海底单参数频域反演与沉积物分类

为了快速获取海底声学特性,从降低反演参数维数入手,提出一种基于海底单参数(小掠射角下海底反射损失随掠射角的变化率)的频域反演方法,并用于沉积物分类。在海底单参数模型基础上,对海底反射信号进行频域相关处理,利用几何射线理论,推导获得海底单参数与归一化频域自相关系数下降至0.5时频移量之间的关系表达式。通过研究海底单参数与沉积物类型之间的等效关系,对海底沉积物进行分类。对波兰波罗的海实验数据进行实际反演,得到1000~2500 Hz频段内的海底单参数值,进而判定实验海域海底沉积物类型为极细砂。结果表明,根据单参数反演值预报的声传播损失与实验测量值符合较好,利用频域反演结果获得的海底沉积物类型与取样结果一致,验证了实验海域频域反演方法的有效性及分类结果的正确性。      

利用传播损失反演海底单参数

根据地声反演复杂性随着待反演参数的个数减少不断降低的原理,提出一种利用传播损失反演海底单个参数的方法。通过对海底声阻抗的推导,利用声速、密度和衰减系数拟合出海底反射损失对掠射角的斜率F。基于简正波理论推导了用F描述声场的公式,并据此设计出对传播损失数据进行最小二乘法处理的反演方法。得益于将待反演参数减少至一个,该方法只需单个水听器,避免了复杂测量及多维寻优。对东海实验数据进行了实际反演,并介绍了利用反演结果F进行传播损失预报和海底性质估计的步骤。所获结果与多参数混合反演方法及实测真值进行比较,其一致性验证了方法的有效性。      

基于大掠射角海底反射特性的深海地声参数反演

海底声学参数的获取对于海洋声学研究有着重要意义.通过推导分层吸收介质下的海底反射系数,理论分析了大掠射角条件下吸收系数对海底反射系数的影响.海底反射系数随频率振荡过程中,将其等于海水-沉积层界面反射系数模时所对应的频点定义为1/4振荡周期频率.在该频率下,沉积层吸收系数与基底地声参数的耦合程度小于其他频点.本文基于大掠射角下的海底反射特性,提出一种深海地声参数分步反演方法.首先,利用相关法提取得到海底反射系数的干涉周期,利用干涉周期反演了沉积层声速和厚度.声速的反演结果结合Hamilton经验公式反演密度.第二步,通过结合基底声速的穷举边界,给出沉积层吸收系数的假设值,利用1/4振荡周期频率下的海底反射系数对基底声速进行一维反演.最后利用半波层频率下的海底反射系数对沉积层吸收系数进行一维反演.大掠射角海底反射特性结合分步反演,实现了基底声速和沉积层吸收系数一定程度的解耦合.实验结果表明,在大掠射角测量条件下,该方法反演的地声参数可有效应用在一定范围内的传播损失预报.     

基于拖曳倾斜线列阵的海底反射损失提取方法

在浅海环境中,海底声学参数对水下声场的精确预报十分重要.现有的海底声学参数反演方法大多数是采用固定垂直阵进行的,其缺点是不能实施大面积、高分辨的走航式反演.在已提出的垂直阵海底反射损失反演方法的基础上,研究了基于三种线列阵阵形的海底反射损失提取方法及其特点,提出了基于拖曳倾斜线列阵与三个声源组合的走航式海底参数快速获取方法,并对该方法进行了误差分析.研究结果表明：覆盖同样的掠射角范围,垂直线列阵需与多个距离的声源组合,拖曳水平线列阵只需一个声源组合但需要采用较大的物理孔径,拖曳倾斜线列阵综合了垂直阵和水平 关键词： 水下声场预报 海底声学参数 海底反射损失 拖曳倾斜线列阵     

