Thank you for the idea. What I did after obtaining a displacement product after applying terrain corrections was this:
In my coherence band where I also applied terrain correction, I masked the pixels with coherence less than 0.90. I right-clicked on the band —> Properties —> Valid Pixel Expression (Coherence Band Name > 0.9). After doing so, I noted the information about the pixel with somehow the highest coherence specifically its position.
In my terrain corrected displacement product, I looked for that pixel with high coherence and noted the value of displacement. Then I created a new band following these steps —> Raster —> Band Maths —> (New Band Name) and made the following expression (New Band Name - Pixel displacement value with high coherence).
I do not know if what I did are all correct. I am trying to understand and do what vasilisgeo88 mentioned in one of his posts.
Please take a look of what I am following in my study. I hope we can share ideas. @falahfakhri is also helping me and I am very thankful to him.
Hi! I was looking for the graph showing the effect of temporal baseline on coherence in one of the fora here but unfortunately, I couldn’t find it anymore. Can you please provide me the graph and some relevant papers discussing the effects of temporal baseline and perpendicular baseline in coherence estimation? Thank you.
@ABraun, yes! Thank you so much! So basically, with regards to time and distance, the shorter the temporal baseline (days) and perpendicular baseline (meters) the better the coherence. Am I correct? I’ve read some papers while waiting for this graph and the findings are like that.
Thank you, again! So the effect of perpendicular baseline is indifferent! For my preliminary study, the longest and shortest perpendicular baselines were 97m and 18m, respectively. These do not fall in the range of optimum perpendicular baseline. Will it still be okay? I see some published papers with the same case I have.
For the mean time, I am more focus on the effect of temporal baseline on coherence. Below is a summary showing the relationship between the two I have obtained. Could you tell if this is reasonable? The images I’ve acquired were between October 2014 and December 2016. I have a total of 8 images creating 7 pairs. My master image is the October 2014 SAR image and the slave images have intervals of approximately 3 months from each other.
Sentinel-1 doesn’t provide data above 150 m (unfortunately), so this is okay. I’d still say, the longer the better.
Coherence image look reasonable, I think most of the decorrelation (decrease of coherence) happens during the first month.
P01-P20 were selected points in my AOI. I’ve selected these points or pixels that showed high coherence (0.50 and above) from my previous set of images (from another path with same frames and polarization which is VV). But I was surprised when I used another set of images and analysis schedule. I did coherence mask and those points (almost all) were gone for temporal baseline greater than 96 days. But of course, I’ve managed to get the coherence values less than 0.50 as well as the corresponding displacement of these selected pixels. Below is my displacement vs temporal baseline summary. Zero (0) baseline is my single master image. I just do not know yet if this graph is ‘interpretable’.
In general as I mentioned before these results are reasonable, but according to statistics method the neutrality should be taken in account in order to selecting samples, the best way of that is the random selections (of course there are many methods for sample selecting) But in your case here you decided to select the coherence > 0.5 , ,
I’d suggest to you to compare the coherence of the whole interfereograms, in that case when you’ll get similar to the results you got, this will promote your work.
Would you please to add up the reference in here, But basically the <=0.35 is not coherent, I think in case you mentioned, the researchers tried up to retrieve the coherence as much as they could. Furthermore because of the low coh. in their AOI, But please add up the reference in here.
I have acquired 17 images between 2014-10 and 2016-12, Path 127, Frame 120, VV, Ascending Orbit.
I also have acquired 6 images between 2015-11 and 2016-04, Path 127, Frame 119, VV, Ascending Orbit. These 6 images actually fill the big gap that I have between 2014-10 and 2016-12.
I also have acquired 1 image on 2016-07 which also is in the gap also, Path 127, Frame 117, VV+VH, Ascending Orbit.
I will try to stack two images from different frames and see how if it works. Or would you tell me already if it will work?
I will not try stacking images with different polarizations.