Refractive Index Of Seawater Research Articles

Measurement Error Analysis of Seawater Refractive Index: A Measurement Sensor Based on a Position-Sensitive Detector.

The seawater refractive index is an essential parameter in ocean observation, making its high-precision measurement necessary. This can be effectively achieved using a position-sensitive detector-based measurement system. However, in the actual measurement process, the impact of the jitter signal measurement error on the results cannot be ignored. In this study, we theoretically analysed the causes of long jitter signals during seawater refractive index measurements and quantified the influencing factors. Through this analysis, it can be seen that the angle between the two windows in the seawater refractive index measurement area caused a large error in the results, which could be effectively reduced by controlling the angle to within 2.06°. At the same time, the factors affecting the position-sensitive detector's measurement accuracy were analysed, with changes to the background light, the photosensitive surface's size, and the working environment's temperature leading to its reduction. To address the above factors, we first added a 0.9 nm bandwidth, narrow-band filter in front of the detector's photosensitive surface during system construction to filter out any light other than that from the signal light source. To ensure the seawater refractive index's measuring range, a position-sensitive detector with a photosensitive surface size of 4 mm × 4 mm was selected; whereas, to reduce the working environment's temperature variation, we partitioned the measurement system. To validate the testing error range of the optimised test system, standard seawater samples were measured under the same conditions, showing a reduction in the measurement system's jitter signal from 0.0022 mm to 0.0011 mm, before and after optimisation, respectively, as well as a reduction in the refractive index's deviation. The experimental results show that the refractive index of seawater was effectively reduced by adjusting the measurement system's optical path and structure.

High-Sensitivity Seawater Refraction Index Optical Measurement Sensor Based on a Position-Sensitive Detector.

The refractive index of seawater is one of the essential parameters in ocean observation, so it is necessary to achieve high-precision seawater refractive index measurements. In this paper, we propose a method for measuring the refractive index of seawater, based on a position-sensitive detector (PSD). A theoretical model was established to depict the correlation between laser spot displacement and refractive index change, utilizing a combination of a position-sensitive detector and laser beam deflection principles. Based on this optical measurement method, a seawater refractive index measurement system was established. To effectively enhance the sensitivity of refractive index detection, a focusing lens was incorporated into the optical path of the measuring system, and simulations were conducted to investigate the impact of focal length on refractive index sensitivity. The calibration experiment of the measuring system was performed based on the relationship between the refractive index of seawater and underwater pressure (depth). By measuring laser spot displacement at different depths, changes in displacement, with respect to both refractive index and depth, were determined. The experimental results demonstrate that the system exhibits a sensitivity of 9.93×10-9 RIU (refractive index unit), and the refractive index deviation due to stability is calculated as ±7.54×10-9 RIU. Therefore, the feasibility of this highly sensitive measurement of seawater refractive index is verified. Since the sensitivity of the refractive index measurement of this measurement system is higher than the refractive index change caused by the wake of underwater vehicles, it can also be used in various applications for underwater vehicle wake measurement, as well as seawater refractive index measurement, such as the motion state monitoring of underwater navigation targets such as AUVs and ROVs.

Optical Properties of Body Mucus Secreted from Coral Reef Sea Slugs: Measurement of Refractive Indices and Relative Absorption Spectra.

Sea slugs are always covered in a mucus layer that has various functions including chemical defense that often involves aposematism and mimicry. Therefore, it is necessary for sea slugs to exhibit their body colors and patterns exactly, and the optical properties of mucus should support this requirement. We examined body mucus from heterobranch sea slugs collected in the Okinawan coral reefs. The refractive indices of mucus from 32 species ranged from 1.3371 to 1.3854 and were similar or slightly greater than the refractive index of seawater (ca. 1.34), indicating that light reflectance on the mucus layer is generally small. Moreover, dissolution of mucus into seawater would form a gradient of refractive indices and enhance the reduction of reflectance. We also obtained relative absorption spectra of the mucus from 32 species. In the range of visible light, absorption spectra of mucus suggest that the mucus layer is almost transparent and is not likely to interfere with the body colors. The presence of absorption peaks and/or shoulders in the UV (ultraviolet) range (280-400 nm) indicates that the mucus layer potentially serves as a sunscreen that absorbs UV radiation in 23 species, whereas prominent UV absorption was not found in the other 9 species. In a kleptoplasty sacoglossan Plakobranchus ocellatus, the refractive indices and presence or absence of UV-absorption showed that the optical properties of the mucus varied to some extent but did not show seasonal fluctuation. The UV-absorption in the mucus may also protect kleptoplasts in kleptoplasty sacoglossans. The present results support the importance of mucus as a functional optical layer for the shell-less life of sea slugs.

