code: def reflectance(self, band):
          
          if band == 6:
              raise ValueError('LT5 reflectance must be other than  band 6')
  
          rad = self.radiance(band)
          esun = self.ex_atm_irrad[band - 1]
          toa_reflect = (pi * rad * self.earth_sun_dist ** 2) / (esun * cos(self.solar_zenith_rad))
  
          return toa_reflect
docs: :param band: An optical band, i.e. 1-5, 7
          :return: At satellite reflectance, [-]