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• A lake TSI inversion method based on optical mechanism was proposed. • a t-w (440) was confirmed to be the optimal optical characterization parameter of TSI. • DNN model was superior to other models in the inversion of both TSI and a t-w (440). • Trophic status of lakes across China was assessed using the proposed approach. • TSI of 961 lakes in China in 2020 ranged from 6 to 96, with a mean value of 48. Widespread eutrophication has been considered as the most serious environment problems in the world. Given the critical roles of lakes in human society and serious negative effects of water eutrophication on lake ecosystems, it is thus fundamentally important to monitor and assess water trophic status of lakes. However, a reliable model for accurately estimating the trophic state index (TSI) of lakes across a large-scale region is still lacking due to their high complexity. Here, we proposed an optical mechanism-based deep learning approach to remotely estimate TSI of lakes based on Landsat images. The approach consists of two steps: (1) determining the optical indicators of TSI and modeling the relationship between them, and (2) developing an approach for remotely deriving the determined optical indicator from Landsat images. With a large number of in situ datasets measured from lakes (2804 samples from 88 lakes) across China with various optical properties, we trained and validated three machine learning methods including deep neural network (DNN), k-nearest neighbors (KNN) and random forest (RF) to model TSI with the optical indicators and TSI and derive the determined optical indicator from Landsat images. The results showed that (1) the total absorption coefficients of optically active constituents at 440 nm (a t-w (440)) performs best in characterizing TSI, and (2) DNN outperforms other models in the inversion of both TSI and a t-w (440). Overall, our proposed optical mechanism-based deep learning approach demonstrated a robust and satisfactory performance in assessing TSI using Landsat images (root mean squared error (RMSE) = 5.95, mean absolute error (MAE) = 4.81). This highlights its merit as a nationally-adopted method in lake water TSI estimation, enabling the convenience of the acquisition of water eutrophic information in large scale, thereby assisting us in managing lake ecology. Therefore, we assessed water TSI of 961 lakes (>10 km2) across China using the proposed approach. The resulting a t-w (440) and TSI ranged from 0.01 m−1 to 31.42 m−1 and from 6 to 96, respectively. Of all these studied lakes, 96 lakes (11.40 %) were oligotrophic, 338 lakes were mesotrophic (40.14 %), 360 lakes were eutrophic (42.76 %), and 48 were hypertrophic (5.70 %) in 2020. [ABSTRACT FROM AUTHOR]

Distribution, migration and transformation of chromophoric dissolved organic matter (CDOM) in coastal waters are closely related to marine biogeochemical cycle. Ocean color remote sensing retrieval of CDOM absorption coefficient (ag(λ)) can be used as an indicator to trace the distribution and variation characteristics of the Changjiang diluted water, and further to help understand estuarine and coastal biogeochemical processes in large spatial and temporal scales. The quasi-analytical algorithm (QAA) has been widely applied to remote sensing inversions of optical and biogeochemical parameters in water bodies such as oceanic and coastal waters, however, whether the algorithm can be applicable to highly turbid waters (i.e., Changjiang estuarine and coastal waters) is still unknown. In this study, large amounts of in situ data accumulated in the Changjiang estuarine and coastal waters from 9 cruise campaigns during 2011 and 2015 are used to verify and calibrate the QAA. Furthermore, the QAA is remodified for CDOM retrieval by employing a CDOM algorithm (QAA_CDOM). Consequently, based on the QAA and the QAA_CDOM, we developed a new version of algorithm, named QAA_cj, which is more suitable for highly turbid waters, e.g., Changjiang estuarine and coastal waters, to decompose ag from adg (CDOM and non-pigmented particles absorption coefficient). By comparison of matchups between Geostationary Ocean Color Imager (GOCI) retrievals and in situ data, it reveals that the accuracy of retrievals from calibrated QAA is significantly improved. The root mean square error (RMSE), mean absolute relative error (MARE) and bias of total absorption coefficients (a(λ)) are lower than 1.17, 0.52 and 0.66 m-1, and ag(λ) at 443 nm are lower than 0.07, 0.42 and 0.018 m-1. These results indicate that the calibrated algorithm has a better applicability and prospect for highly turbid coastal waters with extremely complicated optical properties. Thus, reliable CDOM products from the improved QAA_cj can advance our understanding of the land-ocean interaction process by earth observations in monitoring spatial-temporal distribution of the river plume into sea. [ABSTRACT FROM AUTHOR]

