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91.
CHEN Luyao YUE Jianwei JIANG Weiguo LI Jing CHEN Yunhao 《地球空间信息科学学报》2007,10(4):299-302
The unceasing change problem of land information systems can be resolved through the refactoring and design pattern. To promote the implementation of design pattern and refactoring methods in developin... 相似文献
92.
Accurate upward continuation of gravity anomalies supports future precision, free-inertial navigation systems, since the latter
cannot by themselves sense the gravitational field and thus require appropriate gravity compensation. This compensation is
in the form of horizontal gravity components. An analysis of the model errors in upward continuation using derivatives of
the standard Pizzetti integral solution (spherical approximation) shows that discretization of the data and truncation of
the integral are the major sources of error in the predicted horizontal components of the gravity disturbance. The irregular
shape of the data boundary, even the relatively rough topography of a simulated mountainous region, has only secondary effect,
except when the data resolution is very high (small discretization error). Other errors due to spherical approximation are
even less important. The analysis excluded all measurement errors in the gravity anomaly data in order to quantify just the
model errors. Based on a consistent gravity field/topographic surface simulation, upward continuation errors in the derivatives
of the Pizzetti integral to mean altitudes of about 3,000 and 1,500 m above the mean surface ranged from less than 1 mGal
(standard deviation) to less than 2 mGal (standard deviation), respectively, in the case of 2 arcmin data resolution. Least-squares
collocation performs better than this, but may require significantly greater computational resources. 相似文献
93.
Studies on small-world networks have received intensive interdisciplinary attention during the past several years. It is well-known
among researchers that a small-world network is often characterized by high connectivity and clustering, but so far there
exist few effective approaches to evaluate small-world properties, especially for spatial networks. This paper proposes a
method to examine the small-world properties of spatial networks from the perspective of network autocorrelation. Two network
autocorrelation statistics, Moran’s I and Getis–Ord’s G, are used to monitor the structural properties of networks in a process of “rewiring” networks from a regular to a random
network. We discovered that Moran’s I and Getis–Ord’s G tend to converge and have relatively low values when properties of small-world networks emerge. Three transportation networks
at the national, metropolitan, and intra-city levels are analyzed using this approach. It is found that spatial networks at
these three scales possess small-world properties when the correlation lag distances reach certain thresholds, implying that
the manifestation of small-world phenomena result from the interplay between the network structure and the dynamics taking
place on the network.
相似文献
94.
We demonstrate the possibility to improve the signal-to-noise ratio of superconducting gravity time-series by correcting for
local hydrological effects. Short-term atmospheric events associated with heavy rain induce step-like gravity signals that
deteriorate the frequency spectrum estimates. Based on 4D modeling constrained by high temporal resolution rain gauge data,
rainfall admittances for the Vienna and Membach superconducting gravity stations are calculated. This allows routine correction
for Newtonian rain water effects, which reduces the standard deviation of residuals after tidal parameter adjustment by 10%.
It also improves the correction of steps of instrumental origin when they coincide with step-like water mass signals. 相似文献
95.
J. D. Das Yazdana Shujat A. K. Saraf 《Journal of the Indian Society of Remote Sensing》2011,39(2):249-258
Employing integrated remote sensing and GIS technology the western most part of Tripura region (Northeast India) and adjoining
Bangladesh region has been investigated in the light of its geomorphological characteristics. Nature of fold ridges, several
streams and the respective drainage basins are well depicted in satellite images and digital elevation model providing meaningful
information. Quantitative parameters such as stream sinuosity, drainage basin asymmetry, basin elongation ratio have been
computed. Main rivers of the study area, namely the Gomti and Khowai follows extremely meandering path and crosses through
the transversely faulted anticlinal ridges. Fluvial anomalies viz. shift in stream channel and the abandoned meandering loops
have been inferred and mapped. The Haora river in the study area exhibits northward shift in some part. Development of drainage
system towards north and south from the drainage divide along the latitude 23°45′N indicated up arching of the region which is also corroborated by the extracted topographic profiles. It has been observed
that several tributary streams have gone dry and agricultural fields are developed along the dried up stream. These derived
parameters remained useful to understand the nature of topographical modification attributed to the possible tectonic activity. 相似文献
96.
The IVS Intensive sessions are single-baseline, 1-h VLBI sessions carried out everyday in order to determine Universal Time
(UT1). We investigate different possibilities to improve the results of such sessions. We do this investigation by extracting
2-h single-baseline sessions from the CONT08 data set. These are analysed like normal Intensives, and the results are compared
to the results of the analysis of the full CONT08 data set. We find that tropospheric asymmetry is the major error source
for the single-baseline sessions. It is possible to improve the accuracy of the estimated UT1 either by using accurate a priori
tropospheric gradients or by estimating gradients in the data analysis. 相似文献
97.
