共查询到20条相似文献，搜索用时 31 毫秒
1.
Asuncion Beamonte Pilar Gargallo Manuel Salvador 《Journal of Geographical Systems》2010,12(2):227-240
In this paper, we extend the Bayesian methodology introduced by Beamonte et al. (Stat Modelling 8:285–311, 2008) for the estimation and comparison of spatio-temporal autoregressive models (STAR) with neighbourhood effects, providing
a more general treatment that uses larger and denser nets for the number of spatial and temporal influential neighbours and
continuous distributions for their smoothing weights. This new treatment also reduces the computational time and the RAM necessities
of the estimation algorithm in Beamonte et al. (Stat Modelling 8:285–311, 2008). The procedure is illustrated by an application to the Zaragoza (Spain) real estate market, improving the goodness of fit
and the outsampling behaviour of the model thanks to a more flexible estimation of the neighbourhood parameters. 相似文献
2.
Selectivity estimation is crucial for query optimizers choosing an optimal spatial execution plan in a spatial database management system.This paper presents an Annular Bucket spatial histogram(AB histogram)that can estimate the selectivity in finer spatial selection and spatial join operations even when the spatial query has more operators or more joins.The AB histogram is represented as a set of bucket-range,bucket-count value pairs.The bucket-range often covers an annular region like a sin-gle-cell-sized photo frame.The bucket-count is the number of objects whose Minimum Bounding Rectangles(MBRs)fall between outer rectangle and inner rectangle of the bucket-range.Assuming that all MBRs in each a bucket distribute evenly,for every buck-et,we can obtain serial probabilities that satisfy a certain spatial selection or join conditions from the operations’ semantics and the spatial relations between every bucket-range and query ranges.Thus,according to some probability theories,spatial selection or join selectivity can be estimated by the every bucket-count and its probabilities.This paper also shows a way to generate an updated AB histogram from an original AB histogram and those probabilities.Our tests show that the AB histogram not only supports the selectivity estimation of spatial selection or spatial join with "disjoint","intersect","within","contains",and "overlap" operators but also provides an approach to generate a reliable updated histogram whose spatial distribution is close to the distribution of ac-tual query result. 相似文献
3.
One of the most basic and important tools in optimal spectral gravity field modelling is the method of Wiener filtering.
Originally developed for applications in analogue signal analysis and communication engineering, Wiener filtering has become
a standard linear estimation technique of modern operational geodesy, either as an independent practical tool for data de-noising
in the frequency domain or as an integral component of a more general signal estimation methodology (input–output systems
theory). Its theoretical framework is based on the Wiener–Kolmogorov linear prediction theory for stationary random fields
in the presence of additive external noise, and thus it is closely related to the (more familiar to geodesists) method of
least-squares collocation with random observation errors. The main drawback of Wiener filtering that makes its use in many
geodetic applications problematic stems from the stationarity assumption for both the signal and the noise involved in the
approximation problem. A modified Wiener-type linear estimation filter is introduced that can be used with noisy data obtained
from an arbitrary deterministic field under the masking of non-stationary random observation errors. In addition, the sampling
resolution of the input data is explicitly taken into account within the estimation algorithm, resulting in a resolution-dependent
optimal noise filter. This provides a more insightful approach to spectral filtering techniques for noise reduction, since
the data resolution parameter has not been directly incorporated in previous formulations of frequency-domain estimation problems
for gravity field signals with discrete noisy data.
Received: 1 November 2000 / Accepted: 19 June 2001 相似文献
4.
A. V. Suresh Babu V. Venkateshwar Rao I. V. Muralikrishna 《Journal of the Indian Society of Remote Sensing》2007,35(1):81-91
Water Utilisation Index (WUI) defined as area irrigated per unit volume is a measure of water delivery performance and constitutes
one of the important spatial performance indicators of an irrigation system. WUI also forms basis for evaluating the adequacy
of seasonal irrigation supplies in an irrigation system (inverse of WUI is delta, i.e. depth of water supplied to a given
irrigation unit). In the present study WUI and adequacy indicators were used in benchmarking the performance of Nagarjunasagar
Left Canal Command (NSLC) in Andhra Pradesh. Optimised temporal satellite data of rabi season during the years 1990–91 and
1998–99 was used in deriving irrigated crop areas adopting hierarchical classification approach. Paddy is the predominant
crop grown and cotton, chillies, sugarcane etc. are the other crops grown in the study area. Equivalent wet area (paddy crop
area) was estimated using the operationally used project specific conversion factors. WUI was estimated at disaggregated level
viz., distributary, irrigation block, irrigation zone level using the canal discharge data. At project level, WUI estimated
to be 65 ha/MCM and 92 ha/MCM during rabi season of 1990–91 and 1998–99 years respectively. A comparison of total irrigated
area and discharges corresponding to both the years indicate that irrigation service is extensive and sub optimal during 1998–99
and it is intensive and optimal in 1990–91. It was also observed that WUI is lesser in blocks of with higher Culturable Command
Area (CCA) compared to the blocks of lower CCA. All the disaggregated units were ranked into various groups of different levels
of water distribution performance. The study demonstrates the utility of WUI as spatial performance indicator and thus useful
for benchmarking studies of irrigation command areas. The WUI together with satellite data derived spatial irrigation intensity,
crop productivity constitutes important benchmarking indices in irrigation command areas. 相似文献
5.