Comprehensive shielding behaviors of chambersite deposit in China for neutron and gamma ray were systematically analyzed for the first time. Monte-Carlo method simulation technique, American Evaluated Nuclear Data File (ENDF/B-VIII.0), XCOM program and Phy-X/PSD program were used to perform the analysis. Transmission against different neutron resources and cross section for neutrons, mass attenuation coefficient, half value thickness, effective atomic number and electron density for narrow beam gamma ray at 0.001–100000 MeV, and equivalent atomic number, G-P Fitting Parameters, exposure buildup factors and energy absorption buildup factors against wide beam gamma ray for penetration depths up to 40mfp at 0.015–15 MeV were obtained. Shielding performance of chambersite deposit is excellent for high energy and low energy neutrons because of Mn and B respectively, and better than SWX-210. Shielding ability for gamma ray dependent on the element with high-Z or higher content and is between steel-magnetite concrete and ilmenite concrete. The shielding performance for both thermal neutron and gamma ray of the prepared sample is better than SWX-201 and SWX-261. Thus chambersite deposit will be an excellent shielding raw material for both gamma ray and neutron, also combining it with hydrogen rich materials can improve its attenuation properties and expand its possible uses. [Display omitted] • Comprehensive shielding behaviors of chambersite deposit in China for neutron and gamma ray were first analyzed. • Shielding performance of chambersite deposit is excellent for high energy and low energy neutrons. • Shielding ability for gamma ray dependent on the element with high-Z or higher content. • Shielding performance of chambersite deposit is better than some commercial materials. • Chambersite deposit will be an excellent shielding raw material for both gamma ray and neutron. [ABSTRACT FROM AUTHOR]

Upward radiance is the signal source of ocean colour remote sensing. Its attenuation characteristics along with water depth not only determine the water-leaving radiance but are also the key parameters that reflect water-quality conditions. Assuming that the water is optically homogeneous in the vertical direction, this study calculates the attenuation coefficient of upward radiance (ACUR) under conditions with different zenith angles and absorption and scattering coefficients using the radiative transfer model coupled with multiple scattering. Then, the attenuation mechanism of upward radiance is discussed. The results obtained indicate the following. (1) The ACUR under the condition of a large zenith angle gradually decreased and subsequently increased with the increasing scattering coefficient when the absorption was less. The variation trend of the ACUR was gradually weakened with increasing absorption coefficients. (2) The ACUR at a small zenith angle increased approximately linearly with the increasing scattering coefficient; subsequently, this trend gradually disappeared. At the same time, the change rate of ACUR first increased and then decreased with increasing scattering when the absorption coefficient increased. (3) The absorption coefficient has the greatest contribution to the ACUR. When the scattering/absorption ratio is between 0.5 and 37, the corresponding contribution ratio is in the range of 90.3–98.5%. (4) When the ratio is less than 1.5, the contribution of the zenith angle to the ACUR is greater than that of the scattering coefficient, and the corresponding contribution ratios ranged from 2.2% to 7.3% and from 3.7% to 17.9%. With the increasing ratio, the contribution of the scattering coefficient to the ACUR was more than that of the zenith angle, and then this trend became stable. The results were validated by field observation data from Lake Taihu (China). [ABSTRACT FROM AUTHOR]