Drift Error Compensation Algorithm for Heterodyne Optical Seawater Refractive Index Monitoring of Unstable Signals.

The refractive index measurement of seawater has proven significance in oceanography, while an optical heterodyne interferometer is an important, highly accurate, tool used for seawater refractive index measurement. However, for practical seawater refractive index measurement, the refractive index of seawater needs to be monitored for long periods of time, and the influence of drift error on the measurement results for these cases cannot be ignored. This paper proposes a drift error compensation algorithm based on wavelet decomposition, which can adaptively separate the background from the signal, and then calculate the frequency difference to compensate for the drift error. It is suitable for unstable signals, especially signals with large differences between the beginning and the end, which is common in actual seawater refractive index monitoring. The authors identify that the primary cause of drift error is the frequency instability of the acousto-optic frequency shifter (AOFS), and the actual frequency difference was measured through experimentation. The frequency difference was around 0.1 Hz. Simulation experiments were designed to verify the effectiveness of the algorithm, and the standard deviation of the optical length of the results was on the scale of 10-8 m. Liquid refractive index measurement experiments were carried out in a laboratory, and the measurement error was reduced from 36.942% to 0.592% after algorithm processing. Field experiments were carried out regarding seawater refractive index monitoring, and the algorithm-processing results are able to match the motion of the target vehicle. The experimental data were processed with different algorithms, and, according to the comparison of the results, the proposed algorithm performs better than other existing drift error elimination algorithms.

Modeling of the complex refractive index and reflectivity of flat surface water over the Persian Gulf at C-band

For the microwave region of the electromagnetic spectrum, unlike visible light, the imaginary part of the refractive index can be significant, in which case it cannot be neglected. A well-known empirical model is not available for the direct calculation of the complex refractive index of seawater at the microwave region. However, based on the relationship between the refractive index and the permittivity, and by using the models provided for the seawater permittivity at the microwave frequencies the refractive index can be calculated. In this work, complex refractive index and normal reflectivity of Persian Gulf water at the C-band (5 GHz) have been calculated by using electromagnetic equations. The complex permittivity required for computing these parameters has been calculated from the Ellison's empirical model with measured input data. Calculations showed that the annual mean of basin-averaged of real and imaginary parts of the refractive index is 6.074 and 0.415, respectively. The relative spatial and temporal variability of the imaginary part of the refractive index is considerably stronger than its real counterpart. In all seasons, the reflection coefficient at the nadir in the western half of the Gulf is slightly higher than the eastern half and it has a minimum value of 0.5230 over the southeast waters in the summer and a maximum value of 0.5250 over the northwest waters of the Gulf Persian in winter.

RESEARCH ON REEF BATHYMETRIC SURVEY OF UAV STEREOPAIR BASED ON TWO-MEDIUM PHOTOGRAMMETRY

Abstract. This paper is based on the principles of two-medium photogrammetry, with the purpose to perform a bathymetric survey of a reef in the South China Sea, using aerial imagery acquired by UAV. The first objectives are to introduce the basic principles of two-medium photogrammetry, discuss the technical requirements of this methodology to determine an accurate refractive index of sea water, and propose a new method to calculate seawater refraction and calculate corrected reef elevations. The second objective is to analyse and integrate the elevation and depth datum for both the land mass and the undersea reef. The final objective of this paper is performing stereoscopic mensuration on the UAV photography in order to transform reef elevation and depth datum. Our test shows that aerial two-medium photogrammetry is feasible in practical application, but requires relatively high aerial photography conditions.

RESEARCH ON REEF BATHYMETRIC SURVEY OF UAV STEREOPAIR BASED ON TWO-MEDIUM PHOTOGRAMMETRY

This paper is based on the principles of two-medium photogrammetry, with the purpose to perform a bathymetric survey of a reef in the South China Sea, using aerial imagery acquired by UAV. The first objectives are to introduce the basic principles of two-medium photogrammetry, discuss the technical requirements of this methodology to determine an accurate refractive index of sea water, and propose a new method to calculate seawater refraction and calculate corrected reef elevations. The second objective is to analyse and integrate the elevation and depth datum for both the land mass and the undersea reef. The final objective of this paper is performing stereoscopic mensuration on the UAV photography in order to transform reef elevation and depth datum. Our test shows that aerial two-medium photogrammetry is feasible in practical application, but requires relatively high aerial photography conditions.

