# S1 incident angle to do decomposition

Dear all,

I would like to decompose both ascending and descending orbits of S1 into vertical and horizontal directions. So, I need to have the incident angle of any pixel. I found it at the metadata section of the image but I am a little bit worried about it is possible to use it for decomposition or not? and also how can I export latitude, longitude, and incident angle as a matrix or tiff to open in Matlab software?

After the InSAR processing, when I open the properties of the incident angle, longitude or latitude, I faced that their dimensions are not the same with the displacement. Why?

Best regards,
Sayyed

Hi Sayyed,

Using the Terrain Correction operator you have the options to export the Orthorectified Latitude/Longitude, as well as the incident angle (from ellipsoid, local, or projected local) so you can check even the difference between them.

Additionally during the Terrain Correction you can define the projection and the final pixel spacing.

I hope I answered your questions!
Let us know

Dear Dr. Delgado,

Your answer is great and so helpful. I think I must use the incident angle from ellipsoid to do the decomposition. Is it true?

Best regards,
Sayyed

In case of high topography I would actually suggest the projected local incident angle.
In flat areas when the monitored area is small the incident angle from ellipsoid and the other two are quite similar. I would suggest to use either the local or the projected local.

Again, you may like to try them all so you can better understand their differences.
I hope this helps.

Thank you so much. I got it very well.

Excuse me, I checked the max and minimum value of incident angle from ellipsoid, local, and the projected local. As you can see in the following, the local incident angle and projected local incident angle are quite similar but the incident angle from ellipsoid is not the same.

My study area is located in the center of Iran, which is a mixture of desert and mountains. You can see the figure of my study area in the following and I need to study three earthquakes happened in this area. So, I do really appreciate if you guide me about choosing the correct option of incident angle.

Best regards,
Sayyed

As I said, incident angle from ellipsoid is only similar to local incident angle in flat areas when the AOI analysed is small.

Please check in the literature which incident angle they normally use, but my first impression is to get either the local incident angle or the projected local incident angle, as they would better describe the movement along the “real” surface. Please somebody correct me if I am wrong.

I hope this helps.