C. Jeganathan V. K. Dadhwal Kiran Gupta P. L. N. Raju 《Journal of the Indian Society of Remote Sensing》2009,37(4):539-549
The study compared forest cover maps derived using coarse resolution vegetation continuous fields (MODIS VCF; 500m resolution)
with the maps derived from medium resolution (24m; IRS LISS-III) data. The comparison of VCF, per cent tree cover product,
for the years 2000 to 2004 with LISS III forest density class maps of 2001 and 2003 was carried out for two sites representing
hilly (Uttarakhand) and undulating terrains (Madhya Pradesh). Slicing VCF to corresponding forest crown cover, i.e., 0–10%,
10–40%, 40–70% and >70% produced considerable difference in forest area estimates when compared to original LISS III derived
crown cover area. The corresponding value range in VCF for 0–10% of actual forest cover were 0–31% and 0–25% in 2 sites respectively,
and the respective limit was consistent at 1–20% when VCF range were sliced with respect to upscaled LISS III at 500m resolution.
Similarly, all other class limits were also found through iterative process. These limits were similar, within a site, across
five years. Spatial Kappa match between these two data indicated higher match in 40–70% class, and also in undulating site.
When compared at same resolution, similar forest area cover estimated with weighted area upscaling gave closest match. The
study is useful in knowing the usability and limits of VCF product, and utility of spatial Kappa. 相似文献
6.
Hierarchical spatial interaction among the Italian regions: a nonlinear relative dynamics approach 总被引：2，自引：2，他引：0
Regional interactions and spillover effects should be considered as important factors in growth analysis of regional economies.
Using modified versions of the Dendrinos–Sonis model, this paper analyses the spatial hierarchical system of Italy. The interaction
among Italian regions is considered at three different levels of spatial aggregation, the NUTS-1, NUTS-2 and NUTS-3 levels.
Compared to more popular spatial econometric approaches, the Dendrinos–Sonis model and its extensions provide greater flexibility
in the way interaction between regions is handled but the results strongly depend on the choice of a reference region.
相似文献
| Geoffrey J. D. HewingsEmail: |
7.
Burkhard Schaffrin 《Journal of Geodesy》2008,82(2):113-121
In a linear Gauss–Markov model, the parameter estimates from BLUUE (Best Linear Uniformly Unbiased Estimate) are not robust
against possible outliers in the observations. Moreover, by giving up the unbiasedness constraint, the mean squared error
(MSE) risk may be further reduced, in particular when the problem is ill-posed. In this paper, the α-weighted S-homBLE (Best homogeneously Linear Estimate) is derived via formulas originally used for variance component estimation on
the basis of the repro-BIQUUE (reproducing Best Invariant Quadratic Uniformly Unbiased Estimate) principle in a model with
stochastic prior information. In the present model, however, such prior information is not included, which allows the comparison
of the stochastic approach (α-weighted S-homBLE) with the well-established algebraic approach of Tykhonov–Phillips regularization, also known as R-HAPS (Hybrid APproximation Solution), whenever the inverse of the “substitute matrix” S exists and is chosen as the R matrix that defines the relative impact of the regularizing term on the final result.
The delay in publishing this paper is due to a number of unfortunate complications. It was first submitted as a multi-author
paper in two parts. Due to some miscommunication among the original authors, it was reassigned to one of the J Geod special
issues, but later reassigned at this author’s request to a standard issue of J Geod. This compounded with a difficulty to
find willing reviewers to slow the process. We apologize to the author. 相似文献
8.
From fields to objects: A review of geographic boundary analysis 总被引：12，自引：0，他引：12
Geographic boundary analysis is a relatively new approach unfamiliar to many spatial analysts. It is best viewed as a technique
for defining objects – geographic boundaries – on spatial fields, and for evaluating the statistical significance of characteristics
of those boundary objects. This is accomplished using null spatial models representative of the spatial processes expected
in the absence of boundary-generating phenomena. Close ties to the object-field dialectic eminently suit boundary analysis
to GIS data. The majority of existing spatial methods are field-based in that they describe, estimate, or predict how attributes
(variables defining the field) vary through geographic space. Such methods are appropriate for field representations but not
object representations. As the object-field paradigm gains currency in geographic information science, appropriate techniques
for the statistical analysis of objects are required. The methods reviewed in this paper are a promising foundation. Geographic
boundary analysis is clearly a valuable addition to the spatial statistical toolbox.? This paper presents the philosophy of,
and motivations for geographic boundary analysis. It defines commonly used statistics for quantifying boundaries and their
characteristics, as well as simulation procedures for evaluating their significance. We review applications of these techniques,
with the objective of making this promising approach accessible to the GIS-spatial analysis community. We also describe the
implementation of these methods within geographic boundary analysis software: GEM.
Received: 22 March 1999 / Accepted: 7 September 1999 相似文献
9.
