code: def radiance(self, band):
          
          ml = getattr(self, 'radiance_mult_band_{}'.format(band))
          al = getattr(self, 'radiance_add_band_{}'.format(band))
          dn = self._get_band('b{}'.format(band))
          rad = ml * dn.astype(float32) + al
  
          return rad
docs: Calculate top of atmosphere radiance of Landsat 8
          as outlined here: http://landsat.usgs.gov/Landsat8_Using_Product.php
      
          L = ML * Q + AL
      
          where:
              L  = TOA spectral radiance (Watts / (m2 * srad * mm))
              ML = Band-specific multiplicative rescaling factor from the metadata
                   (RADIANCE_MULT_BAND_x, where x is the band number)
              AL = Band-specific additive rescaling factor from the metadata
                   (RADIANCE_ADD_BAND_x, where x is the band number)
              Q  = Quantized and calibrated standard product pixel values (DN)
                   (ndarray img)
      
          Returns
          --------
          ndarray:
              float32 ndarray with shape == input shape