Extinction Coefficient Of Water Research Articles

Improvements and Evaluation of the FLake Model in Dagze Co, Central Tibetan Plateau

FLake has been one of the most extensively used lake models in many studies for lake thermal structure simulations. However, due to the scarcity of lake temperature observations, its applicability and performance on lakes over the Tibetan Plateau are still poorly investigated, especially in small- to medium-sized lakes. In this study, based on water profile observations in Dagze Co, a medium-sized lake on the central Tibetan Plateau, the sensitivity of lake thermal features to three key parameters in FLake was investigated. The performance of FLake in reproducing the lake thermal features was evaluated and improved by optimizing these key parameters. The results showed that the FLake model with default parameter settings can generally reproduce the thermal features of Dagze Co, but there are still significant deviations compared to observation. The sensitive experiments demonstrated that the thermal structure of the lake obviously responds to the change in the water extinction coefficient (Kd), friction velocity (u*), and ice albedo (αice). Based on previous studies and sensitive experiments, the three key parameters were set to the optimized value, which substantially improved the performance of FLake. The values of bias and RMSE of simulated lake surface water temperature decreased from 3.08 °C and 3.62 °C to 2.0 °C and 2.48 °C after parameter optimization. The integration of a simple salinity scheme further improved the ability of FLake to reproduce the observed thermal features of Dagze Co. These results will improve our understanding of thermal processes in lakes on the Tibetan Plateau, as well as the applicability of lake models.

How does lake water clarity affect lake thermal processes?

The objective of this study was to determine the effects of water clarity changes on thermal processes in Lake Poyang, the largest freshwater lake in China, using a physically based lake model embedded in the Community Land Model. A water extinction coefficient (Kd) describing water clarity and controlling radiation penetration in the lake model was used to conduct controlled simulations. Three sets of simulations were conducted for Lake Poyang over the period from 2000 to 2015: DEFAULT with the Kd = 0.45 m−1; CTL with the Kd = 1.68 m−1 based on a water clarity of 0.85 m; and DARK with the Kd = 1.68 m−1 from 2000 to 2005 and Kd = 3.44 m−1 based on a water clarity of 0.41 m observed from 2005 to 2015. The simulation results showed that compared with the DEFAULT simulation, the temperature simulations were closer to the observations using the more accurate Kd values for the CTL and DARK simulations. Due to decreased water clarity, radiation absorbed in the top 1 m of the water body was larger for the DARK simulation and lower at greater depths than that observed for the CTL simulation. Such changes in radiation penetration in the DARK simulation generated a higher lake water surface temperature (LWST) and thus stronger lake-air interactions from February to July and lower LWST and turbulent fluxes from August to the following January than in the CTL simulation. The temperature inside the lake water body declined markedly, with a significant reduction from June to August that exceeded 5 °C. The results of this study provide an additional reference regarding lake water clarity effects on inland freshwater systems and theoretical support for lake water system management.

Variance Based Sensitivity Analysis of FLake Lake Model for Global Land Surface Modeling

AbstractGiven the ever increasing spatial resolution of climate models and the significant role of lakes on the regional climate, it becomes important to represent water bodies in climate models. Such developments have started in the IPSL (Institut Pierre Simon Laplace) climate model and its land surface component, ORganizing Carbon and Hydrology In Dynamic Ecosystems (ORCHIDEE), with the Freshwater Lake model, FLake. To answer the questions raised by these new developments, such as the lake differentiation and related model parameters, we analyze spatial distributions of lake characteristics in the whole world to perform a global sensitivity analysis of the FLake parameters. As a result, three different climates and four lake depth configurations were selected as test cases. The Sobol method as sensitivity analysis based on variance decomposition was chosen to rank parameters impact on the model output, that is, lake surface water temperature, latent and sensible heat fluxes. We focus on the 11 parameters of the FLake model, which are the lake depth, the albedo and light extinction coefficient of water, snow, and ice respectively, the fetch, and the relaxation coefficient of the thermocline shape factor. The results show different sensitivity features according to the lake type and climate. The dominant role and time varying contribution of the lake depth, radiative parameters (albedo, light extinction coefficient) and thermocline relaxation coefficient linked to the atmospheric conditions, were clearly highlighted. These findings will lead us to distinguish between different lake categories in each grid cell of ORCHIDEE in the future implementation.

