全文获取类型
| 收费全文 | 70篇 |
| 免费 | 13篇 |
| 国内免费 | 1篇 |
专业分类
| 测绘学 | 29篇 |
| 大气科学 | 10篇 |
| 地球物理 | 28篇 |
| 地质学 | 7篇 |
| 海洋学 | 7篇 |
| 天文学 | 1篇 |
| 自然地理 | 2篇 |
出版年
| 2022年 | 1篇 |
| 2021年 | 1篇 |
| 2018年 | 1篇 |
| 2017年 | 3篇 |
| 2016年 | 2篇 |
| 2015年 | 1篇 |
| 2014年 | 2篇 |
| 2013年 | 6篇 |
| 2012年 | 4篇 |
| 2011年 | 4篇 |
| 2010年 | 2篇 |
| 2009年 | 5篇 |
| 2008年 | 4篇 |
| 2007年 | 9篇 |
| 2006年 | 5篇 |
| 2005年 | 3篇 |
| 2004年 | 3篇 |
| 2003年 | 1篇 |
| 2002年 | 1篇 |
| 2001年 | 4篇 |
| 2000年 | 4篇 |
| 1999年 | 6篇 |
| 1998年 | 2篇 |
| 1996年 | 1篇 |
| 1994年 | 1篇 |
| 1993年 | 1篇 |
| 1992年 | 3篇 |
| 1991年 | 2篇 |
| 1990年 | 1篇 |
| 1989年 | 1篇 |
排序方式： 共有84条查询结果，搜索用时 93 毫秒
31.
Suppression of near‐surface scattered body‐to‐surface waves: a steerable and nonlinear filtering approach 
下载免费PDF全文
下载免费PDF全文 M. Nafi Toksöz 《Geophysical Prospecting》2016,64(2):392-405
We present an approach based on local‐slope estimation for the separation of scattered surface waves from reflected body waves. The direct and scattered surface waves contain a significant amount of seismic energy. They present great challenges in land seismic data acquisition and processing, particularly in arid regions with complex near‐surface heterogeneities (e.g., dry river beds, wadis/large escarpments, and karst features). The near‐surface scattered body‐to‐surface waves, which have comparable amplitudes to reflections, can mask the seismic reflections. These difficulties, added to large amplitude direct and back‐scattered surface (Rayleigh) waves, create a major reduction in signal‐to‐noise ratio and degrade the final sub‐surface image quality. Removal of these waves can be difficult using conventional filtering methods, such as an filter, without distorting the reflected signal. The filtering algorithm we present is based on predicting the spatially varying slope of the noise, using steerable filters, and separating the signal and noise components by applying a directional nonlinear filter oriented toward the noise direction to predict the noise and then subtract it from the data. The slope estimation step using steerable filters is very efficient. It requires only a linear combination of a set of basis filters at fixed orientation to synthesize an image filtered at an arbitrary orientation. We apply our filtering approach to simulated data as well as to seismic data recorded in the field to suppress the scattered surface waves from reflected body waves, and we demonstrate its superiority over conventional techniques in signal preservation and noise suppression. 相似文献
32.
朱立志 《测绘与空间地理信息》2012,35(11):103-105
作为直接获取对象表面点3维坐标的现代对地观测技术,激光雷达技术能够快速获取高精度地面高程模型。基于LiDAR系统所获取的点云数据,通过过滤处理将区域纯地形特征信息与地物信息相分离,最终生成高精度的DEM,并在此基础上对同步获取的数码影像进行正射纠正,为进一步的信息提取、定量分析及实体建模奠定基础。 相似文献
33.
Autoregressive filtering versus linear detrending in estimation of fluxes by the eddy covariance method 总被引：10，自引：7，他引：3
The application of autoregressive running mean filtering (RMF) and linear detrending (LDT) in the estimation of turbulent fluxes by the eddy covariance method is analysed. The systematic, as well as the random, errors of the fluxes arising from filtering and/or limited observation time effects are described. To observe negligible systematic errors in fluxes, the RMF has to be applied with moderately long time constants. However, the obtained flux values are subject to increased random errors during periods of non-stationarity and the method leads to systematic overestimation of variances. These shortcomings are not inherent in the LDT approach, which is recommended for use. But the systematic errors of fluxes due to LDT are not negligible under certain experimental conditions and have to be accounted for. The corrections are important because the relatively small errors in short-period fluxes can translate to significant errors in long-period averages. The corrections depend on the turbulence time scales, which should be preferably estimated as ensemble mean variables for a particular site. 相似文献
34.