Magendran Thangavelu Sanjeevi Shanmugam Arya Kumar Bhattacharya 《Journal of the Indian Society of Remote Sensing》2011,39(4):473-483
This paper present the results of a preliminary study to assess the potential of the visible, NIR and SWIR energy of the EMR
in differentiating iron ores of different grades in a rapid manner using hyperspectral radiometry. Using different iron ore
samples from Noamundi and Joda mines, Jharkhand and Orissa, states of India, certain spectro-radiometric measurements and
geochemical analysis were carried out and the results have been presented. It was observed that the primary spectral characteristics
of these iron ores lie in the 850 to 900 nm and 650–750 nm regions. The spectral parameters for each curve used for studying
the iron ores are: (i) the slopes of the spectral curve in 685–725 nm region; (ii) position of the peak with respect to wavelength
in 730–750 nm region and (iii) radius of curvature of the absorption trough in the 850–900 nm region. Comparison of these
spectral parameters and the geochemistry of the samples indicates that the position of the peak of the curve in 730–750 nm
region shifts towards longer wavelength with increasing iron oxide content, while the slope of the curvature in the 685–725 nm
region has a strong negative correlation with the iron oxide content of the samples. Similarly, a strong negative correlation
is observed between the radius of curvature of the 850–900 nm absorption trough and the iron oxide content. Such strong correlations
indicate that hyperspectral radiometry in the visible and NIR regions can give a better estimate and quantification of the
grades of iron ores. This study has demonstrated that generation of empirical models using hyperspectral radiometric techniques
is helpful to quantify the grade of iron ores with limited geochemical analysis. 相似文献
98.
99.
Comparison of Two Data Smoothing Techniques for Vegetation Spectra Derived From EO-1 Hyperion 总被引:1,自引:0,他引:1
Anshu Miglani Shibendu S. Ray D. P. Vashishta Jai Singh Parihar 《Journal of the Indian Society of Remote Sensing》2011,39(4):443-453
Hyperspectral data are generally noisier compared to broadband multispectral data because their narrow bandwidth can only
capture very little energy that may be overcome by the self-generated noise inside the sensors. It is desirable to smoothen
the reflectance spectra. This study was carried out to see the effect of smoothing algorithms - Fast-Fourier Transform (FFT)
and Savitzky–Golay (SG) methods on the statistical properties of the vegetation spectra at varying filter sizes. The data
used in the study is the reflectance spectra data obtained from Hyperion sensor over an agriculturally dominated area in Modipuram
(Uttar Pradesh). The reflectance spectra were extracted for wheat crop at different growth stages. Filter sizes were varied
between 3 and 15 with the increment of 2. Paired t-test was carried out between the original and the smoothed data for all the filter sizes in order to see the extent of distortion
with changing filter sizes. The study showed that in FFT, beyond filter size 11, the number of locations within the spectra
where the smooth spectra were statistically different from its original counterpart increased to 14 and reaches 21 at the
filter size 15. However, in SG method, number of statistically different locations were more than those found in the FFT,
but the number of locations did not changing drastically. The number of statistically disturbed locations in SG method varied
between 16 and 19. The optimum filter size for smoothing the vegetation spectra was found to be 11 in FFT and 9 in SG method. 相似文献
100.
Evaluating the Sensitivity of Image Fusion Quality Metrics to Image Degradation in Satellite Imagery
Farhad Samadzadegan Farzaneh DadrasJavan 《Journal of the Indian Society of Remote Sensing》2011,39(4):431-441
Referring to the high potential of topographic satellite in collecting high resolution panchromatic imagery and high spectral,
multi spectral imagery, the purpose of image fusion is to produce a new image data with high spatial and spectral characteristics.
It is necessary to evaluate the quality of fused image by some quality metrics before using this product in various applications.
Up to now, several metrics have been proposed for image quality assessment; which are also applicable for quality evaluation
of fused images. However, it seems more investigations are needed to inspect the potentials of proposed Image Fusion Quality
Metrics (IFQMs) to registration accuracy, especially in high resolution satellite imagery. This paper focuses on such studies
and, using different image fusion quality metrics, experiments are conducted to evaluate the sensitivity of such metrics to
a set of high resolution satellite imagery covering urban areas. The obtained results clearly reveal that these metrics sometimes
do not behave robust in the whole area and also their obtained results are inconsistence in different patch areas in comparison
with the whole image. These limitations are in minimum situation for an image quality metric such as SAM and are completely
tangible for image quality metrics such as ERGAS in case of multi modal and DIV and CC from mono modal category. 相似文献