Salinity and turbidity are two important seawater properties in physical oceanography. The study of physical oceanography requires a compact high-resolution in situ salino-turbidimeter to measure these two parameters in different ocean zones. Refractometry has proved to be an effective method to measure seawater salinity with a high resolution. Previous studies have shown that the transmission and scattering of light in a turbid medium impact the light beam deviation measurements, which makes the combination of salinity and turbidity measurements with the same sample mandatory. We analyze the requirements and challenges of a refracto-turbidimeter design from their measurement principles and correlations. According to these requirements, we propose a miniature refracto-nephelo-turbidimeter with a charge-coupled device, providing a salinity measurement resolution of 2 mg⋅kg −1 and a turbidity measurement resolution of 1% of the measurement range. Based on this refracto-nephelo-turbidimeter, different embodiments are discussed to meet the different requirements for different ocean zones.
Salinity and turbidity are two important seawater properties in oceanography. We have studied the use of a high resolution refractometer to measure the salinity of seawater. The requirement of a multifunctional sensor makes the turbidity measurement based on our refractometer valuable. We measure turbidity according to the attenuation of the laser beam caused by the scattering. With the configuration of our refractometer, several issues impact the laser beam attenuation measurement, while the measurement of salinity is impacted by the scattering as well. All these issues make light distribution nonsensitive sensors such as position sensitive devices unsuitable for building the refracto-turbidimeters. To overcome these issues, a charge-coupled device combined with a new location algorithm is used to measure both the refractive index and the attenuation. Several simulations and experiments are carried out to evaluate this new method. According to the results, the way to improve the resolution is discussed as well. The validation of our method is proved by comparison to the nephelometer specified by the nephelometric turbidity unit standard.
A position sensitive device (PSD) is frequently used in laser beam deviation measurement. However, it lacks the capability to retrieve the power distribution information of a laser beam. A charge-coupled device (CCD) gives much more information of a laser beam than a PSD. The requirement of a multifunctional sensor makes the replacement of a PSD with a CCD in measuring laser beam deviation to be a reasonable topic. In this paper a performance comparison between a PSD and a CCD combined with a centroid algorithm are discussed with special attention paid to the CCD-based system. According to the operating principle of the CCD-based system, several experiments were carried out to evaluate five factors of the CCD-based system: image window size, number of processed images, threshold, binning, and saturation. By applying the optimized parameters, several experiments were made to compare the CCD-based system with the state-of-the-art PSD-based system in terms of two performance indicators, namely resolution and speed. It is shown that, by applying the optimized parameters, the performance of a CCD-based system is comparable to that of a PSD-based system in measuring laser beam deviation.
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