An accurate Modulation Transfer Function(MTF)is essential for Synthetic Aperture Radar(SAR)wave spectra retrieval.This study aimed to investigate the performance of a quad-polarized wave retrieval algorithm based on f...An accurate Modulation Transfer Function(MTF)is essential for Synthetic Aperture Radar(SAR)wave spectra retrieval.This study aimed to investigate the performance of a quad-polarized wave retrieval algorithm based on fully polarimetric SAR image data using the improved tilt MTF and considering the influence of wind speed.The tilt MTF is the key factor in the wave retrieval scheme from quad-polarized(Vertical-Vertical(VV),Horizontal-Horizontal(HH),Vertical-Horizontal(VH),and Horizontal-Vertical(HV))SAR images.In this study,the waves were inverted from more than 1300 Gaofen-3(GF-3)images acquired in quad-polarization strip mode with a spatial resolution of 16 m and a swath coverage of 50 km.The winds were retrieved using the Geophysical Model Function(GMF)C-band SAR model for Gaofen-3(CSARMOD-GF),which is suitable for re-calibrated GF-3 images in VV-polarization.The comparison of the wind speed yielded a Root Mean Square Error(RMSE)of 1.73 m/s and a Correlation Coefficient(COR)of 0.94.The validation of the Significant Wave Height(SWH)simulated using the Waves Nearshore(SWAN)model against Haiyang-2B(HY-2B)altimeter data yielded an RMSE of 0.56 m and a COR of 0.87.The results reveal that the SAR-derived wind and SWAN-simulated SWH are suitable for analysis of SAR wave retrieval.The full polarimetric technique was applied to the collected images,and the statistical analysis yielded a RMSE of 0.51 m,a COR of 0.75,and a Scatter Index(SI)of 0.44 compared with the SWHs retrieved using the simulations from the SWAN model.The non-polarized contribution in the Normalized Radar Cross Section(NRCS;unit:dB)caused by wave breaking σ_(0)^(wb) was calculated using a theoretical approach that employs the VV-polarized calibrated NRCS σ_(0)^(vv) and HH-polarized calibrated NRCS.The effect of wave breaking on the SAR retrieval waves was studied.The bias(SAR-derived minus SWAN-simulated SWH)increased as the(σ_(0)^(wb)/σ_(0)^(vv))ratio(>0.4)increased,and the accuracy improved when the ratio was less than 0.4.This behavior is reasonable since the wave breaking inevitably affects the tilt modulation.Therefore,wave breaking should be considered in SAR wave retrieval using the approach proposed in this paper under extreme sea states,such as typhoons and hurricanes.展开更多
The CBR (Case-Based Reasoning) usually is been used to accomplish customized products by variant design or reusable design.In the CBR,retrieve is very important.A simple case retrieval method is been brought forward t...The CBR (Case-Based Reasoning) usually is been used to accomplish customized products by variant design or reusable design.In the CBR,retrieve is very important.A simple case retrieval method is been brought forward to retrieve a opti- mal prototype based on using inputted multi-parameters,it can be programmed easily.An example has been proved this method can find optimal prototype for new design task efficiently.展开更多
Many synthetic aperture radar (SAR) wave height retrieval algorithms have been developed.However,the wave height retrievals from most existing methods either depend on other input as the first guess or are restricted ...Many synthetic aperture radar (SAR) wave height retrieval algorithms have been developed.However,the wave height retrievals from most existing methods either depend on other input as the first guess or are restricted to the long wave regime.A semiempirical algorithm is presented,which has the objective to estimate the wave height from SAR imagery without any prior knowledge.The proposed novel algorithm was developed based on the theoretical SAR ocean wave imaging mechanism and the empirical relation between two types of wave period.The dependency of the proposed model on radar incident and wave direction was analyzed.For Envisat advanced synthetic aperture radar (ASAR) wave mode data,the model can be reduced to the simple form with two input parameters,i.e.,the cutoff wavelength and peak wavelength of ocean wave,which can be retrieved from SAR imagery without any prior knowledge of wind or wave.Using Envisat ASAR wave mode data and the collocated buoy measurements from NDBC,the scmicmpirical algorithm is validated and compared with the Envisat ASAR level 2 products.The root-mean-square-error (RMSE) and scatter index (SI) in respect to the in situ measurements are 0.52 m and 19％ respectively.Validation results indicate that,for Envisat ASAR wave mode data,the proposed method works well.展开更多