A reagentless and rapid method to measure water content in oils

A simple method for measuring water levels from 1 mg L−1 to 5000 mg L−1 in oils that uses no chemical reagents or matrix specific calibrations is described. The approach involves capturing the water from the oil on an infrared transparent membrane and then recording an IR spectrum in transmission mode through the membrane. A classic spectrum of liquid water is obtained for all oil types, as both dissolved water and emulsion-based water are extracted to form an adsorbed layer of water on the membrane surface. The method was tested with three types of oils that are identified as difficult in the ASTM method E2412, as these oils, exhibit distortions in the water bands due to interactions of the water with the oil, or have significant levels of scattering due to the presence of water droplets. In comparing water concentrations measured by Karl Fischer titration, a high level of linearity (R2 > 0.995) is obtained over the range of 1 mg L−1 to 5000 mg L−1 with slope values of 0.99 for power steering fluid, 0.98 for vegetable oils, and 0.95 for extreme pressure fluid. This shows that water concentration obtained by the membrane method were comparable to those obtained by Karl Fischer. No matrix calibrations were needed as the concentration of water in oil was determined using literature values for the extinction coefficients of water. The wide detection range is obtained by varying the volume of oil (30 μL-30 mL) passed through the membrane and by choosing the water band for quantification.

Instrument for measuring the water extinction coefficient under laboratory and field conditions

Instrument for measuring the water extinction coefficient under laboratory and field conditions

Geometric Effects of an Inhomogeneous Sea Ice Cover on the under Ice Light Field

Light measurements in the ocean provide crucial information about the energy fluxes in the climate and ecosystem. Currently radiative transfer problems are usually considered in horizontally homogeneous layers although it is known to be a crude assumption in many cases. In this paper, we examine the effects of a horizontally inhomogeneous sea ice layer on the light field in the water underneath. We implemented a three dimensional model, capable to simulate the light field underneath arbitrary surface geometries using ray optics. The results show clear effects of the measurement geometry on measured fluxes obtained with different sensor types, which need to be taken into account for the correct interpretation of the data. Radiance sensors are able to better sense the spatial variability of ice optical properties as compared to irradiance sensors. Furthermore we show that the determination of the light extinction coefficient of water from vertical profiles is complicated under a horizontally inhomogeneous ice cover. This uncertainty in optical properties of the water, as well as the measurement geometry also limits the possibility to correct light measurements taken at depth for the influence of water in between the sea ice and the sensor.

IR Practical Extinction Coefficients of Water in Alkali Lime Silicate Glasses Determined by Nuclear Reaction Analysis

Infrared spectroscopy (IR) is widely used to determine the water concentration in glasses, whereas determination of the IR practical extinction coefficient is necessary to deduce the absolute water concentration of glasses on the basis of Beer–Lambert law. From the nuclear reaction analysis data, the IR practical extinction coefficients of water were successfully determined for the alkali lime silicate glasses with different levels of sodium/potassium cation (Na/K) ratio. The two‐band method is well‐known to be useful for the determination of the water concentration in some alkali lime silicate glasses. It is proved here that the two‐band method is not applicable to the variety of composition for alkali lime silicate and soda lime aluminosilicate glasses, whereas it is valid for the similar composition of soda lime silicate glasses [SLS: Composition (in mol%) 16Na2O·10CaO·74SiO2]. The single‐band procedure with the IR practical extinction coefficient is crucial for the determination of the precise water concentration in the wide variety of glass composition although the determination of the IR practical extinction coefficient is troublesome. It also appears that the ion radius of alkali affects the IR practical extinction coefficient and the chemical state of OH group in glasses.

