Speed ambiguity in hurricane wind retrieval from SAR imagery

Under strong ocean surface wind conditions, the normalized radar cross section of synthetic aperture radar (SAR) is dampened at certain incident angles, compared with the signals under moderate winds. This causes a wind speed ambiguity problem in wind speed retrievals from SAR, because two solutions may exist for each backscattered signal. This study shows that the problem is ubiquitous in the images acquired by operational space-borne SAR sensors. Moreover, the problem is more severe for the near range and range travelling winds. To remove this ambiguity, a method was developed based on characteristics of the hurricane wind structure. A SAR image of Hurricane Rita (2005) was analysed to demonstrate the wind speed ambiguity problem and the method to improve the wind speed retrievals. Our conclusions suggest that a speed ambiguity removal algorithm must be used for wind retrievals from SAR in intense storms and hurricanes.

A new wind vector algorithm for C-band SAR

Ocean wind speed and wind direction are estimated simultaneously using the normalized radar cross sections or' corresponding to two neighboring (25-km) blocks, within a given synthetic aperture radar (SAR) image, having slightly different incidence angles. This method is motivated by the methodology used for scatterometer data. The wind direction ambiguity is removed by using the direction closest to that given by a buoy or some other source of information. We demonstrate this method with 11 EN-VISAT Advanced SAR sensor images of the Gulf of Mexico and coastal waters of the North Atlantic. Estimated wind vectors are compared with wind measurements from buoys and scatterometer data. We show that this method can surpass other methods in some cases, even those with insufficient visible wind-induced streaks in the SAR images, to extract wind vectors.

Depth inversion in coastal water based on SAR image of waves

Wave-number spectrum technique is proposed to retrieve coastal water depths by means of Synthetic Aperture Radar (SAR) image of waves. Based on the general dispersion relation of ocean waves, the wavelength changes of a surface wave over varying water depths can be derived from SAR. Approaching the analysis of SAR images of waves and using the general dispersion relation of ocean waves, this indirect technique of remote sensing bathymetry has been applied to a coastal region of Xiapu in Fujian Province, China. Results show that this technique is suitable for the coastal waters especially for the near-shore regions with variable water depths.

Underwater topography detection of Shuangzi Reefs with SAR images acquired in different time

Imaging mechanism of underwater topography by SAR and a underwater topography SAR detection model built on the theory of underwater topography detection with SAR image presented by Yuan Yeli are used to detect the underwater topography of Shuangzi Reefs in the Nansha Islands with three scenes of SAR images acquired in different time. Detection results of three SAR images are compared with the chart topography and the detection errors are analyzed. Underwater topography detection experiments of Shuangzi Reefs show that the detection model is practicable. The detection results indicate that SAR images acquired in different time also can be used to detect the underwater topography, and the detection results are affected by the ocean conditions in the SAR acquiring time.

Wind-vector estimation for RADARSAT-1 SAR images: Validation of wind-direction estimates based upon geometry diversity

In this letter, a new wind-vector algorithm is presented that uses radar backscatter sigma(0) measurements at two adjacent subscenes of RADARSAT-1 synthetic aperture radar (SAR) images, with each subscene having slightly different geometry. Resultant wind vectors are validated using in situ buoy measurements and compared with wind vectors determined from a hybrid wind-retrieval model using wind directions determined by spectral analysis of wind-induced image streaks and observed by colocated QuikSCAT measurements. The hybrid wind-retrieval model consists of CMOD-IFR2 [applicable to C-band vertical-vertical (W) polarization] and a C-band copolarization ratio according to Kirchhoff scattering. The new algorithm displays improved skill in wind-vector estimation for RADARSAT-1 SAR data when compared to conventional wind-retrieval methodology. In addition, unlike conventional methods, the present method is applicable to RADARSAT-1 images both with and without visible streaks. However, this method requires ancillary data such as buoy measurements to resolve the ambiguity in retrieved wind direction.

