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Li Z.,Hubei Engineering University | Zhou H.,CAS Wuhan Institute of Rock and Soil Mechanics | Song Y.-Z.,National Ocean Technology Center | Zhang C.-Q.,CAS Wuhan Institute of Rock and Soil Mechanics | Hu Q.-Z.,Hubei Engineering University
Yantu Lixue/Rock and Soil Mechanics | Year: 2013

Chlorite schist is a kind of soft rocks, and its large deformation and collapse due to excavation are greatly harmful to engineering safety. In order to investigate the mechanical property of chlorite schist, triaxial compression test is conducted and a new internal variable is defined considering the influence of stress state on plasticity evolution. According to test results, evolution characteristics of cohesion and friction angle are that the cohesion decreases firstly approximately linearly and then parabolically, but friction angle always decreases approximately parabolically. Meanwhile, based on test data, evolution of dilatancy angle is opposite to that of friction angle. Finally, mechanical model of chlorite schist is proposed considering hardening-softening and dilatancy characteristics; and then it is applied to simulate the triaxial test; the result shows a good agreement with the test data. Effort of this paper offers a rational mechanical model for engineering safety estimation and an important reference for the mechanical investigation of other similar soft rocks.

Zhang H.,National Ocean Technology Center | Zhang M.,Tsinghua University
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2013

In this paper, total harmonic distortion (THD) of phase generated carrier demodulation algorithm by digital arctangent approach (PGC-DAT algorithm) is analyzed. THD due to the deviations of modulation depth and carrier phase delay is investigated both theoretically and experimentally. The analytical expression of THD as the function of carrier modulation depth, signal amplitude, initial phase and deviations of modulation depth and carrier phase delay has been derived. According to our analysis, the maximum THD for different initial phases exists, which reaches the peak value when the signal amplitude is close to 1.2 rad. The best modulation depth to minimize the maximum THD is 2 rad. Finally, an experimental system is set up with the mean THD below -60 dB. The analytical expression of THD derived in this paper agrees well with the experimental results. © 2013 Copyright SPIE.

Chen J.,Ocean University of China | Chen J.,CAS Qingdao Institute of Oceanology | Cui T.,State Oceanic Administration | Tang J.,National Ocean Technology Center | Song Q.,National Satellite Ocean Application Service
Remote Sensing of Environment | Year: 2014

The objectives of this study are to evaluate the applicability of three existing retrieval algorithms of diffuse attenuation coefficients of downwelling irradiance at 490nm, Kd(490), for turbid Case II waters, and to improve these existing models using a simple semi-analytical (SSA) model. In this study, based on comparison of the Kd(490) predicted by these models with field measurements taken in the Bohai Sea and Yellow Sea, it is shown that the SSA model provides a stronger performance than these three selected existing models. The atmospheric influences on the MODIS data are removed using an improved shortwave infrared band-based (ISWIR-based) model, which is capable of retrieving spectral remote sensing reflectance within 19% uncertainty. The Kd(490) data was quantified from the MODIS images after atmospheric correction using the SSA model and Wang's model. The study results indicate that the SSA model produces 31.51% uncertainty in deriving Kd(490) from MODIS data, which is 12.1% higher than Wang's model. This study demonstrates the potential of the SSA model in estimating Kd(490) even in highly turbid coastal waters. © 2013 Elsevier Inc.

Sun X.J.,National Ocean Technology Center | Shi J.,Tianjin Institute of Urban Construction | Yang Y.,Tianjin Institute of Urban Construction
Advanced Materials Research | Year: 2013

Attitude control in three-dimensional space for AUV (autonomous underwater vehicle) with x-shaped fins is complicated but advantageous. Yaw, pitch and roll angles of the vehicle are all associated with deflection angle of each fin while navigating underwater. In this paper, a spatial motion mathematic model of the vehicle is built by using theorem of momentum and angular momentum, and the hydrodynamic forces acting on x-shaped fins and three-blade propeller are investigated to clarify complex principle of the vehicle motion. In addition, the nonlinear dynamics equation which indicates the coupling relationship between attitude angles of vehicle and rotation angles of x-shaped fins is derived by detailed deduction. Moreover, a decoupling controller based on artificial neural networks is developed to address the coupling issue exposed in attitude control. The neural networks based controller periodically calculates and outputs deflection angles of fins according to the attitude angles measured with magnetic compass, thus the vehicle's orientation can be maintained. By on-line training, twenty four weights in this controller converged according to index function. © (2013) Trans Tech Publications, Switzerland.