The goal of this study was to investigate the performance of a spectral-transformation wave retrieval algorithm and confirm the accuracy of wave retrieval from C-band Chinese Gaofen-3(GF-3)Synthetic Aperture Radar(SAR...The goal of this study was to investigate the performance of a spectral-transformation wave retrieval algorithm and confirm the accuracy of wave retrieval from C-band Chinese Gaofen-3(GF-3)Synthetic Aperture Radar(SAR)images.More than 200 GF-3 SAR images of the coastal China Sea and the Japan Sea for dates from January to July 2020 were acquired in the Quad-Polarization Strip(QPS)mode.The images had a swath of 30 km and a spatial resolution of 8 m pixel size.They were processed to retrieve Significant Wave Height(SWH),which is simulated from a numerical wave model called Simulating WAves Nearshore(SWAN).The first-guess spectrum is essential to the accuracy of Synthetic Aperture Radar(SAR)wave spectrum retrieval.Therefore,we proposed a wave retrieval scheme combining the theocratic-based Max Planck Institute Algorithm(MPI),a Semi-Parametric Retrieval Algorithm(SPRA),and the Parameterized First-guess Spectrum Method(PFSM),in which a full wave-number spectrum and a non-empirical ocean spectrum proposed by Elfouhaily are applied.The PFSM can be driven using the wind speed without calculating the dominant wave phase speed.Wind speeds were retrieved using a Vertical-Vertical(VV)polarized geophysical model function C-SARMOD2.The proposed algorithm was implemented for all collected SAR images.A comparison of SAR-derived wind speeds with European Center for Medium-Range Weather Forecasts(ECMWF)ERA-5 data showed a 1.95 m/s Root-Mean-Squared Error(RMSE).The comparison of retrieved SWH with SWAN-simulated results demonstrated a 0.47 m RMSE,which is less than the 0.68 m RMSE of SWH when using the PFSM algorithm.展开更多
To obtain the interaction characteristics between Internal solitary waves(ISWs)and submerged bodies,a three-dimensional numerical model for simulating ISWs was established in the present study based on the RANS equati...To obtain the interaction characteristics between Internal solitary waves(ISWs)and submerged bodies,a three-dimensional numerical model for simulating ISWs was established in the present study based on the RANS equation.The velocity entrance method was adopted to generate the ISWs.First,the reliability of this numerical model was validated by comparing it with theoretical and literature results.Then,the influence of environmental and navigation parameters on interactions between ISWs and a fixed SUBOFF-submerged body was studied.According to research,the hydrodynamic performance of the submerged body has been significantly impacted by the ISWs when the body is nearing the central region of the wave.Besides,the pitching moment(y')will predominate when the body encounters the ISWs at a certain angle between 0°and 180°,and the lateral force is larger than the horizontal force.Additionally,the magnitude of the force acting on the body is mostly affected by the wave amplitude.The variation of the vertical force is the main way that ISWs affect the hydrodynamic performance of the bodies.The investigations and findings discussed above can serve as a guide to forecast how ISWs will interact with submerged bodies.展开更多
Satellite hyperspectral infrared sounder measurements have better horizontal resolution than other sounding techniques as it boasts the stratospheric gravity wave(GW)analysis.To accurately and efficiently derive the t...Satellite hyperspectral infrared sounder measurements have better horizontal resolution than other sounding techniques as it boasts the stratospheric gravity wave(GW)analysis.To accurately and efficiently derive the three-dimensional structure of the stratospheric GWs from the single-field-of-view(SFOV)Atmospheric Infra Red Sounder(AIRS)observations,this paper firstly focuses on the retrieval of the atmospheric temperature profiles in the altitude range of 20-60 km with an artificial neural network approach(ANN).The simulation experiments show that the retrieval bias is less than 0.5 K,and the root mean square error(RMSE)ranges from 1.8 to 4 K.Moreover,the retrieval results from 20 granules of the AIRS observations with the trained neural network(AIRS_SFOV)and the corresponding operational AIRS products(AIRS_L2)as well as the dual-regression results from the Cooperative Institute for Meteorological Satellite Studies(CIMSS)(AIRS_DR)are compared respectively with ECMWF T799 data.The comparison indicates that the standard deviation of the ANN retrieval errors is significantly less than that of the AIRS_DR.Furthermore,the analysis of the typical GW events induced by the mountain Andes and the typhoon"Soulik"using different data indicates that the AIRS_SFOV results capture more details of the stratospheric gravity waves in the perturbation amplitude and pattern than the operational AIRS products do.展开更多
In this paper, without recourse to the nonlinear dynamical equations of the waves, the nonlinear random waves are retrieved from the non-Gaussian characteristic of the sea surface elevation distribution. The question ...In this paper, without recourse to the nonlinear dynamical equations of the waves, the nonlinear random waves are retrieved from the non-Gaussian characteristic of the sea surface elevation distribution. The question of coincidence of the nonlinear wave profile, spectrum and its distributions of maximum (or minimum) values of the sea surface elevation with results derived from some existing nonlinear theories is expounded under the narrow-band spectrum condition. Taking the shoaling sea wave as an example, the nonlinear random wave process and its spectrum in shallow water are retrieved from both the non-Gaussian characteristics of the sea surface elevation distribution in shallow water and the normal sea waves in deep water and compared with the values actually measured. Results show that they can coincide with the actually measured values quite well, thus, this can confirm that the method proposed in this paper is feasible.展开更多
