Common offset ground penetrating radar data inversion based on ray theory

The authors use the common offset ground penetrating radar(GPR) data inversion based on ray theory to estimate interval velocity and to obtain the relative permittivity. In the ray-tracing based inversion, the input data are the offset distance between antennas, the velocity of the first layer, the pick-up amplitude and re-ference amplitude of each reflection layer. The thickness and velocity of each layer are calculated by this recursive method. Firstly, the horizontal homogeneous layered medium model is established, and the ideal inversion results are obtained. Subsequently, Monte Carlo method is used to establish a randomly undulating homogeneous layered medium model. The common offset GPR data for the built geological model is then simulated by finite-difference time-domain(FDTD). It proved that this ray-tracing based inversion method is feasible for the horizontal layered geological model, even the layered geological model with random undulation. Undulation, represented by RMS height and CL(correlation length), influences the inversion results. Finally, a more complex geological model--pinch-out model was established. In the pinch-out model, the pinch-out interface can be clearly identified, though there is a false anomaly, which will not significantly affect the identification of the underground medium structure.     

基于IGU星历的实时卫星钟差加密方法研究

主要介绍了利用IGS提供的超快速观测星历和预报星历进行5 min和30 s实时卫星钟差获取的方法,并对利用这两种星历文件获取的卫星钟差与IGS提供的最终星历做比较,最后得出结论：基于IGS的超快速观测星历采用线性模型预报实时卫星钟差的精度高于基于IGS超快速预报星历采用三次样条函数直接内插获得的实时卫星钟差的精度,可以达到3 ns,能够满足一般实时单点定位的精度要求。     

Handling dip discrimination phenomenon in common‐reflection‐surface stack via combination of output‐imaging‐scheme and migration/demigration

In the application of a conventional common‐reflection‐surface (CRS) stack, it is well‐known that only one optimum stacking operator is determined for each zero‐offset sample to be simulated. As a result, the conflicting dip situations are not taken into account and only the most prominent event contributes to any a particular stack sample. In this paper, we name this phenomenon caused by conflicting dip problems as ‘dip discrimination phenomenon’. This phenomenon is not welcome because it not only leads to the loss of weak reflections and tips of diffractions in the final zero‐offset‐CRS stacked section but also to a deteriorated quality in subsequent migration. The common‐reflection‐surface stack with the output imaging scheme (CRS‐OIS) is a novel technique to implement a CRS stack based on a unified Kirchhoff imaging approach. As far as dealing with conflicting dip problems is concerned, the CRS‐OIS is a better option than a conventional CRS stack. However, we think the CRS‐OIS can do more in this aspect. In this paper, we propose a workflow to handle the dip discrimination phenomenon based on a cascaded implementation of prestack time migration, CRS‐OIS and prestack time demigration. Firstly, a common offset prestack time migration is implemented. Then, a CRS‐OIS is applied to the time‐migrated common offset gather. Afterwards, a prestack time demigration is performed to reconstruct each unmigrated common offset gather with its reflections being greatly enhanced and diffractions being well preserved. Compared with existing techniques dealing with conflicting dip problems, the technique presented in this paper preserves most of the diffractions and accounts for reflections from all possible dips properly. More importantly, both the post‐stacked data set and prestacked data set can be of much better quality after the implementation of the presented scheme. It serves as a promising alternative to other techniques except that it cannot provide the typical CRS wavefield attributes. The numerical tests on a synthetic Marmousi data set and a real 2D marine data set demonstrated its effectiveness and robustness.     

基于MEMS陀螺的高温随钻定向测斜仪研究

针对油气井测量时所面临的小孔径、超深井、温度范围广、温度变化率高、工作时间长等挑战, 研究了基于MEMS陀螺仪的定向测斜仪, 设计了MEMS陀螺定向测斜仪软硬件系统.为确保该环境下的测量精度提出了一种动态温度补偿方案, 并采用基于小波滤波多尺度分析的方法对动态温变环境下陀螺输出信号进行去噪滤波处理, 以实现定向测斜仪系统的测量精度.论文给出了定向测斜仪硬件系统方案、定向测斜算法、小波多尺度滤波算法.测试结果表明: 该系统在常温和动态温变环境下井斜方位角精度优于±2°, 井斜角精度优于±0.1°, 工作温度最高150 ℃, 可适应我国深层油气井勘探开发的应用场景需求.

