排序方式: 共有28条查询结果,搜索用时 15 毫秒
1.
2.
3.
光滑处理使得单界面成为非均匀薄层,界面反射转变为层反射.为了探讨光滑处理的影响,以平面波作为入射波场,首先利用过渡层反射系数推导了反射信号的理论公式,然后就非均匀薄层下反射系数的计算问题,给出了具体的实现算法,并通过与经典Epstein过渡层反射系数解析结果的对比说明了算法的精度.最后在单界面及其被光滑后界面的对比分析中,得出了几点重要结论:随着光滑次数的增加,反射信号的到时基本保持不变,而反射信号的主频与能量呈减少趋势,其中信号能量在低光滑次数的衰减速率明显大于高光滑次数. 相似文献
4.
合成孔径雷达 (SAR)图像一般都存在相干噪声 ,对地物信息的提取及 SAR图像应用的干扰非常严重 ,对此许多人提出了不少处理方法 ,并分析对比了多种滤波算法 ,认为改良 K -均值自适应滤波效果最佳。本文中分析了改良 K -均值自适应滤波法的数学基础的局限性 ,并采用了一种基于多分辨分析的滤波算法 ,该算法通过将噪声 (或较小的结构特征 )与较大的结构特征相分离 ,然后滤出噪声 (或较小的结构特征 ) ,从而达到消除斑点噪声的目的。实验结果证明 ,基于多分辨分析的滤波算法在消除 SAR图像的斑点噪声方面优于改良 K -均值自适应滤波法。 相似文献
5.
6.
本文主要介绍一种利用TMS 32010数字信号处理器(DSP)和IBM-PC/XT微机构成的微机遥感图像快速处理系统。在此系统上,我们根据微波遥感图像的特点,采用TMS32010宏汇编语言研制出了一个遥感图像快速处理软件库。经过机载微波辐射计图像处理检验,采用TMS 32010语言编程在该系统上的图像处理速度要比采用FORTRAN语言编程在普通微机系统上的图像处理速度提高了100-500倍。此外,本文还提出一种新的平滑滤波算法。该算法滤除高斯白噪声的能力要优于中值滤波,同时还可以保护图像的边缘不被模糊。 相似文献
7.
Reconstructed sunspot data are available that extend solar activity back to 11 360 years before the present. We have examined
these data using Hurst analysis, a moving average filter, and Fourier analysis. All of the procedures indicate the presence
of a long term (≈6 000 year) cycle not previously reported. A number of shorter cycles formerly identified in the literature
by using Fourier analysis, Bayes methods, and maximum entropy methods were also detected in the reconstructed sunspot data. 相似文献
8.
D. S.?MaglioneEmail author A. M.?Diblasi 《Stochastic Environmental Research and Risk Assessment (SERRA)》2004,18(6):366-376
The variogram is one of the most important tools in the assessment of spatial variability and a crucial parameter for kriging. It is widely known that an estimator for the variogram cannot be used as its representator in some contexts because of its lack of conditional semi negative definiteness. Consequently, once the variogram is estimated, a valid family must be chosen to fit an appropriate model. Under isotropy, this selection is carried out by eye from the observation of the variogram estimated curve. In this paper, a statistical methodology is proposed to explore a valid model for the variogram. The statistic for this approach is based on quadratic forms depending on smoothed random variables which gather the underlying spatial variation. The distribution of the test statistic is approximated by a shifted chi-square distribution. A simulation study is also carried out to check the power and size of the test. Reference bands, as a complementary graphical tool, are calculated. An example from the literature is used to illustrate the methodologies presented. 相似文献
9.
The adoption of new cropping practices such as integrated Crop-Livestock systems (iCL) aims at improving the land use sustainability of the agricultural sector in the Brazilian Amazon. The emergence of such integrated systems, based on crop and pasture rotations over and within years, challenges the remote sensing community who needs to implement accurate and efficient methods to process satellite image time series (SITS) in order to come up with a monitoring protocol. These methods generally include a SITS preprocessing step which can be time consuming. The aim of this study is to assess the importance of preprocessing operations such as temporal smoothing and computation of phenological metrics on the mapping of main cropping systems (i.e. pasture, single cropping, double cropping and iCL), with a special emphasis on the iCL class. The study area is located in the state of Mato Grosso, an important producer of agriculture commodities located in the Southern Brazilian Amazon. SITS were composed of a set of 16-day composites of MODIS Vegetation Indices (MOD13Q1 product) covering a one year period between 2014 and 2015. Two widely used classifiers, i.e. Random Forest (RF) and Support Vector Machine (SVM), were tested using five data sets issued from a same SITS but with different preprocessing levels: (i) raw NDVI; (ii) raw NDVI + raw EVI; (iii) smoothed NDVI; (iv) NDVI-derived phenometrics; (v) raw NDVI + phenometrics. Both RF and SVM classification results showed that the “raw NDVI + raw EVI” data set achieved the highest performance (RF OA = 0.96, RF Kappa = 0.94, SVM OA = 0.95, SVM Kappa = 0.93), followed closely by the “raw NDVI” and the “raw NDVI + phenometrics” datasets. The “NDVI-derived phenometrics” alone achieved the lowest accuracies (RF OA = 0.58 and SVM OA = 0.66). Considering that the implementation of preprocessing steps is computationally expensive and does not provide significant gains in terms of classification accuracy, we recommend to use raw vegetation indices for mapping cropping practices in Mato Grosso, including the integrated Crop-Livestock systems. 相似文献
10.
Approximate decorrelation and non-isotropic smoothing of time-variable GRACE-type gravity field models 总被引:6,自引:1,他引:6
Jürgen Kusche 《Journal of Geodesy》2007,81(11):733-749
We discuss a new method for approximately decorrelating and non-isotropically filtering the monthly gravity fields provided
by the gravity recovery and climate experiment (GRACE) twin-satellite mission. The procedure is more efficient than conventional
Gaussian-type isotropic filters in reducing stripes and spurious patterns, while retaining the signal magnitudes. One of the
problems that users of GRACE level 2 monthly gravity field solutions fight is the effect of increasing noise in higher frequencies.
Simply truncating the spherical harmonic solution at low degrees causes the loss of a significant portion of signal, which
is not an option if one is interested in geophysical phenomena on a scale of few hundred to few thousand km. The common approach
is to filter the published solutions, that is to convolve them with an isotropic kernel that allows an interpretation as smoothed
averaging. The downside of this approach is an amplitude bias and the fact that it neither accounts for the variable data
density that increases towards the poles where the orbits converge nor for the anisotropic error correlation structure that
the solutions exhibit. Here a relatively simple regularization procedure will be outlined, which allows one to take the latter
two effects into account, on the basis of published level 2 products. This leads to a series of approximate decorrelation
transformations applied to the monthly solutions, which enable a successive smoothing to reduce the noise in the higher frequencies.
This smoothing effect may be used to generate solutions that behave, on average over all possible directions, very close to
Gaussian-type filtered ones. The localizing and smoothing properties of our non-isotropic kernels are compared with Gaussian
kernels in terms of the kernel variance and the resulting amplitude bias for a standard signal. Examples involving real GRACE
level 2 fields as well as geophysical models are used to demonstrate the techniques. With the new method, we find that the
characteristic striping pattern in the GRACE solutions are much more reduced than Gaussian-filtered solutions of comparable
signal amplitude and root mean square. 相似文献