A novel method to estimate the specific gravity and refractive index of seawater

Seawater is described by a number of physical and chemical parameters that are useful in measurement and analysis of materiel effects. The material dissolved in seawater will not only affect its specific gravity, but also its optical properties, or rather, the degree to which light is refracted as it passes through the sample of water. The specific gravity and refractive index of seawater are related directly to salinity and temperature. In this work, an attempt has been made to develop simple predictive tools to estimate specific gravity and refractive index of seawater as a function of salinity and temperature. Estimations are found to be in excellent agreement with reported data in the literature with average absolute deviation being less than 0.2%.The predictive tool developed in this study can be of immense practical value for engineers to have a quick estimate on the specific gravity and refractive index of seawater without opting for any experimental trials. In particular, process and water treatment engineers would find the proposed method to be user-friendly with transparent calculations involving no complex expressions.

Dependence of sea surface emissivity on temperature‐dependent refractive index

AbstractTheoretical calculations of emissivity difference, Δε, with changing of water temperature from 301 to 279 K are performed at 820 cm−1 using the temperature‐dependent refractive index of sea water recently proposed by Newman and co‐workers. The results are compared with the calculations using the temperature‐dependent refractive index presented in 1977 by Pinkley and co‐workers. The difference in Δε between the two models is as small as ∼0.0003 for emission angles less than 30° . At larger emission angles, the discrepancy in Δε between the two models is notable. For example, Δε are ∼ − 0.0055 and ∼ − 0.0070 for the Newman and Pinkley models, respectively, at an emission angle of 55° . This discrepancy is mainly caused by the fact that the temperature dependence of the imaginary part of the refractive index of the Pinkley model is ∼1.5 times larger than that of the Newman model and the sea surface emissivity is significantly sensitive to the change of imaginary refractive index at this wavenumber. It is important that accurate values of the imaginary part of the refractive index be obtained. Copyright © 2008 Royal Meteorological Society

Fiber-optic interferometric refractometer for deep-water monitoring

A method is proposed for organizing deep-water refractometric studies and fiber-optic interference systems for precise monitoring of the absolute refractive index of sea water at depths up to 1000 m with measuring probes submerged independently or together with underwater equipment.

Fiber-optic interferometric refractometer for deep-water studies of sea water

A fiber-optic interferometric refractometer is proposed for precise monitoring of the refractive index of sea water at depths of 30–100 m by means of a measuring probe controlled automatically from onboard by underwater equipment.

Intercalibration method for underwater three-dimensional mapping laser line scan systems

I present a method to calibrate absolutely a new family of underwater bathymetric laser scanner systems that use a single target range. Depth is calculated by triangulation among the source, the receiver, and the instantaneous position of a single spot produced by a highly collimated laser beam scanned across the target. For calibration, the refractive index of seawater is used to modulate the triangulation parameters rather than use of different target ranges to calibrate for extended range operation. Exploitation of a unique triangulation configuration allows the receiver characteristics to be ignored initially so that the scanner parameters can be determined. This allows the accurate positioning of the laser spot so that the receiver, in turn, can be calibrated. This intercalibration method provides high-resolution parameterization of the source-receiver characteristics and their geometric layout within the system so that an absolute bathymetric calibration can be realized in situ. In addition, a theoretical model derived to develop the methodology can be used to characterize and optimize future designs.

The refractive index of seawater — comparison of experimental values and estimates from binary solution data

The Tait-Gibson parameter, B ∗ , and the refractive index of seawater are estimated from binary solution data. The predicted and experimental values agree closely. The maximum deviations, at S = 40‰, are 1.7 bars for B ∗ and 0.0001 for the refractive index. The results show that binary solution data, analysed on the basis of the Tammann-Tait-Gibson model for aqueous solutions, can be used to predict the properties of seawater of composition different to that of standard seawater.

Prediction of the refractive index of seawater as a function of temperature, pressure, salinity and wavelength

Abstract An equation is given for predicting the absolute refractive index of seawater as a function of wavelength (in the visible region), temperature, pressure and salinity. This equation is based on the pure-water equation of H. Eisenberg, on the Tammann hypothesis and the Tait-Gibson equation of state for seawater. Comparison with experimental results (to 1380 bars) indicate an accuracy of ca. 0.0001 or better is achieved in the T-P range of oceanographic interest.

