scholarly journals Range Localization of a Moving Source Based on Synthetic Aperture Beamforming Using a Single Hydrophone in Shallow Water

2020 ◽  
Vol 10 (3) ◽  
pp. 1005
Author(s):  
Jin-Yan Du ◽  
Zong-Wei Liu ◽  
Lian-Gang Lü
Keyword(s):  
Radial Velocity ◽  
Shallow Water ◽  
A Priori ◽  
Simulated Data ◽  
Synthetic Aperture ◽  
Integration Time ◽  
Theoretical Derivation ◽  
Moving Source ◽  
Wavenumber Spectrum ◽  
Priori Information

To localize a moving source in shallow water with a single hydrophone, a passive range localization method based on synthetic aperture beamforming is proposed. First, the horizontal wavenumber spectrum excited by the source is obtained by synthetic aperture beamforming. Then, according to the theoretical derivation (when the integration time is short, the maximum value of the horizontal wavenumber spectrum is related to the average horizontal wavenumber and the radial velocity of the source), the radial velocity can be obtained after obtaining the average horizontal wavenumber. Finally, in the case where there is a closest point of approach (CPA), the range can be recovered from estimation of the range and time of CPA, and from the constant source speed alone the linear track by fitting the source velocity with the model of radial velocity. The only a priori information required is the sound velocity in water. The processing results using simulated data and SWellEx-96 experimental data show that the proposed method can effectively estimate the range of a moving source in shallow sea.

scholarly journals Application of tomographic inversion in studying airglow in the mesopause region

1998 ◽  
Vol 16 (10) ◽  
pp. 1180-1189 ◽  
Author(s):  
T. Nygrén ◽  
M. J. Taylor ◽  
M. S. Lehtinen ◽  
M. Markkanen
Keyword(s):  
Gravity Waves ◽  
Random Noise ◽  
A Priori ◽  
Lower Thermosphere ◽  
Vertical Plane ◽  
Simulated Data ◽  
Altitude Range ◽  
Priori Information ◽  
Two Stages ◽  
Atmospheric Gravity

Abstract. It is pointed out that observations of periodic nightglow structures give excellent information on atmospheric gravity waves in the mesosphere and lower thermosphere. The periods, the horizontal wavelengths and the phase speeds of the waves can be determined from airglow images and, using several cameras, the approximate altitude of the luminous layer can also be determined by triangulation. In this paper the possibility of applying tomographic methods for reconstructing the airglow structures is investigated using numerical simulations. A ground-based chain of cameras is assumed, two-dimensional airglow models in the vertical plane above the chain are constructed, and simulated data are calculated by integrating the models along a great number of rays with different elevation angles for each camera. After addition of random noise, these data are then inverted to obtain reconstructions of the models. A tomographic analysis package originally designed for satellite radiotomography is used in the inversion. The package is based on a formulation of stochastic inversion which allows the input of a priori information to the solver in terms of regularization variances. The reconstruction is carried out in two stages. In the first inversion, constant regularization variances are used within a wide altitude range. The results are used in determining the approximate altitude range of the airglow structures. Then, in the second inversion, constant non-zero regularization variances are used inside this region and zero variances outside it. With this method reliable reconstructions of the models are obtained. The number of cameras as well as their separations are varied in order to find out the limitations of the method.Key words. Tomography · Airglow · Mesopause · Gravity waves

scholarly journals A Synthetic Aperture Radar (SAR)-Based Technique for Microwave Imaging and Material Characterization

Electronics ◽  
2018 ◽  
Vol 7 (12) ◽  
pp. 373 ◽  
Author(s):  
Yuri Álvarez López ◽  
María García Fernández ◽  
Raphael Grau ◽  
Fernando Las-Heras
Keyword(s):  
Synthetic Aperture Radar ◽  
Material Characterization ◽  
A Priori ◽  
Microwave Imaging ◽  
Synthetic Aperture ◽  
Sar Image ◽  
A Priori Information ◽  
Priori Information ◽  
Constitutive Parameters ◽  
Aperture Radar