The parameter reconstruction of strong-scattering media is a challenge for conventional full waveform inversion(FWI).Direct envelope inversion(DEI)is an effective method for large-scale and strongscattering structures...The parameter reconstruction of strong-scattering media is a challenge for conventional full waveform inversion(FWI).Direct envelope inversion(DEI)is an effective method for large-scale and strongscattering structures imaging without the need of low-frequency seismic data.However,the current DEI methods are all based on the acoustic approximation.Whereas,in real cases,seismic records are the combined effects of the subsurface multi-parameters.Therefore,the study of DEI in elastic media is necessary for the accurate inversion of strong-scattering structures,such as salt domes.In this paper,we propose an elastic direct envelope inversion(EDEI)method based on wave mode decomposition.We define the objective function of EDEI using multi-component seismic data and derive its gradient formulation.To reduce the coupling effects of multi-parameters,we introduce the wave mode decomposition method into the gradient calculation of EDEI.The update of Vp is primarily the contributions of decomposed P-waves.Two approaches on Vs gradient calculation are proposed,i.e.using the petrophysical relation and wave mode decomposition method.Finally,we test the proposed method on a layered salt model and the SEG/EAGE salt model.The results show that the proposed EDEI method can reconstruct reliable large-scale Vp and Vs models of strong-scattering salt structures.The successive elastic FWI can obtain high-precision inversion results of the strong-scattering salt model.The proposed method also has a good anti-noise performance in the moderate noise level.展开更多
The multi-parameter inverse scattering problem of elastic waveequation with single fre- quency is investigated within Bornapproximation. By use of a wideband measuring scheme in which bothtransmitters and receivers sc...The multi-parameter inverse scattering problem of elastic waveequation with single fre- quency is investigated within Bornapproximation. By use of a wideband measuring scheme in which bothtransmitters and receivers scan over the half-space surface, theformula of the scattering field of elastic wave is derived. Fourtypes of mode conversion of elastic wave(P→P, P→S, S→P, S→S)areseparated from the scattering field. These components containsufficient information for usto recon- struct the configuration ofthe density and Lame parameters of the medium.展开更多
A method to retrieve ocean wave spectra from SAR images, named Parameterized First-guess Spectrum Method （PFSM）, was proposed after interpretation of the theory to ocean wave imaging and analysis of the drawbacks of...A method to retrieve ocean wave spectra from SAR images, named Parameterized First-guess Spectrum Method （PFSM）, was proposed after interpretation of the theory to ocean wave imaging and analysis of the drawbacks of the retrieving model generally used. In this method, with additional information and satellite parameters, the separating wave-number is first calculated to determine the maximum wave-number beyond which the linear relation can be used. The separating wave-number can be calculated using the additional information on wind velocity and parameters of SAR satellite. And then the SAR spectrum can be divided into SAR spectrum of wind wave and of swell according to the result of separating wave-number. The portion of SAR spectrum generated by wind wave, is used to search for the most suitable parameters of ocean wind wave spectrum, including propagation direction of ocean wave, phase speed of dominating wave and the angle spreading coefficient. The swell spectrum is acquired by directly inversing the linear relation of ocean wave spectrum to SAR spectrum given the portion of SAR spectrum generated by swell. We used the proposed method to retrieve the ocean wave spectrum from ERS-SAR data from the South China Sea and compared the result with altimeter data. The agreement indicates that the PFSM is reliable.展开更多
ICESat-2(Ice,Cloud and Land Elevation Satellite 2)卫星激光雷达数据被广泛应用于地形地貌测绘、森林监测、水域监测等多个领域。当ICESat-2飞越海面时,可以检测到被海面反射回的微弱光子信号,其反映了海面的起伏状态,但同时也包含...ICESat-2(Ice,Cloud and Land Elevation Satellite 2)卫星激光雷达数据被广泛应用于地形地貌测绘、森林监测、水域监测等多个领域。当ICESat-2飞越海面时,可以检测到被海面反射回的微弱光子信号,其反映了海面的起伏状态,但同时也包含了设备噪声、大气颗粒散射噪声、背景干扰噪声等大量噪声光子。本研究提出了一种新的海面信号光子提取和海浪要素反演方法,首先将原始ICESat-2数据沿垂直方向均匀分段,统计各段内光子数,对其进行高斯拟合和迭代中值滤波,确定精确的海面光子上下界,从而提取出海面信号光子。进一步采用支持向量回归拟合,提取瞬时海面轮廓。在此基础上,利用频谱分析方法计算出有效波高和初步海浪峰值波长,通过对同步的强弱激光束相位相干分析,估算海浪波向,并修正海浪峰值波长和计算海浪峰值周期。对来自好望角和萨摩亚海域的24条轨道ICESat-2数据进行海面光子提取和海浪要素反演,并将结果与ERA5再分析数据进行对比验证。结果表明,海浪有效波高、波向和峰值周期的均方根误差(RMSE)分别为0.12 m、28.58°和0.48 s,表明该方法具有较高的海浪要素反演精度,具备进一步探索更大范围激光雷达数据海浪要素提取和分析的潜力。展开更多