Temporal and spatial patterns of inherent optical properties in the Bohai Sea are very complex. In this paper, we used 77 groups of field data of AOPs (apparent optical properties) and IOPs (inherent optical properties) collected in June, August, and September of 2005 in the Bohai Sea, to retrieve the spectral total absorption coefficient a( λ) with the quasi-analytical algorithm (QAA). For QAA implementation, different bands in the region 680-730 nm (in 5 nm intervals) were selected and compared, to determine the optimal band domain of the reference wavelength. On this basis, we proposed a new algorithm (QAA-Com), a combination of QAA-685 and QAA-715, according to turbidity characterized by a(440). The percentage difference of model retrievals in the visible domain was between 4.5%-45.1%, in average of 18.8% for a( λ). The QAA model was then applied to Medium Resolution Imaging Spectrometer (MERIS) radiometric products, which were temporally and spatially matched with in-situ optical measurements. Differences between MERIS retrievals and in-situ values were in the range 9.2%-27.8% for a( λ) in the visible domain. Major errors in satellite retrieval are attributable to uncertainties of QAA model parameters and in-situ measurements, as well as imperfect atmospheric correction of MERIS data by the European Space Agency (ESA). During a storm surge in April 2009, time series of MERIS images together with the QAA model were used to analyze spatial and temporal variability of the total absorption coefficient pattern in the Bohai Sea. It is necessary to collect more independent field data to improve this algorithm. [ABSTRACT FROM AUTHOR]

Summary: Sedimentation resulting from soil erosion degrades the surface water environment. This study determines the sediment trapping capacity (STC) of grass filter strips and how slope gradient and vegetation cover affect it. STC is defined as the maximum sediment trapped within vegetative filter strips (VFS) under given conditions. An exponential model was derived to mirror the relationship between instantaneous sediment trapping efficiency and runoff duration, with findings that STC is closely related to the initial efficiency and attenuation coefficients. The model effectively describes the sediment trapping process, and demonstrates that STC decreases with increasing slope and increases with vegetation cover. Grass strips have a small sediment trapping thickness measured in mm or cm, and grass stems and leaves have little influence on STC, which indicates that reasonable forage cutting may have little influence on sediment removal. STC is an intrinsic characteristic of VFS, and it can be recommended to assess the VFS performance in trapping sediment in severe soil erosion areas. A sediment trapping modulus at the watershed scale based on STC, can offer help to effectively evaluate soil and water conservation engineering and transformation of cropland into forest and grassland in China. [ABSTRACT FROM AUTHOR]

The optical properties of tripton, and the correlation between the absorption coefficient and tripton concentration, were investigated based on a large dataset of 727 samples, collected from different regions of shallow Lake Taihu, in China, from July 2004 to April 2007. Four models describing tripton absorption spectra in the visible domain (400-700 nm) were examined to find the optimal model. The conventional single exponential model performed the poorest. Statistically, the most 'useful' model was the hyperbolic model; judged by the root mean square error (RMSE) and the magnitude of the F statistic from an analysis of variance, this was found to give a closer fit for the measured absorption (70.1% reduction in RMSE and 449.7% increase in F value) than did the simple exponential model method. The mean Sd value derived for the hyperbolic model was 5.98 ± 0.30 nm-1, with a very small coefficient of variation of 5.0%. Significant linear correlations were found between ad(440) and total suspended matter, inorganic suspended matter and tripton concentrations, but with the minimal RMSE of ad(440) estimation (0.815 m-1) for tripton. The results demonstrate that it is possible to develop regional models for the estimation of tripton absorption coefficient from the concentration. [ABSTRACT FROM AUTHOR]

In remote chlorophyll-a (chl-a) retrieval in Case-II waters, there always exists some limitations from empirical parameters in the estimating models and uncertainties from the chl-a specific absorption coefficient. In this study, we present a newly improved three-band model in a case study in Shitoukoumen Reservoir for direct calculation of chl-a without any empirical parameters derived from regression. Inherent optical properties of the reservoir were investigated to determine parameters in the improved model. Results show that taking into account variations from chl-a specific absorption, as well as absorption by pure water, the improved model performed well in the field study used for model calibration and also robustly in two other field studies. The findings underline the rationale behind the model and demonstrate a potentially general solution for assessing chl-a in Case-II waters. In the evaluation of P6 data, the traditional near-infrared-to-red reflectance ratio (band 4/band 3) could estimate chl-a with root mean square error below 2.17μg l-1, which confirms that P6 data could be used potentially to determine chl-a concentration. [ABSTRACT FROM AUTHOR]

