@property<EOL><INDENT>def tau(self):<DEDENT>
return self._tau<EOL>
Property of the transmissivity parameter.

        :getter:    Returns the albedo value which is stored in attribute
                    ``self._tau``
        :setter:    * sets the emissivity which is addressed as ``self._tau``
                      to the new value
                    * updates the parameter dictionary ``self.param['tau']``
        :type:      float