This paper proposes the retrieval method of ocean wave spectrum for airborne radar observations at small incidence angles, which is slightly modified from the method developed by Hauser. Firstly, it makes use of integ...This paper proposes the retrieval method of ocean wave spectrum for airborne radar observations at small incidence angles, which is slightly modified from the method developed by Hauser. Firstly, it makes use of integration method to estimate total mean square slope instead of fitting method, which aims to reduce the affects of fluctuations superposed on normalized radar cross-section by integration. Secondly, for eliminating the noise spectrum contained in signal spectrum, the method considers the signal spectrum in certain look direction without any long wave components as the assumed noise spectrum, which would be subtracted from signal spectrum in any look direction for linear wave spectrum retrieval. Estimated v from the integration method are lower than the one from fitting method and have a standard deviation of 0.004 between them approximately. The assumed noise spectrum energy almost has no big variations along with the wave number and is slightly lower to the high wave number part of signal spectrum in any look direction, which follows that the assumption makes sense. The retrieved directional spectra are compared with the buoy records in terms of peak wavelength, peak direction and the significant wave height. Comparisons show that the retrieved peak wavelength and significant wave height are slightly higher than the buoy records but don＇t differs significantly （error less than 10%）. For peak direction, the swell waves in first case basically propagate in the wind direction 6 hours ago and the wind-generated waves in second case also propagate in the wind direction, but the 180° ambiguity remains. Results show that the modified method can carry out the retrieval of directional wave spectrum.展开更多
We explore the general characteristics of a matter-wave Sagnac interferometer in a two-parameter estimation scheme. We find that the measurement precisions of both parameters cannot reach the Heisenberg limit(HL) simu...We explore the general characteristics of a matter-wave Sagnac interferometer in a two-parameter estimation scheme. We find that the measurement precisions of both parameters cannot reach the Heisenberg limit(HL) simultaneously when the input state is maximally entangled. Only one of the parameters' uncertainties can approach the HL while the other is scaled by the standard quantum limit.We provide the conditions with which the measurement precision of the specific parameter can reach the HL. We also discuss and figure out the concrete expressions of the constraint conditions for saturating the quantum Cramér–Rao bound. To satisfy these constraint conditions, the evolution time has to be a series of discrete values. Additionally, we calculate the variances of the parameters through some examples under these constraint conditions. The results provided in our work show some intrinsic features of the matter-wave Sagnac interferometer for the two-parameter estimation, which can be valuable in actual experiments.展开更多
Based on oceanic internal wave SAR imaging mechanism and the microwave scattering imaging model for oceanic surface features, we developed a new method to extract internal wave parameters from SAR imagery. Firstly, th...Based on oceanic internal wave SAR imaging mechanism and the microwave scattering imaging model for oceanic surface features, we developed a new method to extract internal wave parameters from SAR imagery. Firstly, the initial wind fields are derived from NCEP reanalysis data, the sea water density and oceanic internal wave pycnocline depth are estimated from the Levites data, the surface currents induced by the internal wave are calculated according to the KDV equation. The NRCS profile is then simulated by solving the action balance equation and using the sea surface radar backscatter model. Both the winds and internal wave pycnocline depth are adjusted by using the dichotomy method step by step to make the simulated data approach the SAR image. Then, the wind speed, pycnocline depth, the phase speed, the group velocity and the amplitude of internal wave can be retrieved from SAR imagery when a best fit between simulated signals and the SAR image appears. The method is tested on one scene SAR image near Dongsha Island, in the South China Sea, results show that the simulated oceanic internal wave NRCS profile is in good agreement with that on the SAR image with the correlation coefficient as high as 90%, and the amplitude of oceanic internal wave retrieved from the SAR imagery is comparable with the SODA data. Besides, the phase speeds retrieved from other 16 scene SAR images in the South China Sea are in good agreement with the empirical formula which describes the relations between internal wave phase speed and water depths, both the root mean square and relative error are less than O. 11 m.s 1 and 7%, respectively, indicating that SAR images are useful for internal wave parameters retrieval and the method developed in this paper is convergent and applicable.展开更多
基金partially supported by the National Natural Science Foundation of China[grant number 42076238]the Natural Science Foundation of Shanghai[grant number 23ZR1426900].
