Chirp modulation enabled turbidity measurement for large scale monitoring of fresh water

Monitoring water turbidity accurately at a large scale provides vital information to alert abnormal water pollution event. However, scientists and engineers have to make the tradeoff among accuracy, range, and cost of turbidity measurement solutions. Consequently, the state of the art solutions utilize high-end hardware configurations to maintain high accuracy at wide dynamic range, which are either too expensive or complex to be adopted in large-scale monitoring. A low cost turbidity sensor without compromising on accuracy and dynamic range raises a big challenge. This paper approaches this challenge with Chirp modulation and signal convolution in the statistical domain, which can provide more than 40 dB gain with traditional low-cost photodiode. The proposed solution can significantly increase the system performance scaled with hardware configurations. As a result, the implemented proof of concept system can provide as high as 2% measurement accuracy over a wide range of 0–1000 NTU with low-cost hardware configurations.