Overview
ISO 9555-4:1992 - "Measurement of liquid flow in open channels - Tracer dilution methods for the measurement of steady flow - Part 4: Fluorescent tracers" defines the use of fluorescent tracers for dilution-type discharge measurements in open channels. The standard describes the commonly used dyes (fluorescein, rhodamine B, acid yellow 7, sulfo rhodamine B, pyranine and rhodamine WT), how to measure them in the field and laboratory, and factors affecting tracer performance such as photochemical decay, adsorption and fluorescence quenching.
Key topics and technical requirements
- Tracers covered: fluorescein, rhodamine B, acid yellow 7, sulfo rhodamine B, pyranine and rhodamine WT. (Notes: fluorescein and rhodamine B were used historically but are not generally recommended for discharge measurement.)
- Measurement principles: fluorimetric analysis (filter fluorimeter or spectrofluorimeter), excitation/emission spectra, and the relationship between fluorescent intensity and tracer concentration.
- Field vs laboratory measurement: guidance on field sampling, sample protection from light (to limit photodegradation), and laboratory analysis procedures.
- Environmental factors: chemical (pH, solvents), physical (temperature, light exposure), biological and adsorption effects that alter tracer signals and accuracy.
- Injection and sampling techniques: practical approaches for tracer injection and representative sampling to ensure adequate mixing and reliable dilution curves.
- Analysis and computations: processing of fluorimetric data to compute steady flow (constant-rate injection or integration/sudden-injection methods) - with supporting analytical procedures (see Annex A for tracer characteristics).
- Instrument considerations: fluorimeter sensitivity, filter selection, and trade-offs between sensitivity and background interference.
Applications and users
ISO 9555-4 is intended for professionals measuring flow in open channels where conventional flow meters are impractical or unsafe. Typical users and applications include:
- Hydrologists and water resources engineers performing stream and river discharge measurements
- Environmental consultants conducting flow assessments for pollution studies or remediation
- Field technicians using tracer dilution methods during floods, low-flow conditions or where channel geometry prevents standard gauging
- Laboratory analysts interpreting fluorimetric data and computing discharge from dilution curves
- Regulatory agencies and research institutions validating open-channel flow data
Related standards
- ISO 9555-1: General principles for tracer dilution methods (constant-rate and integration methods)
- ISO 9555-2: Radioactive tracers
- ISO 9555-3: Chemical tracers
Keywords: ISO 9555-4, fluorescent tracers, tracer dilution methods, measurement of liquid flow in open channels, fluorimeter, fluorescein, rhodamine, pyranine, tracer injection, sampling, flow measurement.