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61.
南设得兰群岛位于德雷克海峡南侧, 南经布兰斯菲尔德海峡与南极半岛相望。该区域一直是南大洋海洋学研究的热点区域, 近些年已成为南极磷虾渔业的重要作业区。透光层作为海洋生物活动最为集中的区域, 也是海洋中生产力最为丰富的区域。了解透光层水团的特性及变化, 一方面可为南极半岛海洋学研究提供基础信息, 同时也可为南极磷虾等中上层海洋生物的分布及其致因提供科学支撑。通过分析2013年1月至3月南设得兰群岛周边海域5个断面的透光层温、盐数据, 本研究梳理了该区域的水团属性和分布。结果显示, 南设得兰群岛北侧较深水区水团垂向结构明显, 由上至下依次为南极夏季表层水、冬季水和绕极深层水。位于南设得兰群岛南侧的布兰斯菲尔德海峡内, 威德尔海过渡水特征几乎占据了整个布兰斯菲尔德海峡。但布兰斯菲尔德海峡西南侧水团结构较为复杂, 包括了威德尔海过渡水、别林斯高晋海过渡水和德雷克海峡水等。阐明南设得兰群岛周边复杂的水团结构对于进一步开展南大洋生物-物理相互作用研究具有重要的科学意义。 相似文献
62.
ShiQiao Zhou 《寒旱区科学》2020,12(6):430-435
Tibetan lake levels are sensitive to global change, and their variations have a large impact on the environment, local agriculture and animal husbandry practices. While many remote sensing data of Tibetan lake level changes have been reported, few are from in-situ measurements. This note presents the first in-situ lake level time series of the central Tibetan Plateau. Since 2005, daily lake level observations have been performed at Lake Nam Co, one of the largest on the Tibetan Plateau. The interannual lake level variations show an overall increasing trend from 2006 to 2014, a rapid decrease from 2014 to 2017, and a surge from 2017 to 2018. The annual average lake level of the hydrological year (May-April) rose 66 cm from 2006 to 2014, dropped 59 cm from 2014 to 2017, and increased 20 cm from 2017 to 2018, resulting in a net rise of 27 cm or an average rate of about 2 cm per year. Compared to the annual average lake level based on the calendar year, it is better to use the annual average lake level based on the hydrological year to determine the interannual lake level changes. As the lake level was stable in May, it is appropriate to compare May lake levels when examining interannual lake level changes with fewer data. Overall, remote sensing results agree well with the in-situ lake level observations; however, some significant deviations exist. In the comparable 2006-2009 period, the calendar-year average lake level observed in-situ rose by 10-11 cm per year, which is lower than the ICESat result of 18 cm per year. 相似文献
63.
Feasibility of signal enhancement with multiple grounded‐wire sources for a frequency‐domain electromagnetic survey 下载免费PDF全文
Haigen Zhou Yao Yao Changsheng Liu Jun Lin Lili Kang Gang Li Xinsen Zeng 《Geophysical Prospecting》2018,66(4):818-832
Frequency‐domain electromagnetic methods with a grounded‐wire source are powerful tools in geophysical exploration. However, the signal may be too weak to guarantee the quality of survey data in complex electromagnetic environments, especially when the receiver is located in the air for the newly developed grounded‐source airborne frequency‐domain electromagnetic method. In this paper, a signal enhancement method with multiple sources is proposed to solve this problem. To evaluate the signal enhancement effect, we compared the signals generated by a single source and multiple sources with equal electric moment. The signal differences caused by synchronisation error and separation distance between source elements were analysed, and the methods to achieve maximum signal were introduced. Besides, we discussed the interaction between adjacent source elements to ensure the system safety, including the changes in output current and the safe distance between two sources using a dual‐source model. Lastly, a comprehensive field experiment was designed and conducted to test the multiple‐source method. The data processing results are comparable for single and dual sources, and the signal‐to‐noise ratio of dual source is higher in the field test. The subsurface resistivity structure at the test site is consistent with the previous controlled‐source audio‐frequency magnetotellurics method. These results show that signal enhancement with multiple sources is feasible. This study provides guidance to the application of multiple sources in field surveys when the survey environment is complex and rigorous. 相似文献
64.
Ordos block was squeezed by the Qinghai-Tibetan block and North China block, and the tectonic activity was intense. In the periphery of Ordos block, there was a series of folds zones and compressed faults with complicate structures. This paper used three-phase data of 1980,1990 and 2014 to calculate vertical velocity of Northwestern margin of Ordos and the analytical results indicated that ① the Hetao basin between the rise of Yinshan fault block and Ordos fault block showed relatively subsidence, in which Linhe basin was the most evident and the subsidence rate was about 2-4mm/a. The subsidence rate of Jartai -Yinchuan rift zone on the western margin of Ordos block was about 2mm/a; ② the whole testing zone exhibited the evident inherited movement characterized by mountain rise and basin subsidence; ③the two leveling section through the northern margin fault and Dengkou-Benjing fault showed that the difference between vertical velocities on two sides of the fault was less than 0.5mm/a. 相似文献
65.
