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Development of an in-situ optical detector to measure water turbidity and Chlorophyll content

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Paper number  131620113,  2013 Kansas City, Missouri, July 21 - July 24, 2013. (doi: @2013
Authors:   Qin Zhang, Lihua Zheng, Minzan Li, Yao Zhang, Hong Sun, Zhenjiang Zhong, Xiaoshuai Pei
Keywords:   Turbidity Chlorophyll content in-situ optical detector Comprehensive measurement method Transmission.

Abstract. The turbidity and chlorophyll content of water are very important parameters in aquaculture. An integrated portable optical detector was developed to measure turbidity and chlorophyll content of water body. This instrument is developed based on the comprehensive measurement method by combining scattering light and transmission light to measure turbidity and the transmission method to measure chlorophyll content. It uses AT89S52 microcontroller as its control chip and consists of the light emission unit, detection unit and control unit. Wherein the light emission unit comprises four sets of LED light source (wavelength of 645nm, 663nm and 860nm) and the corresponding collimating lens; the detection unit comprises four photoelectric sensors; the control unit includes the light source driving circuit, the two-stage amplification circuit and the A/D conversion circuit. The Integrated detector was calibrated in laboratory and carried out field experiments in-situ. The experiments showed that the water detector achieved a high accuracy. To the turbidity measurement, we built the sectionalized model, its calibration RL2 was 0.9921 and Rh2 was 0.9736, and the validation RL2 was 0.9996 and Rh2 was 0.9838, with the resolution of 0.01NTU and the accuracy of ± 2%. To the chlorophyll content measurement, after excluding several abnormal points, the calibration R2 was 0.9652 and the validation R2 was 0.8118, with the resolution of 0.01mg/L and the accuracy of ± 2%. The results showed that this optical detector reached the practical level.

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