Imaging artefacts of artificial diving waves in reverse time migration: cause analysis in the angle domain and an effective removal strategy

In areas with strong velocity gradients, traditional reverse time migration based on cross-correlation imaging condition not only produces low-frequency noise but also generates diving wave artefacts. The artefacts caused by diving waves have no typical low-frequency characteristics and cannot be eliminated by simple high-pass filtering approaches. We apply the wave-field decomposition imaging condition to analyse the causes of false images in reverse time migration by decomposing the full wave-field into up-going and down-going components in the angle domain. We find that artificial diving wave imaging artefacts, which are generated by the cross-correlation between the up-going source and down-going receiver wave-fields in areas with strong velocity gradients, arise at large angles. We propose an efficient strategy by means of the wavelength-dependent smoothing operator to eliminate artefacts from artificial diving waves in reverse time migration. Specifically, the proposed method provides more reasonable down-going wave-fields in areas with sharp velocity constructs by considering the factor of varying seismic wavelengths during wave propagation, and the artificial components of diving waves are eliminated in a straightforward manner. Meanwhile, the other wave-field components that contribute to true subsurface images are minimally affected. Benefiting from a smoothed velocity, the proposed method can be adapted to the traditional reverse time migration imaging frame, which reveals significant implementation potential for the seismic exploration industry. A salt model is designed and included to demonstrate the effectiveness of our approach.     

VSP地震干涉成像及应用研究

受井中检波器串级数局限,垂直地震剖面(VSP)反射波成像范围窄,且不能对井中最浅接收点上方区域有效成像.虽然多次波成像能扩大成像范围,但在实际应用中尚有诸多困难和挑战.本文根据Wapenaar的地震干涉理论,基于上下行波场分离技术,研发了VSP地震干涉成像方法.该方法将VSP自由表面多次波重建为在地表震源位置激发(虚震源)接收的拟地面地震反射波,然后偏移成像,以达到对多次波间接成像的目的.通过数值模型实验,测试了VSP干涉成像的极限分辨率,并讨论了主要采集参数的影响,结果表明:该方法的垂向和水平极限分辨率分别达约10m和20m,且能分辨深度达6500m处的50m×100m溶洞;采用12至24道井中检波器串采集的VSP资料,其干涉成像结果显著优于VSP反射波成像,与相应的地面地震成像效果相当.将本文方法应用于新疆地区采集的VSP资料,结果表明:与VSP反射波成像相比,成像同相轴更加连续,成像范围显著扩大;与地面地震成像相比,成像结果相当,尤其在浅中部甚至更好.新方法不仅无需进行井中接收点静校正,且能显著增大成像范围,有利于成像同相轴的追踪对比、地震属性提取和地质解释,尤其对中国新疆地区深部缝洞型储层的成像,具有广泛的实际应用前景.     

Keratose-dominated sponge grounds from temperate mesophotic ecosystems (NW Mediterranean Sea)

Differently from the North Atlantic Ocean, only few examples of sponge grounds are known from the Mediterranean Sea, mainly thriving in the deep sea. In this study, a novel temperate mesophotic ecosystem dominated by massive keratose sponges is reported from the Ligurian deep continental shelf. An extensive Remotely Operated Vehicle (ROV) survey allowed to study the structure and large-scale distribution of this biocoenosis. The sponge grounds here described are highly fragmented, being formed by a large number of dense, discrete aggregations of Sarcotragus foetidus (up to 7.7 specimens/m²) and other sponges, including Spongia lamella and Axinella polypoides. They mainly occur on flat, patchy and highly silted hardgrounds between 40 and 70 m depth. These sponge-dominated ecosystems have an exceptionally wide spatial distribution, estimated to cover up to nearly 200 hectares, with the largest sponge grounds occurring along the westernmost part of the Ligurian coast, probably in relation to more suitable oceanographic conditions. The dominant sponge species reach considerable heights (up to 65 cm), greatly increasing the habitat three-dimensionality and acting as poles of attraction for a diverse sessile and vagile fauna. In addition, the high abundance of the keratose sponge grounds at mesophotic depths might represent a larval source for shallow-water populations that in the last decades have been stricken by several mass mortality events.     

A method for vertical adjustment of digital aerial photogrammetry data by using a high-quality digital terrain model

