# Plotting backscaterring (Sigma0 )versus coherence

Dear all,
I am doing interferometry with Sentinel1 (IW mode). I used two images and made coherence and interferogram.

Now, I want to plot sigma0 (dB) of image1 versus coherence two images. I do not know how can I do this by SNAP. I saw some videos about plotting in SNAP but I do not think so they can be related to ‘Sigma0 versus coherence’.

I saw one example with Cosmos-skymed satellite in this paper ‘X-Band Interferometric SAR Observations of Baltic Fast Ice’ but I do not know how can I do that by snap? Should I use pin manager or something else?

Correlative plot ‘Sigma0 versus coherence’ picture by Cosmos-skymed here. I want something like this.

You need to generate two things out of your products (image A and B ):

1. The stack which is needed to calculate your interferogram and the coherence C
2. Calibrate image A (or B) to retrieve Sigmao S

Use the scatter plot to draw the values of C against S:

Note that this is only possible if both rasters have the same extent:

I don’t know why it was done for only few points in your example and also where the ranges at those points come from.

Yes. I want to choose just a few points from my sigma0 and coherence images but with same coordinates (Not whole image). It comes back to our study goal.

1. How we can plot only few points from sigma0 and coherence images?
2. I used pins for taking some points in sigma0 image, then I can export those pins to my coherence picture. It is possible?
Sigma0 image:

Coherence image:

Dear Abraun

1. First of all, you told me, I should Calibrate image A (or B) to retrieve Sigmao S. As my images (A and B) are in IW mode, I used SLC to GRD and then, I did like this on GRD image:
Raster……Data convertion…linear to/from Db
So I have sigma0-vv-dB
Am I right?
2. As you told me both rasters (Image A or B (S) and coherence ©) have the same extent. It means to use the Band Maths they must have the same width and height but how can I do?
First for coherence, I use subset and choose Geo coordinates of my area of interest that it hgas coherence and subset that area and then, I go image A or B and again I use same Geo coordinates but when I look at width and hight, I can see, they are not same.
What can I do now?

Image A or B:

Coherence:

for InSAR you need SLC products, your coherence image is in slant geometry.
as you said, you calculated Sigma0db based on a GRDH product. This is already pre-processed (squared pixels) so you also need to have the Sigma0db layer in slant geometry. Use the original SLC data to calculate Sigma0.