Investigation of turbulent pulsations of the refractive index of water using a t�pler instrument

Topler instruments are finding ever wider application for the investigation of small-scale turbulence. In this case, both photoelectric [1] and photographic [2] recording is being used. The present article describes the use of a towed Topler instrument with photoelectric recording for investigating the turbulent fluctuations of the refractive index of sea water. The article gives evaluations of the applicability of the instrument, and an example of the measurement results obtained.

The refractive index of seawater as a function of temperature, pressure and two wavelengths

The absolute refractive index of 35·00% seawater for wavelength of 5017 and 6328 Å was determined for a temperature range of 0–30°C and pressures from 0 to 1406 kg/cm 2 (gage) by a Fabry-Pérot interferometer placed in an optical pressure vessel. The average standard deviation of the measurements is 0·00002 and the experimental error is estimated as ±0·00006.

Some implications of the 1940 redefinition of chlorinity

Deep-Sea Research, 1966, Vol. 13, pp. 975 to 976. Pergamon Press Ltd. Printed in Great Britain. Some implications of the 1940 redefinition of chlorinity* W. S. REESURGH (Received 13 January 1966) EFFORTS to refine the relationships of sea water density, electrical conductivity, and refractive index as functions of chlorinity and temperature have led to plans for the redetermination of these properties on a large number of well-distributed sea water samples. The new values will doubtless be compared with those from earlier studies. A precaution that must be taken to obtain a reliable comparison deals with differences in the meaning of chlorinity during the 1930's and implications of these differences on interpretation of properties measured as a function of chlorinity. These differences and their implications have not been specifically mentioned in recent reviews (Cox, 1963, 1965; JOHNSTON, 1964; PARK and BuRr, 1965) and appear to have been overlooked by a number of workers. The word chlorinity was defined by FORCH, KNLrOSEr~ and SORENSON (1902) as the total weight of halides, calculated as chlorine, in a kilogram of sea water. This stated definition was dependent on the choice of atomic weight values. Standard Sea Water provided a convenient working standard. This working standard was independent of changes in atomic weight values since all batches of Standard Sea Water were compared directly or indirectly with a primary standard sea water whose chlorinity was determined according to the stated definition using KCI (1900 atomic weight values) as the standard. By 1940, changes in atomic weight values led to a difference between the stated definition and the working standard of about 0-05 % (0'009~oo). To avoid this difficulty, JACOBSEN and KNtrOSEN (1940) redefined chlorinity as : The number giving the chlorinity in grams per kilogram of sea water sample is identical with the mass in grams of ' a t o m i c weight silver' just necessary to precipitate the halogens in 0'3285233 kilogram of sea water sample. Chlorinity is, according to this definition, independent of changes in atomic weight values and numerically identical to the chlorinity defined by FORCH, KNUDSEN and SORENSON in 1902. Standard Sea Water provides a working standard as before. During the 1930's, comprehensive investigations of the chlorinity and temperature dependence of the electrical conductivity and refractive index of sea water were performed by Dr. Thomas G. Thompson and his co-workers at the University of Washington, Seattle. The values obtained during these investigations have since seen wide use. In their work on electrical conductivity (THOMAS et al., 1934) and refractive index (UTrERBACK et aL, 1934), identical sea water samples were studied. Care- fully purified NaCI (1932 atomic weight values) was used as the standard in their Volhard chlorinity titrations. Standard Sea Water was not mentioned. It should be made clear that their reported chlorinities actually were chlorinities in 1934, but following the redefinition of chlorinity by JACOBSEN and KNtrDSEN (1940), they have become measurements of chlorine-equivalent. These chlorine- equivalent measurements have been widely interpreted as chlorinities, resulting in a number of erroneous tables and interpolation formulae. Since the pertinent atomic weight values were not changed between 1932 and 1940, the ratio of chlorine-equivalent to chlorinity reported by LYMAN and FLEMING (1940) may be used to convert these reliable measurements of chlorine-equivalent to chlorinity. In comparing recent and future work to that of THOMAS et al. (1934) and UTrERaACK et aL (1934), their reported c h l o r i n i t i e s should be divided by 1-00045 to obtain true chlorinities. *Contribution No. 84 of Chesapeake Bay Institute and the Department of Oceanography, The Johns Hopkins University. This study was supported by the Office of Naval Research, under Contract N o n r 4010(11), N R 083-016.