文摘An accurate Modulation Transfer Function(MTF)is essential for Synthetic Aperture Radar(SAR)wave spectra retrieval.This study aimed to investigate the performance of a quad-polarized wave retrieval algorithm based on fully polarimetric SAR image data using the improved tilt MTF and considering the influence of wind speed.The tilt MTF is the key factor in the wave retrieval scheme from quad-polarized(Vertical-Vertical(VV),Horizontal-Horizontal(HH),Vertical-Horizontal(VH),and Horizontal-Vertical(HV))SAR images.In this study,the waves were inverted from more than 1300 Gaofen-3(GF-3)images acquired in quad-polarization strip mode with a spatial resolution of 16 m and a swath coverage of 50 km.The winds were retrieved using the Geophysical Model Function(GMF)C-band SAR model for Gaofen-3(CSARMOD-GF),which is suitable for re-calibrated GF-3 images in VV-polarization.The comparison of the wind speed yielded a Root Mean Square Error(RMSE)of 1.73 m/s and a Correlation Coefficient(COR)of 0.94.The validation of the Significant Wave Height(SWH)simulated using the Waves Nearshore(SWAN)model against Haiyang-2B(HY-2B)altimeter data yielded an RMSE of 0.56 m and a COR of 0.87.The results reveal that the SAR-derived wind and SWAN-simulated SWH are suitable for analysis of SAR wave retrieval.The full polarimetric technique was applied to the collected images,and the statistical analysis yielded a RMSE of 0.51 m,a COR of 0.75,and a Scatter Index(SI)of 0.44 compared with the SWHs retrieved using the simulations from the SWAN model.The non-polarized contribution in the Normalized Radar Cross Section(NRCS;unit:dB)caused by wave breaking σ_(0)^(wb) was calculated using a theoretical approach that employs the VV-polarized calibrated NRCS σ_(0)^(vv) and HH-polarized calibrated NRCS.The effect of wave breaking on the SAR retrieval waves was studied.The bias(SAR-derived minus SWAN-simulated SWH)increased as the(σ_(0)^(wb)/σ_(0)^(vv))ratio(>0.4)increased,and the accuracy improved when the ratio was less than 0.4.This behavior is reasonable since the wave breaking inevitably affects the tilt modulation.Therefore,wave breaking should be considered in SAR wave retrieval using the approach proposed in this paper under extreme sea states,such as typhoons and hurricanes.
基金Funded by the Scientific Foundation of Shanghai Automobile Industry(No.0212).
文摘The CBR (Case-Based Reasoning) usually is been used to accomplish customized products by variant design or reusable design.In the CBR,retrieve is very important.A simple case retrieval method is been brought forward to retrieve a opti- mal prototype based on using inputted multi-parameters,it can be programmed easily.An example has been proved this method can find optimal prototype for new design task efficiently.
基金The Ocean Science Youth Fund of State Oceanic Administration of China under contract No.2010418the fund of State Administration for Science,Technology and Industry for National Defensethe Open Fund of State Key Laboratory of Satellite Ocean Environment Dynamics,Second Institute of Oceanography,State Oceanic Administration of China under contract No.SOED1010
文摘Many synthetic aperture radar (SAR) wave height retrieval algorithms have been developed.However,the wave height retrievals from most existing methods either depend on other input as the first guess or are restricted to the long wave regime.A semiempirical algorithm is presented,which has the objective to estimate the wave height from SAR imagery without any prior knowledge.The proposed novel algorithm was developed based on the theoretical SAR ocean wave imaging mechanism and the empirical relation between two types of wave period.The dependency of the proposed model on radar incident and wave direction was analyzed.For Envisat advanced synthetic aperture radar (ASAR) wave mode data,the model can be reduced to the simple form with two input parameters,i.e.,the cutoff wavelength and peak wavelength of ocean wave,which can be retrieved from SAR imagery without any prior knowledge of wind or wave.Using Envisat ASAR wave mode data and the collocated buoy measurements from NDBC,the scmicmpirical algorithm is validated and compared with the Envisat ASAR level 2 products.The root-mean-square-error (RMSE) and scatter index (SI) in respect to the in situ measurements are 0.52 m and 19％ respectively.Validation results indicate that,for Envisat ASAR wave mode data,the proposed method works well.
基金supported by the Key Special Project for Introduced Talents Team of the Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)[Grant No GML2019ZD0302]the National Natural Science Foundation of China[Grant Nos 41806005 and 42076238]the China Postdoctoral Science Foundation[Grant No 2020M670245].