一种海洋环境噪声分步反演地声参数方法

分析不同海底参数对环境噪声垂向空间特性的敏感度,根据海底密度对环境噪声垂直指向性的小掠射角部分不敏感,而对等效海底损失的大掠射角部分相对敏感的特点,提出了一种海洋环境噪声分步反演地声参数方法:先用环境噪声垂直指向性小掠射角部分反演海底声速、衰减;之后利用大掠射角部分来反演海底密度。仿真算例和海上实验数据处理结果验证了该方法的有效性。结果表明:分步反演加强了匹配物理量对海底参数敏感部分的关注,在反演结果精度(海底密度)以及反演效率上都有所改善,具有一定可行性。      

海底反射损失的高分辨率估计方法

在海洋声学中,海底反射损失是一个重要的物理量,不仅可以用于传播损失的计算,也可以用来反演海底参数(如声速、密度、吸收系数等)。海底反射损失与声波频率和掠射角有关,近年来出现了多种估计方法,其中一种简单的被动方法是对环境噪声做垂直波束形成,来自海底与来自海面的噪声比例能够反映出海底反射损失的大小[1]。该方法的一个主要优点是能够直接得到反射损失,不需要任何反演机制。但有一个明显的缺点,当垂直接收     

基于简化海底模型的浅海环境噪声垂直指向性及参数反演

提出了一种以简化海底模型为基础的浅海环境噪声垂直指向性的计算方法,并用于海底参数反演。小掠射角时,采用简正波法;大掠射角时,采用虚源法。数值仿真结果与经典的K/I噪声模型相近;分析某浅水区的一次噪声试验数据,提出分段反演方法,并将反演得到的参数较好的用于噪声场强度预报。结果表明,该方法引入的简化海底模型,能反映出海底反射对噪声场垂直指向性的影响,但由于不需要精确的海底分层结构,便于理论分析声场。      

一种低声速沉积层海底参数声学反演方法

软泥底环境下沉积层参数的声学反演是国际水声领域的一个研究热点.浅海中,当高声速基底和海水之间存在一层低声速(小于海水声速)的沉积层时,小掠射角情况下不同频率声传播损失会出现周期性增大现象.基于此现象,提出一种适用于低声速沉积层的海底参数声学反演方法.首先,推导给出小掠射角情况下传播损失周期增大的频率间隔与沉积层声速、厚度及近海底海水声速之间的解析表达式;其次,利用一次黄海实验中软泥底环境下的宽带声传播信号,提取了小掠射角下传播损失增大的频率周期;再次,把该解析表达式作为约束条件,结合Hamilton密度与声速的经验公式,采用匹配场处理反演给出沉积层的声速、密度、厚度及基底的声速、密度;然后,利用声传播损失数据反演得到泥底环境下不同频率的声衰减系数,通过拟合发现泥底声衰减系数随频率近似呈线性关系;最后,给出了双层海底模型和半无限大海底模型等效性的讨论.反演结果为低声速沉积层海底声传播规律研究与应用提供了海底声学参数.     

基于等效密度流体近似反射模型反演海底参数

为了获取海底沉积物的物理和地声特性,根据等效密度流体近似反射模型得到的不同掠射角下的海底反射损失,利用差分进化算法和粒子群算法相结合的两级混合优化算法以及Bayesian反演方法对海底沉积物的孔隙度、平均颗粒粒度、颗粒质量密度以及颗粒体积弹性模量进行反演,再根据这4个物理参数的估计值进一步计算出海底地声参数,包括声速和衰减。通过反演结果与仿真真值的比较可以看出,除颗粒体积弹性模量外,得到的估计结果是令人满意的,特别是这种间接反演海底地声参数的方法对地声参数的估计具有较高的精确性和较强的稳健性,相对误差分别为0.092%和17%。最后,对实验室水池池底沙质沉积物的反射损失数据进行处理,给出了沙质沉积物各参数的估计值、不确定性和相关性,并通过反演结果与部分实测参数值的比较验证了反演方法的可行性。      