Abstract: For studies in bio-optical oceanography, visible light properties by classes of dissolved organic matter should be characterized. The regional adjustment of model parameters is one approach which is being widely used to refine bio-optical models. In the present study, buoy and laboratory data were acquired, and during the 15-day observation period an algal bloom event occurred. The absorption coefficient of CDOM at 443nm, ag (443), changed in the range of 0.09–0.35m−1 and 0.1–0.34m−1 for two depths, 0.32m and 2.3m., respectively, throughout the entire period. CDOM absorption was larger for bloom conditions than for non-bloom conditions. In addition, the fraction of CDOM in total absorption was higher during the bloom event than that of non-bloom conditions. The spectral slope of CDOM absorption, Sg , regressed over 400–500nm, ranged from 0.015 to 0.0185nm−1 with an average of 0.0166nm−1. CDOM fluorescence intensity (Fcdom) was obtained using an internal Raman standard and varied over the range of 467.44–1538.23 in relative units. Variations in Fcdom showed a similar pattern to that of CDOM absorption. A robust non-linear relationship between Fcdom and CDOM absorption was found, with a correlation coefficient of 0.893, throughout the whole observation. An attempt to describe Sg with absorption showed a promising consequence that can be described with a negative correlation during the bloom, however, without any distinguishable tendency for non-bloom time span. A two-band ratio algorithm was also carried out for retrieving CDOM absorption. The variations in optical properties of CDOM may be related to the complicated environment in the estuarine waters, which may result from different sources of CDOM. [Copyright &y& Elsevier]

In order to investigate variations of absorption and total chlorophyll- a (TChl- a)-specific absorption coefficient of phytoplankton in Lake Taihu, 57 water samples obtained from Lake Taihu during November 8–22, 2007 were used in this study. Package effect and accessory pigments’ influences on the absorption spectra were also examined. Phytoplankton absorption was measured by quality filter technical, and TChl- a concentration was measured by “hot ethanol” method. Results yielded significant variations in phytoplankton absorption and TChl- a-specific absorption coefficient. Phytoplankton absorption coefficient at 675 nm is highly correlated to TChl- a concentration, while absorption at 440 nm is less correlated to TChl- a concentration because of great package effect and accessory pigments’ influence. There was an inverse relationship between a ph*(λ) and TChl- a concentration. Four types of absorption spectra are identified by normalizing a ph*(λ) to a ph*(440). The a ph*(λ) variation is mainly due to accessory pigments and package effect, whose influence at 675 nm ranges from 83.2% to 28%, with an average of 65.3%. Meanwhile, the wide varying ratio of a ph*(440) to a ph*(675) indicates a large variation range in the ratio of accessory pigment to TChl- a concentration. Those findings are significant to estimate Chl- a concentration based on bio-optical model, estimate primary production from remote sensing, and plan further ecological restoration measures for Lake Taihu. [ABSTRACT FROM AUTHOR]

The concentrations of EC, BC and dust aerosols were determined for atmospheric samples collected from an observation station in Xi'an, China. The results show that the averaged correlation coefficient between EC and BC was founded to be 0.72 with 0.81 ( n = 49) in autumn, 0.70 ( n = 112) in winter and 0.69 ( n = 57) in spring, respectively. Absorption coefficients of dust aerosol were estimated to be 2.7 m2 g−1 in autumn and 4.4 m2 g−1 in winter. The comparison of absorption coefficients of dust aerosol with those of BC implies that BC is the principal light-absorbing aerosol over Xi'an atmosphere. By combining thermal analysis of elemental carbon and dust contents in the aerosol samples, however, the fraction of dust absorption to total light absorption is estimated to be 19% in autumn and 31% in winter, respectively. [ABSTRACT FROM AUTHOR]

Examines the spectral absorption coefficients of the total particulate, nonalgal particulate and phytoplankton pigments in the Pearl River estuary in China and its vicinity waters using the quantitative filter technique. Range of particulate absorption; Typical spectral patterns found for the total particulate absorption; Increase in the chlorophyll-specific absorption coefficients of phytoplankton pigment with decreasing chlorophyll level.

