def METHOD_NAME(self, unit='kelvin'):
    """Returns the soil surface temperature
    :param unit: the unit of measure for the temperature value. May be:
        '*kelvin*' (default), '*celsius*' or '*fahrenheit*'
    :type unit: str
    :returns: a float
    :raises: ValueError when unknown temperature units are provided
    """
    if unit == 'kelvin':
        return self._surface_temp
    if unit == 'celsius':
        return measurables.kelvin_to_celsius(self._surface_temp)
    if unit == 'fahrenheit':
        return measurables.kelvin_to_fahrenheit(self._surface_temp)
    else:
        raise ValueError('Wrong temperature unit')