2.html
Hope this helps.
-Brian
Ruken
Ruken 2015-8-25
Hi Brain,
Thank you very much. I used below detrend function
>> y = detrend(t,'constant');
However, I have not seen any changes. I tried to use below imfilter function
a = fspecial('unsharp'); b = imfilter(t, H);
Not any changes as well.
I was just wondering am I using correctly those function. Would be happy if you just give me a comment about it.
Thanks in advance.
Ruken
Ruken
Ruken 2015-8-26
Hi Brain,
Thanks for your help.
I found a way to do it. However I guess it is not very effective to use detrend.
Ruken

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