考虑噪声源深度分布的海洋环境噪声模型及地声参数反演

考虑到海洋环境噪声源深度分布不集中,建立了噪声源随深度分布的海洋环境噪声模型,分析了源深度对噪声场垂向特征的影响并从简正波角度予以解释,发现海底声阻抗和声源深度都显著影响由海洋环境噪声获得的等效海底反射损失大掠射角部分,进而将该模型用于地声参数反演.两段实测噪声数据200—525 Hz频段的反演结果表明:基于海洋环境噪声的地声参数反演最优值与声传播的反演结果相近;源平均深度最优值随频率增加有变小的趋势,说明随频率增加环境噪声主要贡献源逐渐由航船转为风浪;当海况大于3级时,400 Hz以上频段噪声源深度平均值很小,与Monahan气泡理论的描述一致.     

一种基于简正波模态频散的远距离宽带海底参数反演方法

在浅海环境中, 海底环境参数对声传播有着重要的影响. 由于利用单个宽带声源进行海底参数反演时, 随着距离的增大, 误差变大, 本文提出利用warping变换对在浅海波导中传播的, 不同距离上的两个宽带爆炸声源进行简正波的有效分离, 实现了宽带爆炸声源的远距离海底参数反演. 采用全局寻优遗传算法对提取出的模态频散到达时间差与理论计算的模态频散到达时间差进行匹配处理, 并结合随距离连续变化的声传播损失, 实现了利用单水听器进行海底参数的反演. 实验结果表明: 运用反演出的海底参数提取模态频散时间差和实测数据提取出的模态频散时间差吻合得较好; 而通过传播损失反演得到的海底衰减系数与频率呈指数关系. 最后, 对反演结果进行了后验概率分析, 并将本组爆炸声源的反演结果用于另一组不同距离上爆炸声源时仍然有效, 来评价反演结果的有效性.     

Geoacoustic Inversion for Bottom Parameters via Bayesian Theory in Deep Ocean

We develop a new approach to estimating bottom parameters based on the Bayesian theory in deep ocean.The solution in a Bayesian inversion is characterized by its posterior probability density(PPD),which combines prior information about the model with information from an observed data set.Bottom parameters are sensitive to the transmission loss(TL)data in shadow zones of deep ocean.In this study,TLs of different frequencies from the South China Sea in the summer of 2014 are used as the observed data sets.The interpretation of the multidimensional PPD requires the calculation of its moments,such as the mean,covariance,and marginal distributions,which provide parameter estimates and uncertainties.Considering that the sensitivities of shallowzone TLs vary for different frequencies of the bottom parameters in the deep ocean,this research obtains bottom parameters at varying frequencies.Then,the inversion results are compared with the sampling data and the correlations between bottom parameters are determined.Furthermore,we show the inversion results for multifrequency combined inversion.The inversion results are verified by the experimental TLs and the numerical results,which are calculated using the inverted bottom parameters for different source depths and receiver depths at the corresponding frequency.     

Optical simulation of CsPbI3/TOPCon tandem solar cells with advanced light management

Monolithic perovskite/Si tandem solar cells (TSCs) have experienced rapid development in recent years, demonstrating its potential to exceed the Shockley-Queisser limit of single junction Si solar cells. Unlike typical organic-inorganic hybrid perovskite/silicon heterojunction TSCs, here we propose CsPbI₃/TOPCon TSC, which is a promising architecture in consideration of its pleasurable thermal stability and good compatibility with current PERC production lines. The optical performance of CsPbI₃/TOPCon TSCs is simulated by the combination of ray-tracing method and transfer matrix method. The light management of the CsPbI₃/TOPCon TSC begins with the optimization of the surface texture on Si subcell, indicating that a bifacial inverted pyramid with a small bottom angle of rear-side enables a further minimization of the optical losses. Current matching between the subcells, as well as the parasitic absorption loss from the front transparent conductive oxide, is analyzed and discussed in detail. Finally, an optimized configuration of CsPbI₃/TOPCon TSC with a 31.78% power conversion efficiency is proposed. This work provides a practical guidance for approaching high-efficiency perovskite/Si TSCs.     