This contribution presents a simple and fast Synthetic Aperture Radar (SAR)-based technique for microwave imaging and material characterization from microwave measurements acquired in tomographic systems. SAR backpropagation is one of the simplest and fastest techniques for microwave imaging. However, in the case of heterogeneous objects and media, a priori information about the constitutive parameters (conductivity, permittivity) is needed for an accurate imaging. In some cases, a first guess of the constitutive parameters can be extracted from an uncorrected SAR image, and then the estimated parameters can be introduced in a second step to correct the SAR image. The main advantage of this methodology is that there is little or no need for a priori information about the object to be imaged. Besides, calculation time is not significantly increased with respect to conventional SAR, thus allowing real-time imaging capabilities. The methodology has been validated by means of measurements acquired in a cylindrical setup.

scholarly journals An improved method using adaptive smoothing for GNSS tomographic imaging of ionosphere

PLoS ONE ◽  
2021 ◽  
Vol 16 (5) ◽  
pp. e0250613
Author(s):  
Rushang Jia ◽  
Xumin Yu ◽  
Jianping Xing ◽  
Yafei Ning ◽  
Hecheng Sun
Keyword(s):  
A Priori ◽  
Simulated Data ◽  
Reconstruction Technique ◽  
Electron Content ◽  
Observation Data ◽  
A Priori Information ◽  
Improved Method ◽  
Adaptive Smoothing ◽  
Total Electron ◽  
Priori Information

Global navigation satellite system (GNSS) is a well-established sensors in the recent ionosphere research. By comparing with classical meteorological equipments, the GNSS application can obtain more reliable and precious ionospheric total electron content (TEC) result. However, the most used GNSS ionospheric tomography technique is sensitive to a priori information due to the sparse and non-uniform distribution of GNSS stations. In this paper, we propose an improved method based on adaptive Laplacian smoothing and algebraic reconstruction technique (ALS-ART). Compared with traditional constant constraints, this method is less dependent on a priori information and adaptive smoothing constraints is closer to the actual situation. Tomography experiments using simulated data show that reconstruction accuracy of ionospheric electron density using ALS-ART method is significantly improved. We also use the method to do the analysis of real observation data and compare the tomography results with ionosonde observation data. The results demonstrate the superiority and reliability of the proposed method compared to traditional constant constraints method which will further improve the capability of obtaining precious ionosphere TEC by using GNSS.

scholarly journals Moving Source Depth Estimation Using a Horizontal Line Array in Shallow Water Waveguides

2018 ◽  
Author(s):  
Liang Guolong ◽  
Zhang Yifeng ◽  
Zou Nan ◽  
Wang Jinjin
Keyword(s):  
Shallow Water ◽  
Estimation Method ◽  
Depth Estimation ◽  
Propagation Model ◽  
Small Range ◽  
Horizontal Line ◽  
Source Depth ◽  
Moving Source ◽  
Line Array ◽  
Wavenumber Spectrum

In this study, a matched-mode autoregressive source depth estimation method (MMAR) based on autoregressive (AR) wavenumber estimation is proposed for a moving source in shallow water waveguides. The signal original frequency and the environmental parameters, namely, the sound speed profile and bottom properties are known as a prior knowledge. The mode wavenumbers are estimated by the AR modal wavenumber spectrum. On the basis of the mode wavenumber estimation, the mode amplitudes can be estimated by the wavenumber spectrum that is obtained by generalized Hankel transform. The source depth estimation is determined by the peak of source depth function wherein the data mode best matches the replica mode that is calculated using a propagation model. Compared with other methods of moving source depth estimation, the proposed method exhibits a better performance in source depth estimation under low signal-to-noise ratio or the small range span. The selection of horizontal line array depth is illustrated by simulation and normal mode theory in details.

scholarly journals Reconstruction of the cosmic equation of state for high redshift

2019 ◽  
Vol 79 (12) ◽  
Author(s):  
A. M. Velasquez-Toribio ◽  
M. M. Machado ◽  
Julio C. Fabris
Keyword(s):  
Equation Of State ◽  
Gamma Ray ◽  
High Redshift ◽  
A Priori ◽  
Parametric Method ◽  
Simulated Data ◽  
Quality Data ◽  
Model Independent ◽  
Priori Information ◽  
Non Parametric

