ISO 23350:2021

Overview

ISO 23350:2021 - "Hydrometry - Catching-type liquid precipitation measuring gauges" defines the typical requirements and functional criteria for catching-type liquid precipitation measuring gauges used in hydrological and meteorological observation. The standard applies to both non‑recording (ordinary and storage) and recording (weighing, tipping-bucket, floating) gauges and covers design features, environmental performance, recording formats, measurement uncertainty and housing - but not site installation specifications or detailed installation conditions.

Key topics and technical requirements

• Gauge types and performance
  • Classifies non‑recording and recording catching‑type gauges; typical resolution 0.1 mm to 1 mm and rainfall intensity capability 0.1 to 1 000 mm·h⁻¹ (or higher).
• Orifice and funnel design
  • Circular orifice with sharp edges; diameter tolerance not to differ by more than 0.2%.
  • Funnel slope recommended at least 45%; vertical wall depth and narrow entrance to reduce splashing and evaporation.
• Environmental ranges
  • Operating temperature: up to +60 °C; minimum 0 °C (standard) or −40 °C with heating/antifreeze for weighing gauges.
  • Relative humidity: 0–100% RH.
• Recording and data
  • Timestamp format: at least 8 digits for date and 8 digits for time (including milliseconds).
  • Rainfall accumulation: at least five digits (not counting the decimal).
  • Recording intervals set by network operator; common intervals: every minute or hourly. Non‑recording gauges are read manually (daily, monthly, etc.).
• Environmental protection and housing
  • Durable, weather‑resistant materials; watertight seams; removable funnel; protection against insects and animal ingress; water‑resistant connectors and markings.
• Measurement uncertainty
  • Guidance on estimating uncertainty (Type‑A, Type‑B and combined methods) and factors affecting measurement precision are included.
• Annexes
  • Annex A: overview of catching‑type gauge types.
  • Annex B: uncertainties associated with different catching‑type gauges.

Applications and users

ISO 23350 is intended for:

• Hydrologists and meteorologists specifying instruments for networks and field monitoring.
• Weather and hydrometric network operators setting data, recording and observation procedures.
• Instrument manufacturers and designers for functional design criteria and performance claims.
• Standards bodies and procurement teams seeking conformity and interoperability requirements.

Practical uses include rainfall accumulation and intensity monitoring for flood forecasting, water resources management, climate studies and operational weather services.

Related standards

• ISO 772 - Hydrometry: vocabulary and symbols (normative reference).
• BS 7843‑3 - Acquisition and management of meteorological precipitation data - code of practice for storage and automatic collecting raingauges (referenced).
• For detailed installation, design of reference pits and solid‑precipitation guidance consult the bibliographic references cited in ISO 23350.

Keywords: ISO 23350, catching-type liquid precipitation measuring gauges, raingauge, hydrometry, precipitation measurement, recording gauges, measurement uncertainty, installation, environmental protection.