胶州湾生物⁃物理耦合模型参数灵敏度分析

The marine ecological models have been widely applied. The key factor limiting application of ecological models is the uncertainty of these models,primarily due to the uncertainty of the parameters used. The purpose for sensitivity analysis of parameters for ecological models was to assess influential degrees of various parameters on simulating outcomes with a particular model,which are the essential procedures for parameter optimization and model calibration and the important tools for understanding the behaviors of the model. In this study,we conducted sensitivity analysis on 50 parameters for five state variables i. e. phytoplankton,zooplankton,nutrient,detritus and dissolved oxygen included in the coupled biological-physical model for Jiaozhou Bay. We found that among 50 parameters,three were highly sensitive,two were sensitive,11 were moderately sensitive and 34 were less sensitive. The highly sensitive and sensitive parameters included phytoplankton growth rate( μ PRPC),factors for dark reaction correction( FAC),light saturation intensity( α), phytoplankton death rate( μ DEPC) and light extinction coefficient of water( bla). They have major impacts on plant growth and death,reflecting the essentialness and importance of phytoplankton in ecosystem. The plant growth process has the most important impacts on the stimulating results. The key factor limiting plant growth is light whereas light extinction of water is the most important factor limiting light intensity. These five parameters have significant impacts on carbon and nutrient cycles,and are the most important parameters in Jiaozhou Bay ecosystem. Thus,they should be optimized with the first priority. The impacts of moderately sensitive parameters are mediated mainly via the influence of nutrient on phytoplankton growth and death,temperature influence on light saturation intensity and the influence on zooplankton growth,grazing and death as well as the impacts of phytoplankton biomass on grazing,chlorophyll a generation,phosphorus release from disposed substances under hypoxia condition and phosphorus absorption by plants. There are different degrees of variations in sensitivity of the state variables and thus,they have different characteristics. The less sensitive parameters-related processes are mainly light extinction of chlorophyll a and detritus,temperature limitation to zooplankton growth,zooplankton grazing,and mineralization of detritus and sediment,mineralization / deposition of detritus and sediment,the inorganic nitrogen-related processes and changes in dissolved oxygen concentration. These processes are influenced not only by model' s internal parameters but also by external factors such as water depth,sea water temperature and pollutions from land-based sources. Moderately and less sensitive parameters affect model's local processes,and thus are the important basis for model calibration. Additionally,four state variables i. e. chlorophyll a,zooplankton,detritus and inorganic phosphorus,are calibrated according to the maximal production constant of chlorophyll a( K CHmax),first-order zooplankton death rate( μ DEZC1),mineralization rate of organic detritus( μ REDC) and half-saturation constant of phosphorus absorption by zooplankton( h UPPP). The sensitivity analysis of nutrient-related parameters has shown that phytoplankton in Jiaozhou Bay is limited by phosphorus and however inorganic nitrogen is principally effected by pollutions from land-based sources. Dissolved oxygen is less sensitive on each parameter.

Practical IR extinction coefficients of water in soda lime aluminosilicate glasses determined by nuclear reaction analysis

Abstract Infrared absorption spectroscopy (IR) is widely used to determine the water content in glasses, whereas determination of the practical extinction coefficient is necessary to deduce the absolute water concentration of glasses on the basis of Beer–Lambert law. On the basis of the nuclear reaction analysis (NRA) data, the IR practical extinction coefficient of water was successfully determined for the glasses with different levels of Al contents. Whereas the two-band method is well known to determine the water concentration in alkali lime silica glasses, we show that the single-band procedure with a practical absorption coefficient is suitable for the determination of the water concentration in soda lime aluminosilicate glasses containing substantial amounts of Al content. A good correlation is confirmed between the non bridging oxygens/tetrahedral cations (NBO/T) ratio and the practical extinction coefficient of water in soda lime aluminosilicate glasses with identical network-modifying cations.