AbstractWe investigate the possibilities of reconstructing the cosmic equation of state (EoS) for high redshift. In order to obtain general results, we use two model-independent approaches. The first reconstructs the EoS using comoving distance and the second makes use of the Hubble parameter data. To implement the first method, we use a recent set of Gamma-Ray Bursts (GRBs) measures. To implement the second method, we generate simulated data using the Sandage–Loeb (SL) effect; for the fiducial model, we use the $$\Lambda CDM$$ΛCDM model. In both cases, the statistical analysis is conducted through the Gaussian processes (non-parametric). In general, we demonstrate that this methodology for reconstructing the EoS using a non-parametric method plus a model-independent approach works appropriately due to the feasibility of calculation and the ease of introducing a priori information ($$H_ {0}$$H0 and $$\Omega _{m0}$$Ωm0). In the near future, following this methodology with a higher number of high quality data will help obtain strong restrictions for the EoS.

scholarly journals Match-Mode Autoregressive Method for Moving Source Depth Estimation in Shallow Water Waveguides

2018 ◽  
Vol 2018 ◽  
pp. 1-15 ◽  
Author(s):  
Liang Guo-Long ◽  
Zhang Yi-Feng ◽  
Zou Nan ◽  
Wang Jin-Jin
Keyword(s):  
Shallow Water ◽  
Depth Estimation ◽  
Propagation Model ◽  
Estimation Methods ◽  
Small Range ◽  
Horizontal Line ◽  
Source Depth ◽  
Moving Source ◽  
Line Array ◽  
Wavenumber Spectrum

Source depth estimation is always a problem in underwater acoustic area, because depth estimation is a nonlinear problem. Traditional depth estimation methods use a vertical line array, which has disadvantage of poor mobility due to the size of sensor array. In order to estimate source depth with a horizontal line array, we propose a matched-mode depth estimation method based on autoregressive (AR) wavenumber estimation for a moving source in shallow water waveguides. First, we estimate the mode wavenumbers using the improved AR modal wavenumber spectrum. Second, according to the mode wavenumber estimation, we estimate the mode amplitudes by the wavenumber spectrum, which is obtained by generalized Hankel transform. Finally, we estimate source depth estimation by the peak of source depth function wherein the data mode best matches the replica mode that is calculated using a propagation model. Compared with synthetic aperture beamforming, the proposed method exhibits a better performance in source depth estimation under low signal-to-noise ratio or the small range span. The robustness of the proposed method is illustrated by simulating the performance in mismatched environment.

Innovative Approach to Information Search by Example of a Patent Analysis of an Important Substitution Plan

2020 ◽  
pp. 143-157
Author(s):  
Maria A. Milkova
Keyword(s):  
Information Search ◽  
Topic Modeling ◽  
Cognitive Biases ◽  
A Priori ◽  
Import Substitution ◽  
Innovative Approach ◽  
Iterative Search ◽  
Comprehensive Picture ◽  
Priori Information ◽  
Selection Of

Nowadays the process of information accumulation is so rapid that the concept of the usual iterative search requires revision. Being in the world of oversaturated information in order to comprehensively cover and analyze the problem under study, it is necessary to make high demands on the search methods. An innovative approach to search should flexibly take into account the large amount of already accumulated knowledge and a priori requirements for results. The results, in turn, should immediately provide a roadmap of the direction being studied with the possibility of as much detail as possible. The approach to search based on topic modeling, the so-called topic search, allows you to take into account all these requirements and thereby streamline the nature of working with information, increase the efficiency of knowledge production, avoid cognitive biases in the perception of information, which is important both on micro and macro level. In order to demonstrate an example of applying topic search, the article considers the task of analyzing an import substitution program based on patent data. The program includes plans for 22 industries and contains more than 1,500 products and technologies for the proposed import substitution. The use of patent search based on topic modeling allows to search immediately by the blocks of a priori information – terms of industrial plans for import substitution and at the output get a selection of relevant documents for each of the industries. This approach allows not only to provide a comprehensive picture of the effectiveness of the program as a whole, but also to visually obtain more detailed information about which groups of products and technologies have been patented.

Sign in / Sign up

Export Citation Format

Share Document