Correlating RISAT and Sentinel-1 data

Question

The Sentinal-1 dataset's metadata contain the following values:

range_spacing, azimuth_spacing, incidence_near, incidence_far.

1. What are corresponding names for these values in the RISAT Band_Meta.txt file? It does not have range and azimuth spacings and contains only one incidence angle.

2. Which point in the image has this incidence angle?

3. For my work, I need the incidence angle at every pixel in the image, how do I get it in case of RISAT (for Sentinel, I could do the math using near and far incidence angles and get it but can't do it here)?

Answer 1

Let me answer your queries one by one :

1) For range and azimuth spacing : Look at OutputLineSpacing and OutputPixelSpacing specified within the BAND_META.txt file. As you might be aware, the OutputLineSpacing corresponds to azimuth_spacing and OutputPixelSpacing corresponds to range_spacing.

2)The incidence angle given in the BAND_META file is that of the scene centre.

3)For incidence angle, you can try two different approaches :

a) There are grid files available with the product with name productname_grd.txt, from there you can find out the incidence angle at each point by interpolation. The format of this grid file is explained in the product format, the link of which I am mentioning here : RISAT-1 Product Format

b) You will be able to find a product.xml file alongwith your product. Open that file, where you will find incidenceAnglenear range and incidence angle farrange fields. Utilising these fields, apply interpolation accordingly to get the incidence angle at each pixel.

The first approach utilising grid files will be more accurate.

All the best!!!!!!!!