Please Let me know how to apply cloud mask and color palettes to improve results. Its Mexico City data related to webinar by A. Papageorgou HAZA03
Regards
please have a look at this discussion on the masking of areas of low coherence:
I did it after TC and not tried the way you have mentioned Abraun.
looks good!
Not every value in the product can be trusted. Mask out low coherence areas to have a more reliable result.
That requires the coherence band to be included in the final product, so you have to select it in the Terrain Correction step.
Have a look here: Subsidence map in 3d view
Good job! You got nice results!
Just pointing out that taking subsidence values out of unwrapped DInSAR results (after applying TopoPhaseRemoval), you must remember the remaining phase contributions of the phase you had filtered (with Goldstein) and unwrapped (deformation+atmosphere+noise).
Surely you still has atmospheric artifacts in the interferometric phase as well as other noise sources that you could remove using more advance interferometric techniques such as PSI, SBAS …
In the specific case of Mexico city, where the deformation is such high (in the order of 2.5cm/month) that other contributions could be not considered*, but only in such cases of high deformation.
Atmosphere still could produce errors of such magnitude, but limiting the area of interest to few kilometers you could limit the atmosphere differences among the image.
Thanks Abraun and Mdelgado.
I will keep on advancing as per your comments and update.
I had removed low coherence upto 0.4.
May i remove upto 0.6?
also in your exported image? It doesn’t seem to have any masked areas…
Dear ABraun plz tell where could be a mistake?
Can i mask out area color (light blue) from final product?
Is it seems coh thresholding is not proper?
PSI/SBAS could not be implemented this time. See it later.
Do you mean i should take a subset and then proceed?
if you want to exclude zero displacement areas, formulate your valid pixel expression as follows:
displacement_VV > -0.01 AND displacement_VV < 0.01
Play around with the thresholds to find out the perfect ones. Optionally, include coherence:
displacement_VV > -0.01 AND displacement_VV < 0.01 AND coherence > 0.6
This, however, requires the coherence to be in the same product.
I have found Subsidence with 0.6 coh threshold. Showing -7.6 cm subsidence and 2.8cm uplift.
Please justify uplift? is it due to some errors?
Regards
ASVirk
One another area results are here. DInSAR taking two images with 36 days temporal difference.
Shown subsidence and uplift.
Please help me to understand the phenomenon.
Subsidence is at uphill and uplift if in the bottom of hills. Is it due to the fact that snow from top has melted and accumulated at the bottom? Snow starts melting from April to August each year. (Images taken in the month of may and June)
the extreme values do not matter the most. It is important that the general pattern of your displacement makes sense. The mimimum and maximum displacement values often are produced by atmospheric influences or unwrapping errors.
As for your second example: Is it a coherent change that is expected? That means did the surfaces change their properties in any way (besides their elevation)?
I don’t know any of your study areas and cannot judge if the results make sense but your second example looks like there is a ramp in your data between the eastern and western part. It is always good to look at all steps of the processing. Does the interferogram look alright?
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Surface change due to snow accumulation or melting only.
Landslide was there on date 28th June.
I will be covering this date in next processing.
Plz see Interferogram
Both snow melt and landslides are primarily non-coherent processe, thant means the surfaces change their backscatter characteristics and the pixel information is out of phase. This makes them unsuitable for differential interferometry.
Have a look at mengdahls explanations here: How can we calculate the volume of displaced material with displacement band(displacement_VV)? (this post and two below).
Sometimes, the fringes you see in your interferogram are heavily affected by atmosphere. I cannot tell what is the case in your study because I don’t know the area and the dynamics.
Have a look at this example, where the inteferogram is compared to the atmospheric phase screen (APS), an estimation of the influcence of atmosphere on your data.
What looks like nice fringes on the left turns out to be predominantly caused by atmospheric disturbance (right). It is therefore often a good idea to calculate interferograms of multiple image pairs to see which patterns persist and which are random.
Where should we fix reference point (A pixel point assuming no deformation at it have taken place) to subtracting its calculated displacement value from all displacement values.
Coherence should be high or low for this point?
I honest cannot tell. These are relative displacement values and one has to consider the nature of the study area to select one.
Have a look at the displacement pattern and select a point where there is not much dynamic.
But high coherence is also a good thing to look for.