文摘The goal of this study was to investigate the performance of a spectral-transformation wave retrieval algorithm and confirm the accuracy of wave retrieval from C-band Chinese Gaofen-3(GF-3)Synthetic Aperture Radar(SAR)images.More than 200 GF-3 SAR images of the coastal China Sea and the Japan Sea for dates from January to July 2020 were acquired in the Quad-Polarization Strip(QPS)mode.The images had a swath of 30 km and a spatial resolution of 8 m pixel size.They were processed to retrieve Significant Wave Height(SWH),which is simulated from a numerical wave model called Simulating WAves Nearshore(SWAN).The first-guess spectrum is essential to the accuracy of Synthetic Aperture Radar(SAR)wave spectrum retrieval.Therefore,we proposed a wave retrieval scheme combining the theocratic-based Max Planck Institute Algorithm(MPI),a Semi-Parametric Retrieval Algorithm(SPRA),and the Parameterized First-guess Spectrum Method(PFSM),in which a full wave-number spectrum and a non-empirical ocean spectrum proposed by Elfouhaily are applied.The PFSM can be driven using the wind speed without calculating the dominant wave phase speed.Wind speeds were retrieved using a Vertical-Vertical(VV)polarized geophysical model function C-SARMOD2.The proposed algorithm was implemented for all collected SAR images.A comparison of SAR-derived wind speeds with European Center for Medium-Range Weather Forecasts(ECMWF)ERA-5 data showed a 1.95 m/s Root-Mean-Squared Error(RMSE).The comparison of retrieved SWH with SWAN-simulated results demonstrated a 0.47 m RMSE,which is less than the 0.68 m RMSE of SWH when using the PFSM algorithm.
基金financially supported by the Shandong Province Taishan Scholars Project (Grant No.tsqn201909172)Fundamental Research Funds for the Central Universities (Grant No.HIT.OCEF.2021037)+1 种基金the University Young Innovational Team Program,Shandong Province (Grant No.2019KJB004)the China Scholarship Council (Grant No.202106120123)。
文摘To obtain the interaction characteristics between Internal solitary waves(ISWs)and submerged bodies,a three-dimensional numerical model for simulating ISWs was established in the present study based on the RANS equation.The velocity entrance method was adopted to generate the ISWs.First,the reliability of this numerical model was validated by comparing it with theoretical and literature results.Then,the influence of environmental and navigation parameters on interactions between ISWs and a fixed SUBOFF-submerged body was studied.According to research,the hydrodynamic performance of the submerged body has been significantly impacted by the ISWs when the body is nearing the central region of the wave.Besides,the pitching moment(y')will predominate when the body encounters the ISWs at a certain angle between 0°and 180°,and the lateral force is larger than the horizontal force.Additionally,the magnitude of the force acting on the body is mostly affected by the wave amplitude.The variation of the vertical force is the main way that ISWs affect the hydrodynamic performance of the bodies.The investigations and findings discussed above can serve as a guide to forecast how ISWs will interact with submerged bodies.
基金National Natural Science Foundation of China(41575031,41375024)Postdoctoral Science Foundation of China(2015M580124)Meteorology Research Special Funds for Public Welfare Projects(GYHY201406011)。
文摘Satellite hyperspectral infrared sounder measurements have better horizontal resolution than other sounding techniques as it boasts the stratospheric gravity wave(GW)analysis.To accurately and efficiently derive the three-dimensional structure of the stratospheric GWs from the single-field-of-view(SFOV)Atmospheric Infra Red Sounder(AIRS)observations,this paper firstly focuses on the retrieval of the atmospheric temperature profiles in the altitude range of 20-60 km with an artificial neural network approach(ANN).The simulation experiments show that the retrieval bias is less than 0.5 K,and the root mean square error(RMSE)ranges from 1.8 to 4 K.Moreover,the retrieval results from 20 granules of the AIRS observations with the trained neural network(AIRS_SFOV)and the corresponding operational AIRS products(AIRS_L2)as well as the dual-regression results from the Cooperative Institute for Meteorological Satellite Studies(CIMSS)(AIRS_DR)are compared respectively with ECMWF T799 data.The comparison indicates that the standard deviation of the ANN retrieval errors is significantly less than that of the AIRS_DR.Furthermore,the analysis of the typical GW events induced by the mountain Andes and the typhoon"Soulik"using different data indicates that the AIRS_SFOV results capture more details of the stratospheric gravity waves in the perturbation amplitude and pattern than the operational AIRS products do.
基金This work is funded by National Natural Science Foundation of China
文摘In this paper, without recourse to the nonlinear dynamical equations of the waves, the nonlinear random waves are retrieved from the non-Gaussian characteristic of the sea surface elevation distribution. The question of coincidence of the nonlinear wave profile, spectrum and its distributions of maximum (or minimum) values of the sea surface elevation with results derived from some existing nonlinear theories is expounded under the narrow-band spectrum condition. Taking the shoaling sea wave as an example, the nonlinear random wave process and its spectrum in shallow water are retrieved from both the non-Gaussian characteristics of the sea surface elevation distribution in shallow water and the normal sea waves in deep water and compared with the values actually measured. Results show that they can coincide with the actually measured values quite well, thus, this can confirm that the method proposed in this paper is feasible.