• The main BrC fraction in WSOC and WISOC were HULIS and middle-polar fraction. • The non-fossil carbon was enriched in high polar carbon fractions Oxidized BBOA are the major BrC in HULIS and MP, while primary BBOA are mainly in LP. • More Nitrogen-containing compounds from BB increase the BrC absorption in PRD winter. Atmospheric brown carbon (BrC) is an important constituent of light-absorbing organic aerosols with many unclear issues. Here, the light-absorption properties of BrC with different polarity characteristics at a regional site of Pearl River Delta Region during 2016–2017, influenced by sources and molecular compositions, were revealed using radiocarbon analysis and Fourier transform ion cyclotron resonance mass spectrometry. Humic-like substance (HULIS), middle polar (MP), and low polar (LP) carbon fractions constitute 46 ± 17%, 30 ± 7%, and 7 ± 3% of total absorption coefficient from bulk extracts, respectively. Our results show that the absorption proportions of HULIS and MP to the total BrC absorption are higher than their mass proportions to organic carbon mass, indicating that HULIS and MP are the main light-absorbing components in water-soluble and water-insoluble organic carbon fractions, respectively. With decreases in non-fossil HULIS, MP, and LP carbon fractions (66 ± 2%, 52 ± 2%, and 36 ± 3%, respectively), the abundances of unsaturated compounds and mass absorption efficiency at 365 nm of three fractions decreased synchronously. Increases in both non-fossil carbon and levoglucosan in winter imply that the enhanced light-absorption could be attributed to elevated levels of biomass burning organic aerosols (BBOA), which increases the number of light-absorbing nitrogen-containing compounds. Moreover, the major type of potential BrC in HULIS and MP carbon fractions are oxidized BBOA, but the potential BrC chromophores in LP are mainly associated with primary BBOA. This study reveals that biomass burning has adverse effects on radiative forcing and air quality, and probably indicates the significant influences of atmospheric oxidation reactions on the forms of chromophores. [ABSTRACT FROM AUTHOR]

Optical complexity and various properties of Case 2 waters make it essential to derive inherent optical properties (IOPs) through an appropriate method. Based on field measured data of Lake Chaohu between 2009 and 2018, the quasi-analytical algorithm (QAA) was modified for the particular scenario of that lake to derive absorption coefficients based on the moderate-resolution imaging spectroradiometer (MODIS) bands. By changing the reference wavelength to longer ones and building a relationship between the value of spectral power for particle backscattering coefficient (Y), suspended particulate matter (SPM), and above-surface remote-sensing reflectance (Rrs), we improved the accuracy of the retrieval of total absorption coefficients. The absorption coefficients of gelbstoff and non-algal particulates (adg) and absorption coefficients of phytoplankton (aph) in Lake Chaohu were also derived by changing important parameters according to Lake Chaohu. The derived aph tend to be bigger than measured aph in this study, while derived adg tend to be smaller than measured data. We also used the corrected MODIS surface reflectance product (MOD09/MYD09) to calculate the aph(443), aph(645), and aph(678) by the model proposed in this study. It shows that in summer and autumn, aph tended to be higher in the northwestern part of Lake Chaohu, and were relatively lower in the spring and winter, which is similar to previous studies. Overall, our study provides an algorithm that is effectively used in the case of Lake Chaohu and applicable to the data obtained by MODIS, which can be used for further study to investigate the change law of absorption coefficients in long time series by applying MODIS data. [ABSTRACT FROM AUTHOR]