Zhang M.,CAS Institute of Remote Sensing | Tang J.,National Ocean Technology Center | Dong Q.,CAS Institute of Remote Sensing | Duan H.,CAS Nanjing Institute of Geography and Limnology | Shen Q.,CAS Institute of Remote Sensing
Optics Express | Year: 2014

We have presented an atmospheric correction algorithm for HJ-1 CCD imagery over Lakes Taihu and Chaohu with highly turbid waters. The Rayleigh scattering radiance (Lr) is calculated using the hyperspectral Lr with a wavelength interval 1nm. The hyperspectral Lr is interpolated from Lr in the central wavelengths of MODIS bands, which are converted from the band response-averaged Lr calculated using the Rayleigh look up tables (LUTs) in SeaDAS6.1. The scattering radiance due to aerosol (La) is interpolated from La at MODIS band 869nm, which is derived from MODIS imagery using a shortwave infrared atmospheric correction scheme. The accuracy of the atmospheric correction algorithm is firstly evaluated by comparing the CCD measured remote sensing reflectance (Rrs) with MODIS measurements, which are validated by the in situ data. The CCD measured Rrs is further validated by the in situ data for a total of 30 observation stations within ± 1h time window of satellite overpass and field measurements. The validation shows the mean relative errors about 0.341, 0.259, 0.293 and 0.803 at blue, green, red and near infrared bands. © 2014 Optical Society of America.

Zhang M.,Chinese Academy of Sciences | Tang J.,National Ocean Technology Center | Tang J.,CAS Institute of Remote Sensing Applications | Song Q.,National Satellite Ocean Application Service | Dong Q.,Chinese Academy of Sciences
Journal of Geophysical Research: Oceans | Year: 2010

Using in situ optical measurements collected during the 2003 spring cruise over the Yellow and East China seas, the particle backscattering ratio is calculated and spectral variability is analyzed by means of geometric mean regression. The analysis shows that the particle backscattering ratio can be regarded as wavelength-independent in the range of 442-676 nm, given the measurement uncertainties associated with the backscattering and scattering data. The backscattering ratio and attenuation measurements are used to calculate the particle refractive index, which is related to the particle composition. The distributions of the particle refractive index and the water component concentration along two transects suggest the feasibility for studying the particle composition. Copyright 2010 by the American Geophysical Union.

Xu W.,National Ocean Technology Center | Li F.,National Ocean Technology Center | Xia D.,National Ocean Technology Center
Ocean and Coastal Management | Year: 2014

China government attaches great importance to the ocean energy development (OED) industry and, in national planning, lists it as a strategic emerging industry, and the ocean energy development is under rapid growth in China. Estimated on basis of relevant OED plans, there will be massive sea area used for OED projects although their potential effects remain undefined, especially those negative impacts on marine ecological environment and other marine activities. Therefore, prior to the upsurge of OED, China government has carried out instructive exploration and trials on the method and mode of OED sea use management, on basis of the features of such sea use in China and relying on the existing marine resources management system. After summary of OED status, this paper makes analysis on the characteristics, trends and existing problems of such sea use in China, introduces the efforts of China government in regulating and managing such sea use through marine functional zoning planning, industry-purposed sea use planning, feasibility assessment of sea area use, environmental impact assessment of marine engineering and so on, and elaborates the future mode and prospect of OED sea use management in China. The research results show that it is rather necessary to, prior to deployment of large-scale OED development activities, consider and demonstrate the rationality and feasibility of the sea use in OED projects regarding such four aspects as the protection of marine ecological environment, the improvement of efficiency of sea area development and utilization, the coordination of sea use contradictions between industries, and the control of scale of sea area used. © 2013 Elsevier Ltd.