基金financial support jointly provided by the National Key R&D Program of China under contract number 2019YFC0605503Cthe Major Projects during the 14th Five-year Plan period under contract number 2021QNLM020001+2 种基金the National Outstanding Youth Science Foundation under contract number 41922028the Funds for Creative Research Groups of China under contract number 41821002the Major Projects of CNPC under contract number ZD2019-183-003。
文摘The parameter reconstruction of strong-scattering media is a challenge for conventional full waveform inversion(FWI).Direct envelope inversion(DEI)is an effective method for large-scale and strongscattering structures imaging without the need of low-frequency seismic data.However,the current DEI methods are all based on the acoustic approximation.Whereas,in real cases,seismic records are the combined effects of the subsurface multi-parameters.Therefore,the study of DEI in elastic media is necessary for the accurate inversion of strong-scattering structures,such as salt domes.In this paper,we propose an elastic direct envelope inversion(EDEI)method based on wave mode decomposition.We define the objective function of EDEI using multi-component seismic data and derive its gradient formulation.To reduce the coupling effects of multi-parameters,we introduce the wave mode decomposition method into the gradient calculation of EDEI.The update of Vp is primarily the contributions of decomposed P-waves.Two approaches on Vs gradient calculation are proposed,i.e.using the petrophysical relation and wave mode decomposition method.Finally,we test the proposed method on a layered salt model and the SEG/EAGE salt model.The results show that the proposed EDEI method can reconstruct reliable large-scale Vp and Vs models of strong-scattering salt structures.The successive elastic FWI can obtain high-precision inversion results of the strong-scattering salt model.The proposed method also has a good anti-noise performance in the moderate noise level.
基金Foundation of Ph.D Program of the State Education Commission of China
文摘The multi-parameter inverse scattering problem of elastic waveequation with single fre- quency is investigated within Bornapproximation. By use of a wideband measuring scheme in which bothtransmitters and receivers scan over the half-space surface, theformula of the scattering field of elastic wave is derived. Fourtypes of mode conversion of elastic wave(P→P, P→S, S→P, S→S)areseparated from the scattering field. These components containsufficient information for usto recon- struct the configuration ofthe density and Lame parameters of the medium.
基金Supported by the High-Tech Research and Development Program of China (863 Program, No. 2001AA633070 2003AA604040)the National Basic Research Program of China (973 Program. No. 2005CB422307)
文摘A method to retrieve ocean wave spectra from SAR images, named Parameterized First-guess Spectrum Method （PFSM）, was proposed after interpretation of the theory to ocean wave imaging and analysis of the drawbacks of the retrieving model generally used. In this method, with additional information and satellite parameters, the separating wave-number is first calculated to determine the maximum wave-number beyond which the linear relation can be used. The separating wave-number can be calculated using the additional information on wind velocity and parameters of SAR satellite. And then the SAR spectrum can be divided into SAR spectrum of wind wave and of swell according to the result of separating wave-number. The portion of SAR spectrum generated by wind wave, is used to search for the most suitable parameters of ocean wind wave spectrum, including propagation direction of ocean wave, phase speed of dominating wave and the angle spreading coefficient. The swell spectrum is acquired by directly inversing the linear relation of ocean wave spectrum to SAR spectrum given the portion of SAR spectrum generated by swell. We used the proposed method to retrieve the ocean wave spectrum from ERS-SAR data from the South China Sea and compared the result with altimeter data. The agreement indicates that the PFSM is reliable.
文摘ICESat-2(Ice,Cloud and Land Elevation Satellite 2)卫星激光雷达数据被广泛应用于地形地貌测绘、森林监测、水域监测等多个领域。当ICESat-2飞越海面时,可以检测到被海面反射回的微弱光子信号,其反映了海面的起伏状态,但同时也包含了设备噪声、大气颗粒散射噪声、背景干扰噪声等大量噪声光子。本研究提出了一种新的海面信号光子提取和海浪要素反演方法,首先将原始ICESat-2数据沿垂直方向均匀分段,统计各段内光子数,对其进行高斯拟合和迭代中值滤波,确定精确的海面光子上下界,从而提取出海面信号光子。进一步采用支持向量回归拟合,提取瞬时海面轮廓。在此基础上,利用频谱分析方法计算出有效波高和初步海浪峰值波长,通过对同步的强弱激光束相位相干分析,估算海浪波向,并修正海浪峰值波长和计算海浪峰值周期。对来自好望角和萨摩亚海域的24条轨道ICESat-2数据进行海面光子提取和海浪要素反演,并将结果与ERA5再分析数据进行对比验证。结果表明,海浪有效波高、波向和峰值周期的均方根误差(RMSE)分别为0.12 m、28.58°和0.48 s,表明该方法具有较高的海浪要素反演精度,具备进一步探索更大范围激光雷达数据海浪要素提取和分析的潜力。
基金The Key Technologies Research on HY-1B Satellite Data Applications:JT0805the Composite Investigation and Evaluation on China Offshore Ocean:908-03-02-08
文摘This paper proposes the retrieval method of ocean wave spectrum for airborne radar observations at small incidence angles, which is slightly modified from the method developed by Hauser. Firstly, it makes use of integration method to estimate total mean square slope instead of fitting method, which aims to reduce the affects of fluctuations superposed on normalized radar cross-section by integration. Secondly, for eliminating the noise spectrum contained in signal spectrum, the method considers the signal spectrum in certain look direction without any long wave components as the assumed noise spectrum, which would be subtracted from signal spectrum in any look direction for linear wave spectrum retrieval. Estimated v from the integration method are lower than the one from fitting method and have a standard deviation of 0.004 between them approximately. The assumed noise spectrum energy almost has no big variations along with the wave number and is slightly lower to the high wave number part of signal spectrum in any look direction, which follows that the assumption makes sense. The retrieved directional spectra are compared with the buoy records in terms of peak wavelength, peak direction and the significant wave height. Comparisons show that the retrieved peak wavelength and significant wave height are slightly higher than the buoy records but don＇t differs significantly （error less than 10%）. For peak direction, the swell waves in first case basically propagate in the wind direction 6 hours ago and the wind-generated waves in second case also propagate in the wind direction, but the 180° ambiguity remains. Results show that the modified method can carry out the retrieval of directional wave spectrum.
