I am working on sentinel 1-A SLC product to map surface deformation

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hi
I do all necessary procedures and I got convincing DInSAR result . But i struggle on the displacement map. I use snaphu1.4.2 for phase unwrapping

I explore all related answers to my question, I saw this one , However i have some confusion even now.
Where i got wavelength in mm?
In which image i can do coherence mask ?
In which image i do subtraction (Subtract 45 from your image)? What about the negative values?

Here is the answer I got on step forum page

  1. (Unw_Phase * wavelength in mm) / (-4 * PI * cos(rad(incident_angle)))
    This gives you the relative change between two satellite images in milimeters
    Source: http://www.esa.int/esapub/tm/tm19/TM-19_ptA.pdf , chapter 2.3.
  2. Crop out areas with a low coherence (Layer properties > valid pixel expression, for example coh_HH_11Feb2008_04Mar2008 > 0.6 ).
  3. Select a point where you assume no change and read the value. Let’s say its 45 cm
  4. Subtract 45 from your image in order to have zero values at those areas with no change. The remaining variation should be due to subsidence between two overpasses
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