Time filter

Source Type

Liu Y.,CAS Beijing Institute of Geographic Sciences and Nature Resources Research | Xi D.-G.,Zhengzhou University | Xi D.-G.,Naval Institute of Hydrographic Surveying and Charting | Li Z.-L.,Chinese Academy of Agricultural Sciences | And 2 more authors.
Atmosphere | Year: 2014

Although cumulonimbus (Cb) clouds are the main source of precipitation in south China, the relationship between Cb cloud characteristics and precipitation remains unclear. Accordingly, the primary objective of this study was to thoroughly analyze the relationship between Cb cloud features and precipitation both at the pixel and cloud patch scale, and then to apply it in precipitation estimation in the Huaihe River Basin using China's first operational geostationary meteorological satellite, FengYun-2C (FY-2C), and the hourly precipitation data of 286 gauges from 2007. First, 31 Cb parameters (14 parameters of three pixel features and 17 parameters of four cloud patch features) were extracted based on a Cb tracking method using an artificial neural network (ANN) cloud classification as a pre-processing procedure to identify homogeneous Cb patches. Then, the relationship between Cb cloud properties and precipitation was analyzed and applied in a look-up table algorithm to estimate precipitation. The results were as follows: (1) Precipitation increases first and then declines with increasing values for cold cloud and time evolution parameters, and heavy precipitation may occur not only near the convective center, but also on the front of the Cb clouds on the pixel scale. (2) As for the cloud patch scale, precipitation is typically associated with cold cloud and rough cloud surfaces, whereas the coldest and roughest cloud surfaces do not correspond to the strongest rain. Moreover, rainfall has no obvious relationship with the cloud motion features and varies significantly over different life stages. The involvement of mergers and splits of minor Cb patches is crucial for precipitation processes. (3) The correlation coefficients of the estimated rain rate and gauge rain can reach 0.62 in the cross-validation period and 0.51 in the testing period, which indicates the feasibility of the further application of the relationship in precipitation estimation. © 2014 by the authors.

Wu Y.,CAS Beijing Institute of Acoustics | Yan S.,CAS Beijing Institute of Acoustics | Li S.,Naval Institute of Hydrographic Surveying and Charting | Song H.,University of Chinese Academy of Sciences
OCEANS 2016 - Shanghai | Year: 2016

Underwater navigation that relies solely on dead reckoning suffers from unbounded position error growth. In traditional positioning method, the cost and trouble of deploying, recovering, and assembly have become insuperable obstacle. Based on combination SLBL with an Argo float, a new positioning method of autonomous navigation is proposed in the paper. In order to improve the ranging accuracy, with the pattern time delay shift coding system, the second correlation method is given for time delay estimation in this paper. The superiority of the second cross-correlation method is that time delay could be estimated in a lower signal-to-noise ratio environment and in the complex multipath channels compared to the first cross-correlation method. At last, some field trial results show that the second correlation method could suppress the multipath interference in underwater channel efficiently, and that the position of moving vehicle is solved from point-to-point based on the estimation of bearing and ranging. © 2016 IEEE.

Sun X.,CAS Institute of Remote Sensing | Yang L.,CAS Institute of Remote Sensing | Zhang B.,CAS Institute of Remote Sensing | Gao L.,CAS Institute of Remote Sensing | Zhang L.,Naval Institute of Hydrographic Surveying and Charting
2013 6th International Conference on Advanced Computational Intelligence, ICACI 2013 - Proceedings | Year: 2013

Pixel clustering is a common hyperspectral image processing technique. Its process is to find the appropriate cluster centers and assign each pixel to a center according to a certain metric. Artificial Bee Colony (ABC) algorithm based pattern clustering is proved to have better performance than traditional clustering methods such as K-means. Therefore, studies on hyperspectral image clustering method based on ABC algorithm are done. The target function and feasible solution space are determined, and the complete process is given. The proposed algorithm and other algorithms are compared and analyzed with the use of two sets of real hyperspectral remote sensing data and ground survey results. © 2013 IEEE.

Zheng S.,CAS South China Sea Institute of Oceanology | Du Y.,CAS South China Sea Institute of Oceanology | Li J.,Naval Institute of Hydrographic Surveying and Charting | Cheng X.,CAS South China Sea Institute of Oceanology
Ocean Science | Year: 2015

Using a geometric eddy identification method, cyclonic and anticyclonic eddies from submesoscale to mesoscale in the South Indian Ocean (SIO) have been statistically investigated based on 2082 surface drifters from 1979 to 2013. A total of 19 252 eddies are identified, 60% of them anticyclonic eddies. For the submesoscale eddies (radius r<10 km), the ratio of cyclonic eddies (3183) to anticyclonic eddies (7182) is 1 to 2. In contrast, the number of anticyclonic and cyclonic eddies with radius rge;10 km is almost equal. Mesoscale and submesoscale eddies show different spatial distributions. Eddies with radius rge;100 km mainly appear in the Leeuwin Current, a band along 25\S, Mozambique Channel, and Agulhas Current, areas characterized by large eddy kinetic energy. The submesoscale anticyclonic eddies are densely distributed in the subtropical basin in the central SIO. The number of mesoscale eddies shows statistically significant seasonal variability, reaching a maximum in October and minimum in February. © Author(s) 2015.