Wang Y.,National Ocean Technology Center | Yang N.,National Ocean Technology Center | Gao Y.-B.,National Ocean Technology Center
OCEANS 2016 - Shanghai | Year: 2016

Seawater chlorophyll - A (Chla) represents algal biomass in ocean and is a major index of eutrophication. In this paper, bootstrapped artificial neural network (BANN) model is developed for predicting the seawater Chla concentration around the north Pacific Rim. Three-layer ANN structure is applied and the modeling is based on comprehensive five-minute interval datasets of water temperature, depth, salinity and Chla collected by Continuous Plankton Recorder Survey of north Pacific in 2014. Prediction intervals (PI) are constructed according to the calculated uncertainties from the model structure and data noise. The performance of BANN is compared with traditional ANN model. The results show that BANN with 6 hidden neurons can forecast Chla effectively and produce better performance than ANN model when the bootstrapped number are bigger than 20. In addition, mean relative error (MRE) and root mean square error (RMSE) of the BANN(20) are respective 8.57% and 1.869 mg/m3, but the BANN is not fit for the Alaska coastal region. About 52 (1.31%) observations are larger than the upper bound of prediction intervals and these 'outliers' fallen into three regions can be attributed to potential nutrients from mariculture or terrestrial influences which are inferred as anthropogenic and natural sources. The BANN model applied in this paper can help managers to make more appropriate decisions on ocean ecological management. © 2016 IEEE.

Zhang M.,Chinese Academy of Sciences | Tang J.,National Ocean Technology Center | Dong Q.,Chinese Academy of Sciences | Song Q.,State Oceanic Administration
IEEE Transactions on Geoscience and Remote Sensing | Year: 2013

A forward Monte Carlo 3-D (FMC3D) model is developed for simulating light fields in a volume of water where the boundary conditions for radiance values can be expressed by mathematical formulas, which cannot be done using the radiative transfer models currently available such as HydroLight. Water is assumed parallel homogenous for these models, which are incapable of investigating the sidewall reflectance effect on the light fields. These ones are called quasi-3-D radiative transfer models. The FMC3D model perfects the assumption and the incapability and is validated using the in situ data measured in the tank experiment. The FMC3D model is first applied to investigate the sidewall reflectance effect on the remote sensing reflectance R\rm rs for waters in a fabricated tank with infinite depth and different radii. The investigation shows that the effect is decreasing with the increase in the tank radius and that the minimum radius that the effect is negligible for highly scattering water is bigger than that for highly absorbing water. Taking the tank used in the experiment carried out in a previous work by Han and Rundquist as an example, the FMC3D model is second applied to investigate the combining effects on Rrs from bottom and sidewall reflectances. Compared with Rrs for open water, the Rrs for tank water having the same inherent optical properties is underestimated. The underestimation is increasing with the increase in the single scattering albedo ω and can be up to 32% for water with ω = 0.88, showing that the effects cannot be removed by the black inside wall, which is a method commonly used in tank experiments. The potential applications of the FMC3D model are discussed, taking the examples of the correction for the wall reflectance effect on apparent spectra measured in tank experiments and of the scattering error correction for the reflective tube absorption coefficient measured using a WET Labs AC-9 or AC-S device. © 2012 IEEE.

Zhang M.,Chinese Academy of Sciences | Tang J.,National Ocean Technology Center | Dong Q.,Chinese Academy of Sciences | Song Q.,National Satellite Ocean Application Service | Ding J.,National Satellite Ocean Application Service
Remote Sensing of Environment | Year: 2010

A retrieval algorithm, of total suspended matter (TSM) concentration in the Yellow Sea (YS) and East China Sea (ECS) was developed using observations made in the 2003 Spring and Autumn cruises over the YS and the ECS. Analysis of the in-situ backscattering coefficients of the suspended particles (bbp) indicates that the accuracy becomes worse when the concentration of TSM (CTSM) is higher than 20 mg/l. The accuracy of the bbp is improved by using a bio-optical model in which bbp is optimized with a non-linear least-square Levenberg-Marquardt method. The remote sensing reflectance (Rrs) is obtained by means of the optimization. The optimized Rrs for waters with CTSM higher than 20 mg/l, together with the measured Rrs for waters with CTSM lower than 20 mg/l, are used to establish the relationships between Rrs(748), Rrs(869) and Rrs(645), which are used in the iterative method for atmospheric correction. Two atmospheric correction algorithms are switched according to the water turbidity. The shortwave infrared wavelengths (SWIR) method is used for waters with high-turbidity, and the iterative method is used otherwise. Results of the atmospheric correction were then applied to the Tassan model modified in this paper to compute the CTSM. Comparison between the retrieval results from MODIS imagery and the in-situ measurements indicates that the algorithms described in this paper can provide a reliable estimation of the CTSM distributions in the YS and ECS. © 2009 Elsevier Inc. All rights reserved.

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