Evaluation of the effect of nanofluid-based absorbers on direct solar collector

As conventional energy sources like fossil fuels are getting rare, cost of energy production has become higher as well as the concern of environmental pollution by burning of fossil fuels among the developed and developing nations. Solar energy is the most vastly available energy and very effective in terms of energy conversion. The most common solar thermal collector used is the black surface as radiant absorber but the thermal energy efficiency is low. In this study, the effect of nanofluid has been analyzed by using as working fluid for direct solar collector. The extinction coefficient of water based aluminum nanofluid has been investigated and evaluated by varying nanoparticle size and volume fraction. The particle size has minimal influence on the optical properties of nanofluid. On the other hand, the extinction coefficient is linearly proportionate to volume fraction. The improvement is promising within 1.0% volume fraction and the nanofluid is almost opaque to light wave.

Satellite remote sensing of water turbidity in Alqueva reservoir and implications on lake modelling

Abstract. The quality control and monitoring of surface freshwaters is crucial, since some of these water masses constitute essential renewable water resources for a variety of purposes. In addition, changes in the surface water composition may affect the physical properties of lake water, such as temperature, which in turn may impact the interactions of the water surface with the lower atmosphere. The use of satellite remote sensing to estimate the water turbidity of Alqueva reservoir, located in the south of Portugal, is explored. A validation study of the satellite derived water leaving spectral reflectance is firstly presented, using data taken during three field campaigns carried out during 2010 and early 2011. Secondly, an empirical algorithm to estimate lake water surface turbidity from the combination of in situ and satellite measurements is proposed. Finally, the importance of water turbidity on the surface energy balance is tested in the form of a study of the sensitivity of a lake model to the extinction coefficient of water (estimated from turbidity), showing that this is an important parameter that affects the lake surface temperature.

A new method for retrieval of the extinction coefficient of water clouds by using the tail of the CALIOP signal

Abstract. A method is developed based on Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) level 1 attenuated backscatter profile data for deriving the mean extinction coefficient of water droplets close to cloud top. The method is applicable to low level (cloud top <2 km), opaque water clouds in which the lidar signal is completely attenuated beyond about 100 m of penetration into the cloud. The photo multiplier tubes (PMTs) of the 532 nm detectors (parallel and perpendicular polarizations) of the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) both exhibit a non-ideal recovery of the lidar signal after striking a strongly backscattering target (such as water cloud or surface). Therefore, the effects of any transient responses of CALIOP on the attenuated backscatter profile of the water cloud must first be removed in order to obtain a reliable (validated) attenuated backscatter profile. Then, the slope of the exponential decay of the validated water cloud attenuated backscatter profile, and the multiple scattering factor are used for deriving the mean extinction coefficient of low-level water cloud droplets close to cloud top. This novel method was evaluated and compared with the previous method which combined the cloud effective radius (3.7-μm) reported by MODIS with the lidar depolarization ratios measured by CALIPSO to estimate the mean extinction coefficient. Statistical results show that the extinction coefficients derived by the new method based on CALIOP alone agree reasonbably well with those obtained in the previous study using combined CALIOP and MODIS data. The mean absolute relative difference in extinction coefficient is about 13.4%. An important advantage of the new method is that it can be used to derive the extinction coefficient also during night time, and it is also applicable when multi-layered clouds are present. Overall, the stratocumulus dominated regions experience larger day-night differences which are all negative and seasonal. However, a contrary tendency consisted in the global mean values. The global mean cloud water extinction coefficients during different seasons range from 26 to 30 km−1, and the differences between day and night time are all positive and small (about 1–2 km−1). In addition, the global mean layer-integrated depolarization ratios of liquid water clouds during different seasons range from 0.2 to 0.23, and the differences between day and night also are small, about 0.01.

