def __init__(self,data,timedata_column='index',data_type='NAT',
                 experiment_tag='No tag given',time_unit=None):
        """
        initialisation of a LabExperimBased object, based on a previously defined
        HydroData object.
        """
        HydroData.__init__(self,data,timedata_column=timedata_column,data_type=data_type,
                           experiment_tag=experiment_tag,time_unit=time_unit)