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

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 R L 2 was 0.9921 and R h 2 was 0.9736, and the validation R L 2 was 0.9996 and R h 2 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 R 2 was 0.9652 and the validation R 2 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.