How can I know the value of satellite altitude for a particular Sentinel 1A image

I am not sure the value of the altitude is given as a metadata parameter.

To calculate it:

- take the x,y,z position values of one of the orbit state vectors (look for â€˜orbitListâ€™ in the annotation files of that image or in the precise orbit files). This is a list of vectors; just take the first vector, the middle one, or calculate the altitude for each one of them and do the mean. x,y,z are the coordinates (in metres) in an Earth Centred Earth Fixed (ECEF) reference frame.
- convert the ECEF coordinates to lat,lon,alt, for instance using the online tool: http://www.oc.nps.edu/oc2902w/coord/llhxyz.htm

This altitude will be referenced to the ellipsoid.

Thanks a lot