基金National Key Research and Development Program of China(Grants No. 2017YFA0304202 and No. 2017YFA0205700)the NSFC (Grants No. 11 875 231 and No. 11 935 012)the Fundamental Research Funds for the Central Universities through Grant No. 2018FZA3005。
文摘We explore the general characteristics of a matter-wave Sagnac interferometer in a two-parameter estimation scheme. We find that the measurement precisions of both parameters cannot reach the Heisenberg limit(HL) simultaneously when the input state is maximally entangled. Only one of the parameters' uncertainties can approach the HL while the other is scaled by the standard quantum limit.We provide the conditions with which the measurement precision of the specific parameter can reach the HL. We also discuss and figure out the concrete expressions of the constraint conditions for saturating the quantum Cramér–Rao bound. To satisfy these constraint conditions, the evolution time has to be a series of discrete values. Additionally, we calculate the variances of the parameters through some examples under these constraint conditions. The results provided in our work show some intrinsic features of the matter-wave Sagnac interferometer for the two-parameter estimation, which can be valuable in actual experiments.
基金We would like to thank Remote Sensing Ground Station of China, Chinese Academy of Sciences （CAS） and European Space Agency for providing the ERS-1/2 SAR, ENVISAT ASAR and Radarsat-1 SAR images, the CISL Research Data Archive （RDA） for providing the NCEP reanalysis wind data, both http：//www.nodc.noaa.gov/and http：//iridl. ldeo,columbia.edu for providing the Levitus98 data and SODA data, and Dr. R. Romeiser for sharing the radar microwave backscatter imaging model of M4S. This research is jointly supported by the National Natural Science Foundation of China （Grant Nos. 41106155 and 41471227） and under the Open Fund of State Key Laboratory of Satellite Ocean Environment Dynamics （No. SOEDI407）. This work is also supported by General Research Fund of Hong Kong Research Grants Council （RGC） under grants CUHK 402912 and 403113. We also would like to thank the anonymous reviewers＇ comments to improve the original manuscript.
文摘Based on oceanic internal wave SAR imaging mechanism and the microwave scattering imaging model for oceanic surface features, we developed a new method to extract internal wave parameters from SAR imagery. Firstly, the initial wind fields are derived from NCEP reanalysis data, the sea water density and oceanic internal wave pycnocline depth are estimated from the Levites data, the surface currents induced by the internal wave are calculated according to the KDV equation. The NRCS profile is then simulated by solving the action balance equation and using the sea surface radar backscatter model. Both the winds and internal wave pycnocline depth are adjusted by using the dichotomy method step by step to make the simulated data approach the SAR image. Then, the wind speed, pycnocline depth, the phase speed, the group velocity and the amplitude of internal wave can be retrieved from SAR imagery when a best fit between simulated signals and the SAR image appears. The method is tested on one scene SAR image near Dongsha Island, in the South China Sea, results show that the simulated oceanic internal wave NRCS profile is in good agreement with that on the SAR image with the correlation coefficient as high as 90%, and the amplitude of oceanic internal wave retrieved from the SAR imagery is comparable with the SODA data. Besides, the phase speeds retrieved from other 16 scene SAR images in the South China Sea are in good agreement with the empirical formula which describes the relations between internal wave phase speed and water depths, both the root mean square and relative error are less than O. 11 m.s 1 and 7%, respectively, indicating that SAR images are useful for internal wave parameters retrieval and the method developed in this paper is convergent and applicable.