声反射成像测井中常用的基于射线理论的Kirchhoff积分偏移算法和基于单程波理论的F-K偏移算法均可实现井旁缝洞反射体的快速偏移成像,但其仅适用于地层垂向变化较弱的速度场和高陡角裂缝的偏移成像,无法实现低角度反射体的准确偏移归位,产生偏移假象误导测井解释.逆时偏移基于全波动方程,可适应强垂向变化速度场,实现近似水平反射体的偏移成像.本文详细分析了将逆时偏移应用于声反射成像测井时存在的数据准备、时间采样间隔匹配和成像条件改进等若干问题,通过设置多组理论模型来说明算法对井旁不同反射体的识别能力.模拟资料和实际资料处理结果证实,较F-K偏移算法,逆时偏移算法成像精度更高、收敛性更好,可有效实现近似水平构造偏移归位.改进的归一化互相关成像条件可解决深部地层的远井壁成像衰减问题,降低测井解释的多解性.逆时偏移将成为声反射成像测井高精度偏移技术的发展方向. 相似文献
66.
微型近红外光谱仪测量北极积雪覆盖海冰内部太阳辐照度可行性研究 总被引:1,自引:1,他引:0
The extremely low temperature, high humidity and limited power supply pose considerable challenges when using spectrometers within the Arctic sea ice. The feasibility of using a miniature low-power near-infrared spectrometer module to measure solar radiation in Arctic sea ice environments was investigated in this study.Temperature and integration time dependences of the spectrometer module were examined over the entire target operating range of –50℃ to 30℃, well below the specified operating range of this spectrometer. Using these observations, a dark output prediction model was developed to represent dark output as a function of temperature and integration time. Temperature-induced biases in the saturation output and linear operating range of the spectrometer were also determined. Temperature and integration time dependences of the signal output were evaluated. Two signal output correction models were developed and compared, to convert the signal output at any temperature within the operating temperature range and integration time to that measured at the reference temperature and integration time. The overall performance of the spectrometer was evaluated by integrating it into a refined fiber optic spectrometry system and measuring solar irradiance distribution in the ice cover with thickness of 1.85 m in the Arctic during the 9th Chinese National Arctic Research Expedition. The general shape of the measured solar irradiance above the snow surface agreed well with that measured by other commercial oceanographic spectroradiometers. The measured optical properties of the sea ice were generally comparable to those of similar ice measured using other instruments. This approach provides a general framework for assessing the feasibility of using spectrometers for applications in cold environments. 相似文献
67.
We analyzed seafloor morphology and geophysical anomalies of the Southeast Indian Ridge(SEIR) to reveal the remarkable changes in magma supply along this intermediate fast-spreading ridge. We found systematic differences of the Australian-Antarctic Discordance(AAD) from adjacent ridge segments with the residual mantle Bouguer gravity anomaly(RMBA) being more positive, seafloor being deeper, morphology being more chaotic, M factors being smaller at the AAD. These systematic anomalies, as well as the observed Na_(8.0) being greater and Fe_(8.0) being smaller at AAD, suggest relatively starved magma supply and relatively thin crust within the AAD.Comparing to the adjacent ridges segments, the calculated average map-view M factors are relatively small for the AAD, where several Oceanic Core Complexes(OCCs) develop. Close to 30 OCCs were found to be distributed asymmetrically along the SEIR with 60% of OCCs at the northern flank. The OCCs are concentrated mainly in Segments B3 and B4 within the AAD at ~124°–126°E, as well as at the eastern end of Zone C at ~115°E. The relatively small map-view M factors within the AAD indicate stronger tectonism than the adjacent SEIR segments.The interaction between the westward migrating Pacific mantle and the relatively cold mantle beneath the AAD may have caused a reduction in magma supply, leading to the development of abundant OCCs. 相似文献
68.