Liang Z.,Naval Institute of Hydrographic Surveying and Charting | Lianru G.,CAS Institute of Remote Sensing | Bing Z.,CAS Institute of Remote Sensing
IOP Conference Series: Earth and Environmental Science | Year: 2014

The seashore, especially coral bank, is sensitive to human activities and environmental changes. A multispectral image, with coarse spectral resolution, is inadaptable for identify subtle spectral distinctions between various beaches. To the contrary, hyperspectral image with narrow and consecutive channels increases our capability to retrieve minor spectral features which is suit for identification and classification of surface materials on the shore. Herein, this paper used airborne hyperspectral data, in addition to ground spectral data to study the beaches in Qingdao. The image data first went through image pretreatment to deal with the disturbance of noise, radiation inconsistence and distortion. In succession, the reflection spectrum, the derivative spectrum and the spectral absorption features of the beach surface were inspected in search of diagnostic features. Hence, spectra indices specific for the unique environment of seashore were developed. According to expert decisions based on image spectrums, the beaches are ultimately classified into sand beach, rock beach, vegetation beach, mud beach, bare land and water. In situ surveying reflection spectrum from GER1500 field spectrometer validated the classification production. In conclusion, the classification approach under expert decision based on feature spectrum is proved to be feasible for beaches.

Fan L.,Naval Institute of Hydrographic Surveying and Charting | Zhai G.,Naval Institute of Hydrographic Surveying and Charting | Chai H.,Zhengzhou University
Cehui Xuebao/Acta Geodaetica et Cartographica Sinica | Year: 2014

Since the round-off error affects the effect and the success rate of the down correlation along with the increase of the matrix's dimension, the idea of block Gram-Schmidt orthogonalization is introduced, and the integer block Gram-Schmidt orthogonalization algorithm is designed, meanwhile, the IBGS-LLL decorrelation algorithm is proposed combined with the LLL algorithm. The decorrelation effect of different block style is analyzed with different dimension by using the random simulation method. It is confirmed the block manner of different measuring mode. Comparison of the IBGS-LLL algorithm with the improved LLL algorithm based on simulated and measured data shows that the IBGS-LLL decorrelation algorithm possessing has better effect and higher success rate of ambiguity decorrelation.

Chen C.-L.,Zhengzhou University | Wei H.-P.,Zhengzhou University | Zhai J.-S.,Naval Institute of Hydrographic Surveying and Charting
ICIME 2010 - 2010 2nd IEEE International Conference on Information Management and Engineering | Year: 2010

In order to achieve a regular-grid based, prospect - dependent 3D visualization system, this paper adopts Pyramid Model, and organizes the terrain data using Linear Quadtree. A method to compute the visible area and the best resolution for terrain is introduced in this paper, as well as an algorithm for predicting the data blocks. A new algorithm called as "Dynamic search algorithm for target blocks taking FPS into account", is brought forward in this paper. A 3D visualization system for large-scale terrain is realized by DirectX9.0 and Visual C#.NET, which achieved a good visual effect and a high and steady FPS just on PC platforms. The experimental result indicates that, the methods or algorithms presented in this paper can not only realize real-time rendering of large-scale terrain, but also can balance between the runtime efficiency and the display precision. © 2010 IEEE.

Wang H.,Zhengzhou University | Chai H.,Zhengzhou University | Chai H.,Naval Institute of Hydrographic Surveying and Charting | Wang M.,Zhengzhou University
Acta Geodaetica et Cartographica Sinica | Year: 2011

Ln view of the fact that the Ordinary Kriging algorithm will be influenced by outliers while processing multibeam bathymetry data, The calculating formula of sample variogram is deduced based on robust estimation, and the influence of outliers in fitting variogram function is controlled. The superiority of the algorithm in exactitude estimating and detecting outliers is proved by real data experiments. The regular square grids of multibeam data are also constructed by the algorithm. The grids values are compared with those which are calculated by manual processing, and they are consistent. It is proved that the seabed terrain grids can be constructed by the proposed algorithm in high precision and outliers can be detected automatically.

Zhai G.,Naval Institute of Hydrographic Surveying and Charting | Bian G.,Naval Institute of Hydrographic Surveying and Charting | Bian G.,Dalian Naval Academy | Huang M.,Naval Institute of Hydrographic Surveying and Charting
Cehui Xuebao/Acta Geodaetica et Cartographica Sinica | Year: 2011

The vertical derivative of the total field magnetic anomaly (TMA) plays an important role in the interpretation process of magnetic objects. Owing to the filter characteristics of vertical derivative operator in frequency domain, the conversion of vertical derivative is inherently unstable and any high-frequency noise presented in the surveying data gets strongly magnified in the transformed map in such a way to mask any useful signal. Based on the harmonic properties of the vertical integral and derivatives of TMA, an algorithm is presented to perform calculation of vertical derivatives using both frequency and space domain transformations. The effectiveness of the suggested techniques has been illustrated by synthetic sphere magnetic model whose TMA's first and second vertical derivative expressions are deduced when the geomagnetic direction is different from magnetization direction. The conclusion indicates that the presented vertical derivatives calculation method provides better results and allows a lower degrading of the signal-to-noise ratio than the standard Fourier method.

Liu M.,Binzhou University | Chang G.,Naval Institute of Hydrographic Surveying and Charting
Mathematical Problems in Engineering | Year: 2015

This paper is concerned with the topic of gravity matching aided inertial navigation technology using Kalman filter. The dynamic state space model for Kalman filter is constructed as follows: the error equation of the inertial navigation system is employed as the process equation while the local gravity model based on 9-point surface interpolation is employed as the observation equation. The unscented Kalman filter is employed to address the nonlinearity of the observation equation. The filter is refined in two ways as follows. The marginalization technique is employed to explore the conditionally linear substructure to reduce the computational load; specifically, the number of the needed sigma points is reduced from 15 to 5 after this technique is used. A robust technique based on Chi-square test is employed to make the filter insensitive to the uncertainties in the above constructed observation model. Numerical simulation is carried out, and the efficacy of the proposed method is validated by the simulation results. © 2015 Ming Liu and Guobin Chang.

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