Snap - Snaphu & Baseline

HI! I have 2 sentinel 1 SLC image, with baseline 172m. I do Insar interferometry process with snaphu, so export and previus to "unwrapper " option, I read the config file, and now the baseline is setted to other baseline. Is an error? I can´t understand what is going on there…

aosaocom sentinel baseline Snaphu

the perpendicular baseline is estimated for SLC products and can change after application of the orbit file. This is what we observe in the Stack Overview 170.92 (before) and 172.18 (after).

The difference between SNAP (172) and snaphu (215) is interesting and I do not have an explanation, so far. But I would be interested if this has an impact on the unwrapping result. So if you want to copy the snaphu folder, change the BASELINE value to 172 and run it again, we could compare if the results.

Maybe someone knows why the value used by snaphu is different.

I have made the comparision, and this are the results. I will wait for your opinions.

Could you please adjust the color scale so that 172 and 215 have the same range.
You can transfer it in the Color Manipulation tab, as explained here: SNAP taking a lot of time processing sentinel-1 dual pol SAR data for H-A decomposition

What do I see in the picture of the first post is Bperp and not the baseline itself. I wouldn’t recommend to change values in the snaphu.conf

Here are the both with same color
first 215, second 172.

thank you - that is interesting. So the larger baseline (215, left) produces higher terrain variation) than the smaller one (172, right). Which one is closer to the SRTM data? You could calculate a difference image to test.

I have no idea why the values are different in SNAP and snaphu, but we should clarfiy it, as it makes a real difference.

@lveci @jun_lu Do you have an explanation why the baseline in the snaphu metadata differs from the one from SNAP?

@ABraun @guidopilato In my post above I noted that baseline and perpendicular baseline are different things . I guess the misinterpretation is obvious.

I made some processing recently and therefor I publish two screenshots

1st Is the stack overview operator

2nd is the snaphu.conf

I hope the difference is visible now.

@hriston_bg How do you call them ? I mean, i understand they are different things(thanks for that), but i want to be sure going from baseline to perpendicular baseline, or vice versa. Thanks again

@guidopilato Below is short answer to your question

The figure shows a sketch of the acquisition geometry for repeat pass interferometric acquisition. The vector between the two orbital positions at times 𝑡0 and 𝑡1, respectively, is called the baseline. The components of the baseline along (Δ𝑅) and across (𝐵⊥) the direction from satellite to target influence the range difference Δ𝑅 between the two acquisitions, and hence the interferometric phase.


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this could indeed be the reason for the different values. Thank you @hriston_bg, for raising this point.

I just wanted to share the info I have. :smile:

I also highly recommend all the colleagues here to spend some time to read the whole document in the link I put as last line in my previous message.