海底地形的SAR影象仿真与反演

本文旨在建立SAR水下地形探测的理论和应用的基本框架。研究内容包括：1. 水下地形的SAR成象机制 采用Bragg散射理论与海面微尺度波高频谱的饱和谱形式相结合，建立了后向散射截面与海面微尺度波流调制作用间的函数关系，该函数为雷达相关项与大尺度海流对海面微尺度波的调制作用项之积，该调制项包含海底地形的信息。2. 建立水下地形的SAR影象仿真模型，定性和定量地解释SAR影象的类地形条纹以及SAR在不同的水文条件下对水下地形的可视性 以二维深度平均的海流模式或三维σ坐标的海流模式计算流场，结合风波即可计算出大尺度海流对海面微尺度波的调制作用项，文中记为函数G，并称计算所得的G值灰度影象为SAR的仿真影象。通过仿真模型可以研究不同微尺度波波向、流向及地形梯度方向情况下SAR影象对海底地形变化的可视性，结果表明，当海流流向、地形梯度方向和微尺度波波向三者平等时，SAR影象中的类地形牲的可视性最好。随着这三个方向夹角逐渐增大，可视性逐渐降低，当其中两个方向垂直时，类地形特征消失或变得很弱。较大的流速可以增强类地形影象的对比度，这在SAR影象中存在背景噪声时是重要的。3. SAR水深反演的反问题的提法与解法以及反演模型的反演精度分析通过SAR探测海底地形可以归为已知雷达后向散射截面或G值求水深的数学物理反问题，本文的反演模型由G 值函数表达式和二维深度平均的海流运动方程组以及适当的初边值条件构成。由于该反问题的边界条件的提法为超定的，所以其解设计为求目标泛涵的最小偏差解，反演算法为最速下降法。该算法不受反演大小的限制，具有较好的收剑性和解的存在性，但解依赖于初猜值的选择。当反演区域内部分点的水深已知时，这些数据可以很容易地融合在最小偏差解的算法中，从面加快收敛速度，提高计算精度。利用仿真模式所给出的SAR影象证实了该反问题的求解方法是可行的，且具有较高的计算精度。通过反演模型进行的数值试验表明： 1）微尺度波波向、流向和地形梯度方向对反演精度有明显影响。三个方向平等时反演精度最高，当其中任两向垂直时，都会成为反演的盲点。这是由反演模式本身的奇性所决定的。虽然三向夹角不同时，反演精度有变化，但在大多数情况下，反演值与真值地形波动的位置，形状和幅度等都具有很好的一致性。只有当其中两向接近垂直时，才出现较大的差异或反演失效；2）虽然一定流速的存在是反演的基础，但流速的大小对反演精度影响并不大；3）本反演系统对G值误差和反演未知量的初猜值的误差以及波向角选取误差都有较强的容差能力；但对水深边值误差较敏感，要求其精度较高；4）由于反演模式需要水深的初猜值，所以需要知道反演区域的平均水深，一个好的初猜值可以加速算法的收敛，而一个较差的初猜值则可能引起较大的误差，一船说来，平均水深就已经可以获得较高精度的结果。4. 仿真和反演模型的一个实例研究 本文以北海（the North Sea)的一张 Seasat SAR 影象和该区域的海图水深为例，采用所建立的仿真模型和反演模型对这张SAR影象上的类地形明暗条纹进行了成功的仿真，也通过SAR影象数据经过数据处理和反演，求出了影象区域的水深，反演水深数据和实际海底沙脊吻合较好。研究结果初步验证了海底地形结构的SAR影象仿真与反演的可行性。本文的研究表明，只要SAR影象在低海况下拍摄，且有精确的定位，再加上对SAR影象所覆盖海区的粗精度的水深和边界水深的已知条件，就可以在对该海区进行潮流模拟的基础上用反演模式来获取高空间分辨率的水深资料。

多源多时相SAR资料反演水下地形的同化模型

合成孔径雷达(SAR)是重要的微波传感器之一，在海洋遥感领域得到了广泛应用。浅海水下地形SAR探测是SAR海洋应用的重要部分之一，发展业务化水下地形SAR探测技术是水下地形SAR探测研究的最终目标。现有的水下地形SAR探测是基于单景SAR影像开展的，探测结果不能全面反映水下地形。因此，发展一种基于多源多时相SAR影像的水下地形反演方法是该研究方向的前沿问题。 本文基于水下地形SAR成像机制和袁业立（1997）导出的海波高频谱解析表达式，首次建立了基于多源多时相SAR影像的水下地形反演的同化模型与算法，并通过该模型在台湾浅滩水下地形SAR探测中的应用检验了该模型和算法的可行性。本文还开展了已有的浅海水下地形SAR探测技术（浅海水下地形单景SAR影像反演）在台湾浅滩水下地形探测中的应用研究，以及反演初始水深对水下地形SAR反演结果影响的研究。此外，本文还对中国近海水下地形SAR成像能力进行了分析。 在浅海水下地形SAR探测技术应用于台湾浅滩研究方面，基于7景SAR影像开展了台湾浅滩单景SAR影像反演计算，反演结果表明同一水下地形不同时相SAR影像反演结果不能全面反映真实地形特征。 在反演初始水深对水下地形SAR反演结果影响研究方面，通过不同初始水深条件下台湾浅滩水下地形SAR反演结果的比较分析，可以得出：初始水深影响水下地形反演结果的准确性，初始水深的选取需要较粗的实际水深的支持； 在多源多时相水下地形SAR反演同化模型研究方面， 建立了多源多时相水下地形SAR反演的同化模型与算法，通过基于多源多时相SAR影像的台湾浅滩五种不同情形水下地形反演计算，证明了多源多时相水下地形SAR反演同化模型和算法是可行的，并给出了基于多源多时相SAR影像的水下地形反演计算中SAR影像的选取原则。 在中国近海浅海水下地形SAR响应能力分析方面，基于对中国近海潮汐潮流状况、水下地形概况和已有中国近海SAR影像中水下地形特征等的分析，总结出中国近海适合开展浅海水下地形SAR探测的区域主要有：渤海海域、苏北近海海域、台湾海峡海域和南沙群岛海域。

C 167 INST-D 2013. 348 Muestra de diversificación del diseño de sombreros elaborados en fibras de diferentes palmas e ilustraciones de sombreros tradicionales elaborados en fibra vegetal de palma sará.

15 fotografías a color.

Correlación entre humedad del suelo y retrodispersión en imágenes SAR

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Head-SAR dependence on spectacle frame shape for operator of 450 MHz personal radio

Power deposition in the head of a user wearing metal-framed spectacles was calculated with a 450 MHz personal radio transmitting in close proximity. Peak tissue SAR in the head depended on lens shape whether circular half-rim or rectangular with 70 and 174% increases, respectively, compared to the spectacle-free case. However, localised screening occurred with square frames, with a 40% reduction of peak SAR in the eye closest to the antenna.

Synthesis and SAR of centrally active mGlu(5) positive allosteric modulators based on an aryl acetylenic bicyclic lactam scaffold

This Letter describes the hit-to-lead progression and SAR of a series of biphenyl acetylene compounds derived from an HTS screening campaign targeting the mGlu(5) receptor. 'Molecular switches' were identified that modulated modes of pharmacology, and several compounds within this series were shown to be efficacious in reversal of amphetamine induced hyperlocomotion in rats after ip dosing, a preclinical model that shows similar positive effects with known antipsychotic agents. Published by Elsevier Ltd.