The accuracy of vertical position information can be degraded by various sources of error in digital aerial photogrammetry (DAP) based point clouds. To address this issue, we propose a relatively straightforward method for automated correction of such point clouds. This method can be used in conjunction with any 3D reconstruction method in which a point cloud is generated from a pair of aerial images. The crux of the method involves separately co-registering each DAP point cloud (formed by the overlap of two or more images) to a common airborne laser scanning (ALS) based digital terrain model. The proposed method has the following essential steps: (1) Ground surface patches are identified in the normalized DAP point clouds by selecting areas in which standard deviation of vertical height is low, (2) height differences between the DAP and ALS point clouds are calculated at these patches, and (3) a correction surface is interpolated from these height differences and is then used to rectify the entire DAP point cloud. The performance of the proposed method is verified using plot data (n = 250) from a forested study area in Eastern Finland. We observed that DAP data from the area corrected using our proposed method resulted in significant increases in prediction accuracy of key forest variables. Specifically, the root mean squared error (RMSE) values for dominant height predictions decreased by up to 23.2%, while the associated model R² values increased by 16.9%. As for stem volume, RMSEs dropped by 20.6%, while the model R² improved by 14.6%, respectively. Hence, prediction accuracies were almost as good as with ALS data. The results suggest that vertically misaligned DAP data, if rectified using an algorithm such as the one presented here, could deliver near ALS data quality at a fraction of the cost.     

鄂尔多斯白垩系盆地地下水地球物理勘查特点和技术

从鄂尔多斯白垩系盆地地下水地球物理勘查特点出发，分析了该地区地球物理勘查所要解决的两大问题：①查明白垩系盆地地层分布特征；②进行地下水的水质判别。提出了应用频率域电磁法即Eh-4电导率成像系统解决上述两大问题的可能性，结合实例对勘查结果进行了分析，指出了Eh-4电导率成像系统勘查白垩系地层分布的合理性和进行水质判别的关键问题，认为Eh-4电导率成像系统勘查鄂尔多斯白垩系盆地地下水是合理和有效的。     

无人机载高光谱成像设备研究及应用进展

无人机载高光谱成像设备因其机动灵活、操作简单等优点,被应用于诸多研究领域,具有广泛的发展前景。本文对当前无人机载高光谱成像设备的相关研究进展进行了系统的总结和评述。首先,基于高光谱成像仪的发展过程阐述了无人机载高光谱成像设备在数据获取中的显著优势;其次,从成像方式和研究现状方面指出了目前无人机载高光谱成像设备影像幅宽窄、成本高和国产化水平低的问题,并介绍了基于无人机高光谱成像设备的最新应用研究成果,针对当前的设备缺点提出解决方案;最后,指出了无人机载高光谱成像设备的未来发展趋势。本文可为无人机载高光谱成像设备的研制提供一定的借鉴和参考,也可为基于无人机载高光谱成像设备的应用提供一定帮助。     

宽视场成像网格化算法中w-plane最优经验值研究

射电干涉阵列宽视场成像网格化处理过程中必须考虑w项的影响。w-projection和w-stacking是两种重要的宽视场成像网格化处理算法,w-plane参数是算法中影响计算速度和成图质量的一个重要因素。研究了w-projection和w-stacking两种网格化算法,利用SKA-1低频阵台站数据和ASKAP软件包进行模拟观测,对两种算法在不同w-plane参数取值情况下的成图速度和成图质量进行了定量分析对比。结果进一步表明,w-plane是性能改善的重要参数。针对w-projection算法,w-plane取值应比一般给定的经验值大才能得到较好的成像效果。w-stacking算法虽然有很大的速度优势,但算法实现中w-plane的影响更为显著,给出了推荐的w-plane取值。本文的工作是大视场成像算法的基础性研究工作,对未来平方千米阵列科学数据处理中的管线设计有较好的参考价值。     

海底地形变化对地震波场以及偏移成像的影响

本文针对海洋地球物理勘探数据处理当中偏移成像剖面中深层层位模糊,像场能量较弱的问题,从起伏海底在反射地震数据采集当中某个时刻发生变化着手,分析讨论了当海底发生微小变化以及海底发生稍大变化时模型差异对波场记录以及偏移成像剖面的影响,通过分析对比原始速度模型以及变化后速度模型同一点位上采集的波场记录以及波场记录在变化前后模型上的偏移成像剖面可以得出：不管数据采集是沿着测线方向进行还是逆着测线方向进行,对于起伏海底发生微小变化的速度模型,海底的微小变化对波场记录以及偏移剖面的影响很小;对于起伏海底发生较大变化的速度模型,海底的变化对波场记录以及偏移剖面的影响非常大。     

EH4电导率成像系统在矿产勘查中的应用

EH4电磁成像系统是一套双源型电磁法数据自动采集和处理的物探系统,它是CSAMT和MT的结合体,应用该系统对松辽盆地北部沉积盆地中与砂岩型铀矿相关的砂体的空间展布规律和断裂展布特征进行了研究,证明了EH4在矿产勘查应用中是一种行之有效的手段.     

辽宁弓长岭露天铁矿采空区探测

介绍了应用高密度电法与地震映象法对弓长岭露天铁矿采空区进行探测的方法技术及应用效果.地震映象法具有数据集速度较快、抗干扰能力强、勘探深度不受限制和资料处理速度快的特点.可根据波形特征和同相轴的形态推断异常顶部埋深.高密度电法对采空区的范围均有显示,但其受矿区游散电场的干扰较大.两种方法应相互补充,相互验证.