code: def _init_refl3x(self, projectables):
          
          if not Calculator:
              LOG.info("Couldn't load pyspectral")
              raise ImportError("No module named pyspectral.near_infrared_reflectance")
          _nir, _tb11 = projectables
          self._refl3x = Calculator(_nir.attrs['platform_name'], _nir.attrs['sensor'], _nir.attrs['name'])
docs: Initiate the 3.x reflectance derivations.