Atmospheric modelling in GPS analysis and its effect on the estimated geodetic parameters 总被引：4，自引：2，他引：2
Permanently operating Global Positioning System (GPS) receivers are used today, for example, in precise positioning and determination
of atmospheric water vapour content. The GPS signals are delayed by various gases when traversing the atmosphere. The delay
due to water vapour, the wet delay, is difficult to model using ground surface data and is thus often estimated from the GPS
data. In order to obtain the most accurate results from the GPS processing, a modelling of the horizontal distribution of
the wet delay may be necessary. Through simulations, three such models are evaluated, one of which is developed in this paper.
In the first model the water vapour is assumed to be horizontally stratified, thus the wet delay can be described by only
one zenith parameter. The second model gives the wet delay with one zenith and two horizontal gradient parameters. The third
model uses the correlation between the wet-delay values in different directions. It is found that for large gradients and
strong turbulence the two latter models yield lower errors in the estimated vertical coordinate and wet-delay parameters.
For large gradients this improvement is up to 7 mm in the zenith wet-delay parameter, from 9 mm down to 2 and 4 mm for the
second and third models, respectively.
Received: 7 May 1998 / Accepted: 1 March 1999 相似文献
35.
The present paper looks at algorithms to be implemented in the software of bottom pressure recorders (BPRs) for the automatic, real-time detection of a tsunami within recorded signals. The structure of an algorithm based on the use of an artificial neural network (ANN) is presented and compared to the one developed under the Deep-ocean Assessment and Reporting of Tsunamis (DART) program run by the U.S. National Oceanic and Atmospheric Administration (NOAA). The performance and efficiency of the two algorithms are compared using both synthetic and actually measured time series. Results show that an improvement in detection performance can be obtained by using the ANN algorithm. 相似文献
36.
以自动生成测地线活动轮廓(geodesic active contour,GAC)模型的初始曲线及改进其外力为出发点,提出一种基于LiDAR点云和随机影像数据,利用改进的GAC模型进行建筑物边界提取的方案。首先利用形态学交替序贯滤波自动获得模型演化的初始曲线;进而利用LiDAR深度梯度影像改进模型演化的外力,得到了改进的测地线活动轮廓(improved geodesic active contour,IGAC)模型。仿真试验表明,采用IGAC模型,可抑制弱边界泄漏,并提高建筑物边界提取的完整性和形状精确度。 相似文献
37.
GOCE卫星提供的梯度数据含有非常大的低频误差,如何处理这种误差是GOCE数据处理中最为关键的工作之一.本文根据GOCE卫星的运行情况,首先分析了梯度数据的频率特性,推导了频率与阶次的对应关系;并在此之上,介绍了针对低频误差的滤波方法,即移去恢复和向前向后滤波方法,前者可解决滤波中的低频信号损失问题,后者则主要解决了滤波中的相位漂移问题.最终结果表明:引力梯度的时间频谱与球谐展开中的阶次虽不是一一对应的,但各阶所对应的最大截止频率与阶次却有一定的显式表达.同时也表明,本文所采用的滤波方法是有效的,达到了消除低频误差但保留观测频段信号的目的. 相似文献
38.
Length-of-day (LOD) estimates from seven Global Positioning System (GPS) and three satellite laser ranging (SLR) analysis
centers were combined into an even-spaced time series for a 27-month period (1996–1998). This time series was compared to
the multi-technique Earth-orientation-parameter (EOP) combined solution (C04) derived at the Central Bureau of the International
Earth Rotation Service (IERS/CB). Due to inhomogeneities in the different series derived from the various techniques (time,
length, quality, and spatial resolution), the concept of a combined solution is justified. The noise behavior in LOD for different
techniques varies with frequency; the data series were divided into frequency windows after removing both biases and trends.
Different weight factors were assigned in each window, discriminating by technique, and produced one-technique combined solutions.
Finally, these one-technique combined solutions were combined to obtain the final multi-technique solution. The LOD combined
time series obtained by the present method based on the frequency windows combined series (FWCS) is very close to the IERS
C04 solution. It could be useful to generate a new LOD reference time series to be used in the study of high-frequency variations
of Earth rotation.
Received: 28 March 2000 / Accepted: 15 February 2001 相似文献
39.
M. N. French R. L. Bras W. F. Krajewski 《Stochastic Environmental Research and Risk Assessment (SERRA)》1992,6(1):27-45
A procedure for short-term rainfall forecasting in real-time is developed and a study of the role of sampling on forecast ability is conducted. Ground level rainfall fields are forecasted using a stochastic space-time rainfall model in state-space form. Updating of the rainfall field in real-time is accomplished using a distributed parameter Kalman filter to optimally combine measurement information and forecast model estimates. The influence of sampling density on forecast accuracy is evaluated using a series of a simulated rainfall events generated with the same stochastic rainfall model. Sampling was conducted at five different network spatial densities. The results quantify the influence of sampling network density on real-time rainfall field forecasting. Statistical analyses of the rainfall field residuals illustrate improvement in one hour lead time forecasts at higher measurement densities. 相似文献
40.