DEALING WITH UNCERTAINTY IN RAINFALL GAUGES CALIBRATION: THE QM-RIM METROLOGICAL VALIDATION

Accurate metrological validation is a crucial issue in testing the performance of any calibration apparatus. Reliability of calibration is in fact strictly connected with the capability in controlling and managing inherent calibration uncertainties. In this paper, we handle the metrological validation of the "Module for Qualification of Rainfall Intensity Measurements " (QM-RIM) developed at the Laboratory of DIAM (Dept. of Environmental Engineering of the University of Genova) and here tested in the period from March 2002 to May 2004. The laboratory is one of the three recognized laboratories involved in the WMO Intercomparison of Rainfall Intensity (RI) Gauges started in September 2004. The QM-RIM is an automatic device designed for the calibration of pluviometric instruments by means of a simply reproducible laboratory procedure and able to provide calibration curves for different types of rain gauges. Metrological analysis is here performed in terms of “a priori ” error estimation (Type B errors). All the proposed standard procedures refer to the typologies of systematic and statistical errors as defined in the ISO Guide to the Expression of Uncertainty in Measurement (International Organization for Standardization, Geneva, Switzerland, 1993). We describe the methodology adopted, the main results obtained from the initial testing period, the error assessment procedures, and the uncertainty budget analyses performed on the calibration apparatus