An enhanced approach for surface flow routing over drainage‐constrained triangulated irregular networks 下载免费PDF全文
The accuracy and efficiency of the simulations in distributed hydrological models must depend on the proper estimation of flow directions and paths. Numerous studies have been carried out to delineate the drainage patterns based on gridded digital elevation models (DEMs). The triangulated irregular network (TIN) has been increasingly applied in hydrological applications due to the advantages of high storage efficiency and multi‐scale adaptive performance. Much of the previous literature focuses mainly on filling the depressions on gridded DEMs rather than treating the special cases in TIN structures, which has hampered its applications to hydrological models. This study proposes a triangulation‐based solution for the removal of flat areas and pits to enhance the simulation of flow routing on triangulated facet networks. Based on the drainage‐constrained TIN generated from only a gridded DEM by the compound point extraction (CPE) method, the inconsistent situations including flat triangles, V‐shape flat edges and sink nodes are respectively identified and rectified. The optimization algorithm is an iterative process of TIN reconstruction, in which the flat areas are generalized into their center points and the pits are rectified by embedding break lines. To verify the proposed algorithm and investigate the potential for flow routing, flow paths of steepest descent are derived by the vector‐based tracking algorithm based on the optimized TIN. A case study of TIN optimization and flow path tracking was performed on a real‐world DEM. The outcomes indicate that the proposed approach can effectively solve the problem of inconsistencies without a significant loss in accuracy of the terrain model. 相似文献
69.
Although alteration minerals related to metallogenesis is very important in mineral exploration, information of alteration mineral is weakly expressed in remote sensing imagery, which is often subject to interfering noise and sometimes limited in spectral and spatial resolutions. Because of easy access, moderate images are the main sources of alteration mineral information. Therefore, it is very important to develop alteration mineral information extraction methods from remote sensing images. In this paper, a combined method based on Mask, principal component analysis (PCA) and support vector machine method (SVM) was used to extract alteration mineral information from Enhanced thematic mapper plus remote sensing data with limited spectral and spatial resolutions. First, a mask image of the remote sensing imagery was created to remove interference information such as vegetation, shadow and water. Then, PCA was employed to collect sample data relating to iron, argillic, and carbonatization alteration. Finally, SVM was used to deal with alteration anomaly and build a feature extraction model of high accuracy. The Mask-PCA-SVM model is used to extract alteration mineral information from remote sensing images of Hatu area, Xinjiang Uygur Autonomous Regions, China. The results show that the new methods proposed in this paper can coincide well with known deposits occurrences, rate reached 86.51%. While, the consistent rate with known deposits of the ratio model, PCA model and Spectral angle mapper model were only 3.37, 65.08 and 69.05% respectively. This suggests that the proposed model can find the actual distribution of mineral deposits more effectively by reducing interference to a greater degree. 相似文献
70.
Initial results of centralized autonomous orbit determination of the new-generation BDS satellites with inter-satellite link measurements 总被引:3,自引:0,他引:3
Chengpan Tang Xiaogong Hu Shanshi Zhou Li Liu Junyang Pan Liucheng Chen Rui Guo Lingfeng Zhu Guangming Hu Xiaojie Li Feng He Zhiqiao Chang 《Journal of Geodesy》2018,92(10):1155-1169
Autonomous orbit determination is the ability of navigation satellites to estimate the orbit parameters on-board using inter-satellite link (ISL) measurements. This study mainly focuses on data processing of the ISL measurements as a new measurement type and its application on the centralized autonomous orbit determination of the new-generation Beidou navigation satellite system satellites for the first time. The ISL measurements are dual one-way measurements that follow a time division multiple access (TDMA) structure. The ranging error of the ISL measurements is less than 0.25 ns. This paper proposes a derivation approach to the satellite clock offsets and the geometric distances from TDMA dual one-way measurements without a loss of accuracy. The derived clock offsets are used for time synchronization, and the derived geometry distances are used for autonomous orbit determination. The clock offsets from the ISL measurements are consistent with the L-band two-way satellite, and time–frequency transfer clock measurements and the detrended residuals vary within 0.5 ns. The centralized autonomous orbit determination is conducted in a batch mode on a ground-capable server for the feasibility study. Constant hardware delays are present in the geometric distances and become the largest source of error in the autonomous orbit determination. Therefore, the hardware delays are estimated simultaneously with the satellite orbits. To avoid uncertainties in the constellation orientation, a ground anchor station that “observes” the satellites with on-board ISL payloads is introduced into the orbit determination. The root-mean-square values of orbit determination residuals are within 10.0 cm, and the standard deviation of the estimated ISL hardware delays is within 0.2 ns. The accuracy of the autonomous orbits is evaluated by analysis of overlap comparison and the satellite laser ranging (SLR) residuals and is compared with the accuracy of the L-band orbits. The results indicate that the radial overlap differences between the autonomous orbits are less than 15.0 cm for the inclined geosynchronous orbit (IGSO) satellites and less than 10.0 cm for the MEO satellites. The SLR residuals are approximately 15.0 cm for the IGSO satellites and approximately 10.0 cm for the MEO satellites, representing an improvement over the L-band orbits. 相似文献