利用气枪声源数据的地声参数反演*

本文通过对东海采集的气枪声源数据进行处理,基于地声参数对不同声场观测量的敏感性差异,利用分步反演的策略进行分析。首先选择距离接收阵七个不同的距离点数据,通过warping变换准确提取第三阶至第八阶简正波的频散曲线;利用海底声速对频散曲线敏感的特性来反演声速;由Hamilton经验公式求得海底密度;通过传播损失拟合获得海底衰减。不同距离点数据反演的海底声速与密度一致性较高。实验提取的频散曲线和和反演参数仿真结果、实验获取的传播损失与反演参数获得传播损失均拟合较好。     

Geoacoustic Inversion Based on a Vector Hydrophone Array

We propose a geoacoustic inversion scheme employing a vector hydrophone array based on the fact that vector hydrophone can provide more acoustic field information than traditional pressure hydrophones. Firstly, the transmission loss of particle velocities is discussed. Secondly, the sediment sound speed is acquired by a matchedfield processing （MFP） procedure, which is the optimization in combination of the pressure field and vertical particle velocity field. Finally, the bottom attenuation is estimated from the transmission loss difference between the vertical particle velocity and the pressure. The inversion method based on the vector hydrophone array mainly has two advantages： One is that the MFP method based on vector field can decrease the uncertain estimation of the sediment sound speed. The other is that the objective function based on the transmission loss difference has good sensitivity to the sediment attenuation and the inverted sediment attenuation is independent of source level. The validity of the inverted parameters is examined by comparison of the numerical results with the experimental data.     

Minimal renormalization without ε-expansion: Three-loop amplitude functions of the 0(n) symmetric Φ theory in three dimensions below Tc

We present an analytic three-loop calculation for thermodynamic quantities of the O(n) symmetric Φ⁴ theory below T_c within the minimal subtraction scheme at fixed dimension d = 3. Goldstone singularities arising at an intermediate stage in the calculation of O(n) symmetric quantities cancel among themselves leaving a finite result in the limit of zero external field. From the free energy we calculate the three-loop terms of the amplitude functions ƒ_Φ, F₊ and F₋ of the order parameter and the specific heat above and below Tc, respectively, without using the e = 4-d expansion. A Borel resummation for the case n = 2 yields resummed amplitude functions f_Φ and F₋ that are slightly larger than the one-loop results. Accurate knowledge of these functions is needed for testing the renormalization-group prediction of critical-point universality along the λ₋line of superfluid ⁴He. Combining the three-loop result for F₋ with a recent five-loop calculation of the additive renormalization constant of the specific heat yields excellent agreement between the calculated and measured universal amplitude ratio A⁺/A^- of the specific heat of ⁴He. In addition we use our result for f_Φ to calculate the universal combination Rc of the amplitudes of the order parameter, the susceptibility and the specific heat for n = 2 and n = 3. Our Borel-resummed three-loop result for R_c is significantly more accurate than the previous result obtained from the ε-expansion up to O(ε².     

Geoacoustic inversion with ships as sources

Estimation of geoacoustic parameters using acoustic data from a surface ship was performed for a shallow water region in the Gulf of Mexico. The data were recorded from hydrophones in a bottom mounted, horizontal line array (HLA). The techniques developed to produce the geoacoustic inversion are described, and an efficient method for geoacoustic inversion with broadband beam cross-spectral data is demonstrated. The performance of cost functions that involve coherent or incoherent sums over frequency and one or multiple time segments is discussed. Successful inversions for the first sediment layer sound speed and thickness and some of the parameters for the deeper layers were obtained with the surface ship at nominal ranges of 20, 30, or 50 water depths. The data for these inversions were beam cross-spectra from four subapertures of the HLA spanning a little more than two water depths. The subaperture beams included ten frequencies equally spaced in the 120-200 Hz band. The values of the geoacoustic parameters from the inversions are validated by comparisons with geophysical observations and with the parameter values from previous inversions by other invesigators, and by comparing transmission loss (TL) measured in the experiment with modeled TL based on the inverted geoacoustic parameters.