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首页> 外文会议>OCEANS 2011 >Coherent and semi-coherent processing of limited-aperture circular synthetic aperture (CSAS) data
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Coherent and semi-coherent processing of limited-aperture circular synthetic aperture (CSAS) data

机译：有限孔径圆形合成孔径（CSAS）数据的相干和半相干处理

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Circular synthetic aperture sonar (CSAS) traditionally involves the coherent processing of 360 degree scattering information from acoustic targets. To obtain 360 degree scattering information, a source may circle around a central target field and constantly illuminate targets from multiple aspects. Another method of obtaining CSAS data is to fix the source location and spin a target on a rotating mount. Following data reception, a variety of methods in the Fourier or time-domain may be used to construct images. For certain targets, resonances and elastic effects can interfere with the specular portions of backscattered echoes. The time-delay associated with elastic or resonant responses destroys the uniqueness of the location to which the signal is mapped, and occasionally these resonant features can be mapped directly on top of target specular features, causing destructive interference and reduced image clarity. Destructive interference can be reduced and image clarity enhanced by incoherently summing separate images generated from sub-apertures of CSAS data. Additionally, limiting the aperture and frequency band of the pre-processed data before applying an imaging algorithm is an effective method for understanding and localizing various elastic and non-elastic target responses. In a solid 3-to-1 cylinder, for example, effects such as meridional and face-crossing rays cause well defined image features that are prominently visible when limiting the aperture to the angular portions in which these rays are the dominant elastic effects. Further analysis may be obtained by masking portions of these sub-aperture images and reversing the imaging process. This can be used to directly relate target image features to the angular frequency response (colorplot) of the target. An added benefit of this reversal process is that signals from surrounding objects, and the random noise spread throughout the image scene can be rejected by an image masking process, and the resulting ti--me-domain information has an enhanced signal-to-noise ratio. This effect has been successfully demonstrated on data acquired in field-tests, and in controlled laboratory experiments with real and replicated Unexploded Ordnance (UXO) objects. A “Projection-Slice” based CSAS script has been tested on data acquired at sea by an unmanned vehicle, as well as in laboratory experiments from UXO objects placed on a rotational mount. The laboratory based full scale UXO datasets were acquired in a controlled environment for full 360 degree aperture in a free-field configuration. The measurements were conducted at the Naval Surface Warfare Center, Panama City Division (NSWC PCD), facility T-2069 Barge Acoustic Test Facility, which has a 31.5 feet wide, 62 feet long, and 28 ft deep vinyl linear encapsulating 423,000 gallons of isothermal freshwater. The full scale targets examined included an inert 100 mm UXO target, a machined 100 mm aluminum facsimile UXO target, and a cylinder with a notch. The targets were suspended from a rotation stage, with 360 degree rotation capability, in the water column and insonified by a broadband acoustic projector. Preliminary results have also demonstrated the ability to image high-resolution circular synthetic aperture data in which the sonar platform, Remote Environmental Monitoring Units (REMUS) 600 unmanned underwater vehicle, was programmed to circle sunken objects. [Research supported by Office of Naval Research and The Strategic Environmental Research and Development Program (SERDP) under projects MM-1665 and MM-1666.]
机译：圆形合成孔径声纳（CSAS）传统上涉及对声学目标进行360度散射信息的相干处理。为了获得360度散射信息，光源可以围绕中心目标场旋转，并从多个方面不断照亮目标。获取CSAS数据的另一种方法是固定源位置，并在旋转底座上旋转目标。在数据接收之后，可以使用傅立叶或时域中的各种方法来构造图像。对于某些目标，共振和弹性效应会干扰后向散射回波的镜面部分。与弹性或共振响应相关的时间延迟会破坏信号映射到的位置的唯一性，并且有时这些共振特征可以直接映射到目标镜面特征之上，从而造成破坏性干扰并降低图像清晰度。通过对从CSAS数据的子孔径产生的独立图像进行非相干求和，可以减少破坏性干扰并提高图像清晰度。另外，在应用成像算法之前限制预处理数据的孔径和频带是一种用于理解和定位各种弹性和非弹性目标响应的有效方法。例如，在实心的3对1圆柱体中，诸如子午线和脸部交叉光线之类的效果会产生清晰的图像特征，当将孔径限制在这些射线为主要弹性效果的角部时，这些特征会明显可见。通过掩盖这些子孔径图像的部分并反转成像过程，可以获得进一步的分析。这可用于将目标图像特征直接与目标的角频率响应（色图）相关联。这种反转过程的另一个好处是，来自周围物体的信号以及散布在整个图像场景中的随机噪声可以通过图像遮罩过程来消除，从而得到的ti- -- 我域信息具有增强的信噪比。这种效果已在现场测试和受控实验室实验中使用真实和复制的未爆炸弹药（UXO）对象获得的数据中得到了成功证明。基于“ Projection-Slice”的CSAS脚本已经在无人驾驶工具在海上获取的数据上进行了测试，并在实验室实验中从放置在旋转底座上的UXO对象进行了测试。基于实验室的全面UXO数据集是在可控环境中以自由场配置获取完整360度光圈的。测量是在巴拿马市分部海军水面作战中心（NSWC PCD）的T-2069驳船声学测试设施中进行的，该设施具有31.5英尺宽，62英尺长和28英尺深的乙烯基线性封装，包封423,000加仑的等温线淡水。所检查的满刻度目标包括：惰性100 mm UXO目标，机加工的100 mm铝传真UXO目标以及带有缺口的圆柱体。将目标从具有360度旋转能力的旋转台悬吊在水柱中，并通过宽带声放映机进行声控。初步结果还显示了对高分辨率圆形合成孔径数据成像的能力，其中声纳平台，远程环境监测单元（REMUS）600无人水下航行器被编程为环绕沉没的物体。 [由海军研究办公室和战略环境研究与开发计划（SERDP）在项目MM-1665和MM-1666下支持的研究。]

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