code: def _ir_calibrate(self, data):
          
          fk1 = float(self["planck_fk1"])
          fk2 = float(self["planck_fk2"])
          bc1 = float(self["planck_bc1"])
          bc2 = float(self["planck_bc2"])
  
          res = (fk2 / xu.log(fk1 / data + 1) - bc1) / bc2
          res.attrs = data.attrs
          res.attrs['units'] = 'K'
          res.attrs['standard_name'] = 'toa_brightness_temperature'
          return res
docs: Calibrate IR channels to BT.