code: def get_earth_radii(self):
          
          earth_model = self.prologue['GeometricProcessing']['EarthModel']
          a = earth_model['EquatorialRadius'] * 1000
          b = (earth_model['NorthPolarRadius'] +
               earth_model['SouthPolarRadius']) / 2.0 * 1000
          return a, b
docs: Get earth radii from prologue
  
          Returns:
              Equatorial radius, polar radius [m]