Improvement in underwater phase measurement of an amplitude-modulated laser beam by polarimetric techniques

The phase of the amplitude-modulated radiation reflected by a Lambertian target immersed in water was measured by using a linearly and circularly polarized sounding laser beam. Different values of the water extinction coefficient in the range of 0.06 - 2 m(-1) were realized by adding skim milk as a scattering element. It is shown that very efficient rejection of optical noise, resulting in reliable phase measurements, is accomplished with a cross-polarized and copolarized detection scheme for linear and circular polarization, respectively. The experiment demonstrates that phase measurements are very sensitive to optical noise suppression and that, as far as single scattering is the main involved mechanism, significant improvements can be achieved by adopting a polarization control on both the transmitter and the receiver stages of the apparatus.

Potential Effects of Climate Warming on Fish Habitats in Temperate Zone Lakes with Special Reference to Lake 239 of the Experimental Lakes Area (ELA), North-Western Ontario

We used simple statistics (e.g. mean temperature, degree days, cumulative volume days) to describe present thermal habitats for cool water (yellow perch, Perca flavescens) and cold water (lake trout, Salvelinus namaycush) fish of a small boreal lake. We then modelled changes in the vertical and temporal extent of these habitats under various scenarios of climatic change that included increases in air temperature of 2°C, 4°C, and 9°C, and positive and negative deviations from present levels of 10% in solar radiation and relative humidity, and 20% in wind speed and the lake water extinction coefficient. Model simulations indicated pronounced changes in the temporal and vertical availability of fish thermal niche space. These changes were mainly driven by the large increases in mean mixed layer temperatures that corresponded to ∼85% of the increases in air temperature, but, in particular, changes in light attenuation also resulted in some non-linear, unexpected effects in the distribution and seasonal availability of thermal niche space. As expected, ‘classical’ lake trout thermal habitat (5–15°C) was progressively reduced and almost disappeared in littoral areas in spring and early summer. Perch thermal niche space expanded for air temperature increases of up to 4°C, but largely disappeared for the 9°C increase. We discuss changes in thermal habitat with regard to the life history of lake trout and yellow perch, and include other determinants of fish habitat to evaluate the potential of these species for long-term ecological success under climatic warming.

A plant growth model for integrated weed management in direct-seeded rice: II. Validation testing of water-depth effects and monoculture growth

Manipulating water depths and timing is a key management practice in rice cropping systems, but rice models have not simulated water-depth effects on plant growth. A new plant growth model, DSRICE1, simulates most cultural and weed management practices except fertility. Water-depth effects on plant light capture are mechanistically simulated as reflection and attenuation of light by water. Light attenuation by water in the model depended on water depth and the light extinction coefficient of water, k H 2O (m −1). DSRICE1 was validation tested for prediction of monoculture growth, and specifically for early-season water-depth effects. Analyses revealed that attenuation by water limited irradiance and reduced seedling growth, and indicated which plant traits contributed to growth during submergence. Reflection did not affect rice growth and may be ignored. In empirical validation tests, DSRICE1 predictions were compared with data from 14 independent data sets. For growth up to 40 days after seeding (DAS) (11 experiments), simulations without water-depth effects failed validation tests by overpredicting rice shoot dry mass (DM). In contrast, DSRICE1 simulations with water-depth effects included were accurate with k H 2O from 1 to 4, k H 2O =3 was best overall, and predictions improved with experiment-specific k H 2O values. DSRICE1 also accurately predicted differences in shoot DM per plant in a 1985 water-depth study, while again simulations without water-depth effects did not. Thus, water-depth effects were required to simulate early rice growth accurately. In whole-season empirical validation tests (14 experiments), DSRICE1 simulated shoot, stem, leaf, live leaf, and live stem DM accurately, especially considering the range of data used and the fact that no calibration was needed. DSRICE1 was also corroborated by the fact that it accounts for many physical factors and plant traits that affect submergence tolerance. The model or the techniques it uses may be useful in analyses of cultivar tolerance to submergence. In some respects, DSRICE1 was subjected to more rigorous validation testing than previous rice models, and potentially explains more interactions between rice and weed growth and management. This approach may broaden and improve simulation analyses of integrated weed management in direct-seeded rice systems.

