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401.
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
402.
Multipath error is considered one of the major errors affecting GPS observations. One can benefit from the repetition of satellite
geometry approximately every sidereal day, and apply filtering to help minimize this error. For GPS data at 1 s interval processed
using a double-difference strategy, using the day-to-day coordinate or carrier-phase residual autocorrelation determined with
a 10-h window leads to the steadiest estimates of the error-repeat lag, although a window as short as 2 h can produce an acceptable
value with > 97% of the optimal lag’s correlation. We conclude that although the lag may vary with time, such variation is
marginal and there is little advantage in using a satellite-specific or other time-varying lag in double-difference processing.
We filter the GPS data either by stacking a number of days of processed coordinate residuals using the optimum “sidereal”
lag (23 h 55 m 54 s), and removing these stacked residuals from the day in question (coordinate space), or by a similar method
using double-difference carrier-phase residuals (observational space). Either method results in more consistent and homogeneous
set of coordinates throughout the dataset compared with unfiltered processing. Coordinate stacking reduces geometry-related
repeating errors (mainly multipath) better than carrier-phase residual stacking, although the latter takes less processing
time to achieve final filtered coordinates. Thus, the optimal stacking method will depend on whether coordinate precision
or computational time is the over-riding criterion. 相似文献
403.
An Improved Hilbert Curve for Parallel Spatial Data Partitioning 总被引:1,自引:0,他引:1
MENG Lingkui HUANG Changqing ZHAO Chunyu LIN Zhiyong 《地球空间信息科学学报》2007,10(4):282-286
A novel Hilbert-curve is introduced for parallel spatial data partitioning, with consideration of the huge-amount property of spatial information and the variable-length characteristic of vector data i... 相似文献
404.
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
405.
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
406.
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
407.
408.
Sheshakumar K. Goroshi R. P. Singh S. Panigrahy J. S. Parihar 《Journal of the Indian Society of Remote Sensing》2011,39(3):315-321
This paper highlights the spatial and temporal variability of atmospheric columnar methane (CH4) concentration over India and its correlation with the terrestrial vegetation dynamics. SCanning IMaging Absorption spectrometer
for Atmospheric CHartographY (SCIAMACHY) on board ENVIronmental SATellite (ENVISAT) data product (0.5° × 0.5°) was used to
analyze the atmospheric CH4 concentration. Satellite Pour l'Observation de la Terre (SPOT)-VEGETATION sensor’s Normalized Difference Vegetation Index
(NDVI) product, aggregated at 0.5° × 0.5° grid level for the same period (2004 and 2005), was used to correlate the with CH4 concentration. Analysis showed mean monthly CH4 concentration during the Kharif season varied from 1,704 parts per billion volume (ppbv) to 1,780 ppbv with the lowest value in May and the highest value
in September. Correspondingly, mean NDVI varied from 0.28 (May) to 0.53 (September). Analysis of correlation between CH4 concentration and NDVI values over India showed positive correlation (r = 0.76; n = 6) in Kharif season. Further analysis using land cover information showed characteristic low correlation in natural vegetation region
and high correlation in agricultural area. Grids, particularly falling in the Indo-Gangetic Plains showed positive correlation.
This could be attributed to the rice crop which is grown as a predominant crop during this period. The CH4 concentration pattern matched well with growth pattern of rice with the highest concentration coinciding with the peak growth
period of crop in the September. Characteristically low correlation was observed (r = 0.1; n = 6) in deserts of Rajasthan and forested Himalayan ecosystem. Thus, the paper emphasizes the synergistic use of different
satellite based data in understanding the variability of atmospheric CH4 concentration in relation to vegetation. 相似文献
409.
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
410.
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