How we Measure Turbidity with Optical Accuracy

This dual-technology approach allows for dynamic range detection without the need for manual gain adjustments for higher turbidity levels. 

Application

Turbidity sensors are widely used in environmental monitoring, water treatment, and industrial processes to assess water quality. Their role is increasingly important in subsea applications, where they help evaluate the performance of acoustic and optical instruments in turbid environments. They are also valuable in dredging operations and deep-sea mining, where they monitor sediment disturbance and seabed disruption around extraction sites. 

The Hyperion range includes: 

• A standard model for deep-sea deployment (up to 6,000 m). 

• The Hyperion 32, a compact, cost-effective version for shallower applications (up to 50 m). 
• Also integrated into profiling instruments like the SWiFT (SVPplus Tubidity, and CTDplus Turbidity). 

Advantages 

• Wide dynamic range: Capable of measuring from very low to extremely high turbidity levels. 

• No manual adjustment across turbidity ranges. 

• Consistent performance in a range of environments suitable for both deep and shallow water applications. 

• High sensitivity: Minimum detection level as low as 0.03 NTU. 

• Easily integrates with other systems. 

• Passive sampling and doesn’t alter the sample/environment. 

• Fast and portable and doesn’t require laboratory testing ideal for real-time in situ monitoring. 

Limitations 

• Optical interference, air bubbles, biofouling, or coloured dissolved substances can affect accuracy but this can be alleviated with a shade cap or wiper solution.  

• Only measures close to the face of the sensor, so its range is limited.  

• Non-linear response at extreme turbidity levels requires using look-up tables. 

Additional useful information 

Turbidity in water is measured in Nephelometric Turbidity Units (NTU), with lower values indicating clearer water. The standard method for determining turbidity is outlined in BS EN ISO 7027-1:2016, which specifies quantitative techniques for assessing water clarity. In the UK, the Drinking Water Inspectorate (DWI) sets the regulatory limit for turbidity under the Water Supply (Water Quality) Regulations 2016, stating that levels should not exceed 4 NTU at the consumer’s tap. Water at this level typically appears clear to the naked eye, while turbidity above 5 NTU is usually noticeable to consumers. As turbidity increases, water clarity diminishes, becoming visibly cloudy around 55 NTU and completely opaque beyond 500 NTU. 

Turbidity and Total Suspended Solids (TSS) are closely related measures of water quality. TSS quantifies the actual mass of particles suspended in water, while turbidity measures how much these particles scatter light, affecting water clarity. Generally, higher TSS results in higher turbidity, but the relationship isn’t always direct, as factors like particle size, shape, and composition also influence turbidity levels.