Incidence angle

How to download the Sentinel-1A images/data (IW mode) of an area with “same” incidence angle"?
Does it is possible to know the incidence angle before downloading the data?

You always know the incidence angle in advance :slight_smile: At least approximately

From the sentinel product definition (https://sentinel.esa.int/documents/247904/1877131/Sentinel-1-Product-Definition) you have (in degree) : (cf page 61/129)

  • IW1 : 32.9
  • IW2 : 38.3
  • IW3 : 43.1

More precisely, it can varies a bit depending on satellite’s altitude and depending on the range within the subswath. Then you have (in degree) : (cf page 30/129)

Minimum orbit altitude :

  • IW1 : 30.86-36.59
  • IW2 : 36.47-41.85
  • IW3 : 41.75-46.00

Maximum orbit altitude :

  • IW1 : 29.16-34.89
  • IW2 : 34.77-40.15
  • IW3 : 40.04-44.28

Just curious : why do you need this information ?

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Thanks a lot.
I need this information for my study, project. I am studying on how the backscatter changes with the age of the plantation/forest. So, it needs incidence angle should be same right?

The incidence angle is not constant on the whole image, but the acquisition geometry is the same for all acquisitions :slight_smile:

Dear qglaude,
in your opinion is it possible to look at how the incidence angle changes during a complete acquisition? I know that it is provided its nominal value but do you think that decoding a RAW S1 data it is possible to retrieve all these possible values for each ISP of the data?

I can’t tell. I never worked with RAW S1 data.

You can visualize the incidence angle value on the whole image in the file IWX_incident_angle.hdr/img into the image directory tie_points_grids

What incidence angle is good for vegetation/forest studies?

The lower, the better.

Start with the ascending and descending tracks that best cover your area of interest. Local incidence angle depends on the topography anyway so I don’t think there’s much point trying to “optimise” it via image selection. Just use what is available and see how well it works.