SAR图像船行尾迹检测的Radon变换和形态学图像处理技术

该文提出了一种由Radon变换与形态学图像处理技术检测船行尾迹的算法SWDRM (ShipWakeDetec tionAlgorithmbasedonRadontransformationandMorphologicimageprocessingtechnology)。算法特点是 :在Radon空间进行处理后 ,得到逆变换图像。通过图像后处理 ,可得到二值图像 ,以用于尾迹自动检测。对海洋卫星合成孔径雷达 (SEASATSAR)图像及模拟乘性斑点噪声中舰船尾迹进行了检测。结果表明 ,SWDRM具有很好的鲁棒性 ,能够适应不同水平的噪声环境。同时 ,对阈值系数和工作窗口宽度的选择范围都比较大 ,在一定的噪声水平范围 ,给定阈值系数后 ,得到近似于恒虚警率的检测结果 ,结合图像后处理 。

干扰及参数扰动条件下的航迹镇定滑模控制

以欠驱动船舶船迹控制应用为背景,提出一种在外界干扰和参数扰动条件下的船舶镇定滑模控制算法。为有效抑制常规滑模控制器的抖振,提高在受到外部环境干扰和参数摄动时的鲁棒性,提出基于BP神经网络的非线性自抗扰滑模控制算法。仿真结果表明,该方法能够有效应对风流干扰,具有很好的鲁棒性。

DETECTION OF SHIP WAKES IN SAR IMAGE USING ROTATED WINDOW RADON TRANSFORM

A novel method of rotated window Radon transform is developed for identifying the linear texture in SAR image.It is applied to automatic detection of the ship wakes of SEASAT SAR image.The location and direction of the traveling ship can be quickly and accurately detectec,In some cases, the ship velocity can also be obtained.

SIMULATION OF SHIP GENERATED TURBULENT AND VORTICAL WAKE IMAGING BY SAR

Synthetic Aperture Radar (SAR) imaging of ocean surface features is studied. The simulation of the turbulent and vortical features generated by a moving ship and SAR imaging of these wakes is carried out. The turbulent wake damping the ocean surface capillary waves may be partially responsible for the suppression of surface waves near the ship track. The vortex pair generating a change in the lateral flow field behind the ship may be partially responsible for an enhancement of the waves near the edges of the smooth area. These hydrodynamic phenomena as well as the changes of radar backscatter generated by turbulence and vortex are simulated.An SAR imaging model is then used on such ocean surface features to provide SAR images.Comparison of two ships' simulated SAR images shows that the wake features are different for various ship parameters.

TR-PIV Analysis of Turbulent Wake of Hydrofoil with Beveled Trailing Edge

The turbulent wakes behind trailing edge are analyzed for understanding of the flow mechanisms responsible for the generation of trailing edge noise. The TILS （turbulence integral length scale） of the turbulent wake of hydrofoil with blunt trailing edge is calculated from TR-PIV （time-resolved particle image velocimetry） data. The temporal auto-correlation method based on Taylor hypothesis and spatial correlation method are used to get the TILS information of the turbulent wake of hydrofoil, respectively The comparison of results by two methods indicates that the spatial correlation method is independent on Taylor hypothesis and suitable to strong turbulence and non-isotropic turbulence.

电子器件

Y99-61821-1316 2001925采用航空磁换能器的船迹探测=Detection of ship wakeusing an airborne magnetic transducer[会,英]/Zou,N.& Nehorai,A.//1998 32nd Asilomar Conference,Vol.2.—1316～1321(PC)N99-06271 2001926电子情报通信学会技术研究报告:超导电子学 SCE98-37～44(信学技报,Vol.98,No.564)[汇。

Stagnant low-energy ions in the near cusp region observed by Cluster

Measuring the low-energy ions in the Earth's magnetotail lobes is difficult, because a spacecraft becomes positively charged in a sunlit and tenuous plasma environment. Recent studies have introduced a new method, making use of the positive electric potential on the Cluster spacecraft, to measure the low-energy ions(less than a few tens of electronvolts) in the polar caps/magnetotail lobes in the years 2001–2010. With the measured velocities, we are able to study the trajectories of these low-energy ions. Particle tracing has been used in previous studies, confirming that ions of ionospheric origin are the dominant contributor to the ion population in the Earth's magnetotail lobes. In this work, we continue to study the source of low-energy ions measured in the lobes. We found that not all of the low-energy ions in the lobes come directly from the ionosphere. Particle tracing infers that some of the low-energy ions start to move tailward from the cusp/near-cusp region with a zero parallel velocity. In the following, we refer to these low-energy ions as stagnant low-energy ions. On the other hand, the in situ measurements by Cluster show a population of low-energy ions in the cusp/near-cusp region with pitch angles near 90°(i.e., no significant parallel velocity).The locations of stagnant low-energy ions are determined by particle tracing and in situ measurements. Similar ion energies and spatial distributions determined by these two methods confirm the presence of the stagnant low-energy ion population.

Solar sailing trajectory optimization with planetary gravity assist

Significant propellant mass saving can be obtained with the use of complex multiple intermediate flyby maneuvers for conventional propulsion systems,and trip time also decreases for a portion of the proper solar sail missions.This paper discusses the performance of gravity assist(GA)in the time-optimal control problem of solar sailing with respect to sail lightness number and the energy difference between the initial and final orbit in the rendezvous problem in a two-body model,in which the GA is modeled as a substantial change in the velocity of the sailcraft at the GA time.In addition,this paper presents a method to solve the time-optimal problem of solar sailing with GA in a full ephemeris model,which introduces the third body’s gravity in a dynamic equation.This study builds a set of inner constraints that can describe the GA process accurately.Finally,this study presents an example for evaluating the accuracy and rationality of the two-body model’s simplification of GA by comparison with the full ephemeris model.

Prediction of the trajectory of the manned spacecraft SHENZHOU-7 deploying a parachute based on a fine wind field

Given that horizontal wind plays an important role in predicting the trajectory of the manned spacecraft SHENZHOU-7 when employing a parachute, the China Meteorological Administration conducted an experiment involving high-resolution wind ob servation, analysis and prediction between September 21 and 28, 2008. In this work, an algorithm for tracking a spacecraft de ploying a parachute is studied. High-resolution wind profiles obtained from a numerical weather model, upper-atmosphere soundings and mobile incoherent Doppler wind lidar are compared. Forward and backward trajectory predictions based on various wind profiles, as well as their differences, are presented. In addition, the trajectory of SHENZHOU-7 is predicted using different wind profiles, and the predicted parachute-opening and landing points are compared with the observed points. Results indicate that a high-resolution numerical weather model and fine observation data can offer more-detailed wind information for the prediction of spacecraft trajectories and can thus help in the editing and sending of flight commands, consequently increas ing the accuracy and reliability of landing on an assigned spot and reducing the search area and rescue time.

Path Following Control of Underactuated Ships Based on Unscented Kalman Filter

A path following controller is proposed to force an underactuated surface ship which is suffering from disturbance to follow a predefined path.The controller is based on analytic model predictive control and unscented Kalman filter(UKF) techniques.The analytic model predictive control provides a systematic method to get appropriate controller parameters to guarantee the stability of the closed-loop system,and the well-defined relative degree is guaranteed by introducing output-redefinition.The UKF is used to estimate the states and uncertain parameters due to time-varying added mass matrices.With help of the proposed UKF-based controller,the underactuated ship with time-varying parameters can follow a desired straight path.Simulation results are presented to demonstrate the effectiveness of the proposed controller.