Influence of environmental parameters on the biomass development ofRuppia drepanensis populations in Doñana National Park: the importance of conditions affecting the underwater light climate

The development of submerged plant communities dominated byRuppia drepanensis Tineo in the brackish marsh of the Donana National Park (SW Spain) was coupled to seasonal variation in environmental factors for two consecutive years. Plant biomass increased rapidly in early spring (March), with steady biomass yields (up to 100 g afdw m−2) together with abundant flowering and fruiting in late spring (April–May). Wind-induced sediment resuspension and periphyton growth strongly influenced the light climate experienced by the submerged vegetation, while a phytoplankton effect was generally negligible. Development of the submerged vegetation coincided with a decrease in water extinction coefficient and in bicarbonate concentration. Thus, where dense macrophyte meadows develop, light climate probably is the limiting factor in the early spring, while temperature and bicarbonate levels are so by the end of the season. Interannual variation was found to be very high, both in abundance and distribution of the submerged vegetation, mainly because of differences in rainfall which influenced the inundation cycle. Grazing by waterfowl accounted also for this effect, as in dry years birds concentrate in the few wetlands still containing water.

Effects of water turbidity and salt concentration levels on penetration of solar radiation under water

Two large, outdoor tanks were constructed in order to investigate the effects of water turbidity and salt concentration levels at various depths of water on penetration of solar radiation. These experiments were followed by a laboratory investigation that measured spectral transmittance and the extinction coefficient of water at different salt concentrations and turbidity levels. Both the outdoor and laboratory results indicate that the salt concentration level does not significantly affect solar radiation penetration. However, water clarity, quantified in terms of the turbidity level, plays a critical role on the magnitude of the solar radiation penetration, with the effect of turbidity on penetration increasing with the depth of water. A best-fit model is developed that gives the solar radiation penetration as a function of turbidity level and depth of water.

Solar energy at various depths below a water surface

The total solar energy at various depths in water has been calculated by adopting two sets of data, namely the extinction coefficient of water in the spectral range of 300–2500 nm, and the solar spectrum at sea level in the same spectral range. With the aid of a computer program designed for this purpose, the solar spectrum at various depths has been reconstructed and the total solar energy has been measured by calculating the area under the spectral distribution curves. A mathematical expression for the integrated solar energy as a function of depth in water has been derived.

Near infrared study of aqueous rare-earth ethylsulfates

The near infrared spectra of aqueous solutions of the ethylsulfates of La, Nd, Gd, Tb, Er, Yb, Lu, Y, and Na have been determined from about 0.2 mol-dm−3 to nearly saturation. The extinction coefficients of water have been calculated taking into account the absorption of ethylslfate anions determined in separate experiments. Their values appeared to be nearly the same as that of pure water. The relative contents of free OH groups in 0.5 and 0.7M solutions have been estimated from the absorbances at 1160 nm. They were lower in solutions of the heavy rare-earth ethylsulfates (Tb, Er, Yb, Lu) than in equimolar solutions of the lighter ones (La, Nd), confirming our previous view that secondary hydration of the heavy trivalent rare-earth cations is distinctly stronger than that of the lighter ones. A comparison of the spectra of these aqueous ethylsulfates with those of perchlorates shows that the structure-breaking ability of the C2H5SO 4 − ion is much smaller than that of perchlorate anion.

Vacuum-Ultraviolet Study of Liquid H2O and D2O

Vacuum-ultraviolet spectra of liquid D2O and H2O have been obtained at several temperatures in the wavelength range 1300–1750 Å. Because of the very large extinction coefficient of water in this region, the absorption spectra were obtained from very thin liquid films. The results show that the vapor–liquid shift is to the blue by some 7000 cm−1. The spectra are discussed in terms of the effect of temperature on hydrogen-bonding properties of the liquids in the ground state and the nature of the electronic transitions from which they arise.