     

3S技术评估独立坐标系适用范围的方法

首先讨论了城市独立坐标系的变换规律以及距离改正和变形改正的相关算法;然后利用遥感、地理信息等3S技术,精确计算重庆城市独立坐标系的适用范围,为城市独立坐标系的建设和改进提供了可靠地理论支撑。     

利用星地双向伪距数据进行钟差预报分析

给出了星地双向上下行伪距观测的数学模型。利用Compass-M1卫星2007-11-25~2007-11-30的实测数据进行了钟差计算,并利用计算结果分别采用3种方案进行了短期、长期钟差预报。总结了钟差预报精度随拟合时间的变化规律,分析了其产生的原因,并给出了有益的结论。     

3D Surface velocity retrieval of mountain glacier using an offset tracking technique applied to ascending and descending SAR constellation data: a case study of the Yiga Glacier

COSMO-SkyMed is a constellation of four X-band high-resolution radar satellites with a minimum revisit period of 12 hours. These satellites can obtain ascending and descending synthetic aperture radar (SAR) images with very similar periods for use in the three-dimensional (3D) inversion of glacier velocities. In this paper, based on ascending and descending COSMO-SkyMed data acquired at nearly the same time, the surface velocity of the Yiga Glacier, located in the Jiali County, Tibet, China, is estimated in four directions using an offset tracking technique during the periods of 16 January to 3 February 2017 and 1 February to 19 February 2017. Through the geometrical relationships between the measurements and the SAR images, the least square method is used to retrieve the 3D components of the glacier surface velocity in the eastward, northward and upward directions. The results show that applying the offset tracking technique to COSMO-SkyMed images can be used to derive the true 3D velocity of a glacier’s surface. During the two periods, the Yiga Glacier had a stable velocity, and the maximum surface velocity, 2.4?m/d, was observed in the middle portion of the glacier, which corresponds to the location of the steepest slope.     

Flume experiments on the horizontal stream offset by strike‐slip faults

Flume experiments, in which the middle section of an erosion channel is displaced horizontally, have been conducted to assess the response of streams to horizontal displacement by a strike‐slip fault. The experimental erosion channel was developed in a mixture of sand and clay, which provided relatively stable banks with its cohesiveness. Horizontal displacement of a strike‐slip fault perpendicular to the channel is expected to add a ?at section to its longitudinal pro?le along the fault line. The experimental stream eliminated this ?at section with downstream degradation, upstream aggradation, and lateral channel shift. As a result, a roughly continuous longitudinal pro?le was maintained. This maintenance of a continuous longitudinal pro?le along channel is considered to be the principle of stream response to horizontal displacement by a strike‐slip fault. Downstream degradation was the dominant process of this stream response in the overall tendency of erosion without sand supply. When the rate of fault displacement was low (long recurrence interval), the experimental stream eroded the fault surface, jutting laterally into the channel like a scarp, and de?ected the channel within the recurrence interval. This lateral channel shift gave some gradient to the reach created by fault displacement (offset reach), and the downstream degradation occurred as much as completing the remaining longitudinal pro?le adjustment. When the rate of fault displacement was high (short recurrence interval), the lateral erosion on the ?rst fault surface was interrupted by the next fault displacement. The displacement was then added incrementally to the existing channel offset making channel shift by lateral erosion increasingly dif?cult. The channel offset with sharp bends persisted without much modi?cation, and downstream degradation and upstream aggradation became evident with the effect of the offset channel course, which worked like a dam. In this case, a slight local convexity, which was incidentally formed by downstream degradation and upstream aggradation, tended to remain in the roughly continuous longitudinal pro?le, as long as the horizontal channel offset persisted. In either case, once the experimental stream obtained a roughly continuous gradient, further channel adjustment seemed to halt. Horizontal channel offset remained to a greater or lesser extent at the end of each run long after the last fault displacement. Copyright © 2004 John Wiley & Sons, Ltd.     

PSP总日射表灵敏度系数的热偏移订正方法

PSP总日射表在我国一直作为标准总日射表和质量优良的辐射仪器在使用,2006年以前还曾作为国家散射标准,在太阳辐射量值传递中测量标准散射辐射,通过成分和法计算标准总日射辐照度。总日射表的校准在晴天条件下进行,此时天空无云,由于热偏移为负值,导致对短波灵敏度系数被低估。2011年10月14日—11月15日在北京密云上甸子大气本底站进行了对比观测试验,通过对不同总日射表热偏移订正方法的试验与研究,进行了5种热偏移订正方法的比较。通过订正,在用于室外成分和法校准时,PSP表的灵敏度系数的准确度可提高1%,进而提高总辐射的测量准确度。     

几种精密卫星钟差加密方法的比较与分析

卫星钟差是影响GPS高精度单点定位的一个重要因素,通过分析几种加密GPS精密卫星钟差的方法,将加密结果与GFZ(German Research Centre for Geosciences)提供的数据进行比较,并通过精度分析,得出分段线性插值法是加密GPS精密卫星钟差一种较为可靠的方法。