CEN/TC 318/WG 12 - Measurement of rainfall intensity

Non-catching type gauges are the emerging class of in situ precipitation measurement instruments. For these instruments, rigorous testing and calibration are more challenging than for traditional gauges. Hydrometeors’ characteristics like particle size, shape, fall velocity and density need to be reproduced in a controlled environment to provide the reference precipitation, instead of the equivalent water flow used for catching-type gauges. They are generally calibrated by the manufacturers using internal procedures developed for the specific technology employed. No agreed methodology exists, and the adopted procedures are rarely traceable to internationally recognized standards. This document describes calibration and accuracy issues of non-catching instruments used for liquid/solid atmospheric precipitation measurement. An overview of the existing models of non-catching type instruments is included, together with an overview and a description of their working principles and the adopted calibration procedures. The literature and technical manuals disclosed by manufacturers are summarized and discussed, while current limitations and metrological requirements are identified.

This document considers liquid atmospheric precipitation and defines the procedures and equipment to perform laboratory and field tests, in steady-state conditions, for the calibration, check and metrological confirmation of liquid precipitation measurement instruments. It provides a classification of catching-type measurement instruments based on their laboratory performance. The classification does not relate to the physical principle used for the measurement, nor does it refer to the technical characteristics of the instrument assembly, but is solely based on the instrument calibration. Attribution of a given class to an instrument is not intended as a high/low ranking of its quality but rather as a quantitative standardized method to declare the achievable measurement accuracy in order to provide guidance on the suitability for a particular purpose, while meeting the user’s requirements.

This Technical Report describes a method for calibrating rainfall intensity (RI) gauges and the measurement requirements to obtain accurate and compatible data sets from hydro-meteorological networks, as a forerunner to the development of full hydro-meteorological data collection standards.
This Technical Report deals exclusively with catching-type RI gauges (see Clause 3). It concentrates on the generic calibration, performance checking and estimation of uncertainties for RI gauges. It does not cover specific gauge measurement principles, technical characteristics and technology adopted in the design of RI gauges.

This European Standard specifies the design of a reference raingauge pit. The reference raingauge pit is designed for the liquid precipitation only. The specified details of the pit and the grating, are purposely kept to a minimum in order to allow each raingauge operator latitude in their construction and to suit local conditions.