Summary . It is well known that for the comparison and combination of geodetic networks their heterogeneous datum definitions are
well to be considered. Various algorithms have been developed for this purpose. As an alternative concept to deal with hybrid
datum problems, the operator parallel sum of matrices is introduced in this paper. To begin with, a definition is given and some basic properties are explained. To demonstrate
the usefulness of the operator, two practical applications are given. The first deals with the estimation of parameters describing
the deformation of two networks which are to be compared to each other. The second one treats the estimation of parameters
representing the heterogeneous datum definitions of two networks which are to be merged into a hybrid network. It will be
shown that – regardless of the datum definitions of the preadjusted individual networks – the parallel sum of matrices can
be used to simplify the algorithms applied for the estimation of those parameters.
Received 15 December 1995; Accepted 24 September 1996 相似文献
10.
J. Grodecki 《Journal of Geodesy》2001,75(2-3):157-163
A new estimator of variance–covariance components is presented. The proposed estimator is derived by applying the principle
of maximum-likelihood estimation to the posterior probability density function for the case when no prior information is available.
Received: 9 August 1999 / Accepted: 10 November 2000 相似文献
11.
Estimation and validation of snow surface temperature using modis data for snow-avalanche studies in NW-Himalaya 总被引：1，自引：0，他引：1
H. S. Negi N. K. Thakur V. D. Mishra 《Journal of the Indian Society of Remote Sensing》2007,35(4):287-299
Snow avalanche studies require different snow-meteorological parameters for avalanche forecasting. Snow surface temperature
is one of the major parameters, which is responsible for the evolution of snow pack characteristics. In the present paper,
the snow surface temperature was estimated using TERRA satellite based — Moderate resolution imaging spectroradiometer (MODIS)
sensor for NW-Himalayas. Ground data observed by automatic weather stations (AWS) was used to calibrate the brightness temperature
obtained by MODIS thermal bands data into the actual snow surface temperature data through regression analysis. A split window
technique has been implemented for the estimation of snow surface temperature. The multi-date satellite derived snow surface
temperature was validated with ground data of winter 2004–05 and 2005–06 collected at various observation stations located
in different ranges of NW-Himalaya. Good correlations were observed for Upper Himalaya (0.98, 0.98), Middle Himalaya (0.92,
0.96) and Lower Himalaya (0.88, 0.82) for 2004–05 and 2005–06 winter respectively. Further, estimated snow surface temperature
was also verified with snow-cover information collected by manned observatories and area delineated by thematic maps of snow
surface temperature was validated with the different snow climatic zones of NW-Himalaya. 相似文献
12.
This paper presents a continuous version of the model of distribution dynamics to analyse the transition dynamics and implied
long-run behaviour of the EU-27 NUTS-2 regions over the period 1995–2003. It departs from previous research in two respects:
first, by introducing kernel estimation and three-dimensional stacked conditional density plots as well as highest density regions
plots for the visualisation of the transition function, based on Hyndman et al. (J Comput Graph Stat 5(4):315–336, 1996), and second, by combining Getis’ spatial filtering view with kernel estimation to explicitly account for the spatial dimension of the
growth process. The results of the analysis indicate a very slow catching-up of the poorest regions with the richer ones,
a process of shifting away of a small group of very rich regions, and highlight the importance of geography in understanding
regional income distribution dynamics.
相似文献
| Manfred M. FischerEmail: |
13.
A new estimator for VLBI baseline length repeatability 总被引：1，自引：1，他引：0
O. Titov 《Journal of Geodesy》2009,83(11):1041-1049
The goal of this paper is to introduce a more effective technique to approximate for the “repeatability–baseline length” relationship
that is used to evaluate the quality of geodetic VLBI results. Traditionally, this relationship is approximated by a quadratic
function of baseline length over all baselines. The new model incorporates the mean number of observed group delays of the
reference radio sources (i.e. estimated as global parameters) used in the estimation of each baseline. It is shown that the
new method provides a better approximation of the “repeatability–baseline length” relationship than the traditional model.
Further development of the new approach comes down to modeling the repeatability as a function of two parameters: baseline
length and baseline slewing rate. Within the framework of this new approach the station vertical and horizontal uncertainties
can be treated as a function of baseline length. While the previous relationship indicated that the station vertical uncertainties
are generally 4–5 times larger than the horizontal uncertainties, the vertical uncertainties as determined by the new method
are only larger by a factor of 1.44 over all baseline lengths. 相似文献
14.
The global positioning system (GPS) model is distinctive in the way that the unknown parameters are not only real-valued,
the baseline coordinates, but also integers, the phase ambiguities. The GPS model therefore leads to a mixed integer–real-valued
estimation problem. Common solutions are the float solution, which ignores the ambiguities being integers, or the fixed solution,
where the ambiguities are estimated as integers and then are fixed. Confidence regions, so-called HPD (highest posterior density)
regions, for the GPS baselines are derived by Bayesian statistics. They take care of the integer character of the phase ambiguities
but still consider them as unknown parameters. Estimating these confidence regions leads to a numerical integration problem
which is solved by Monte Carlo methods. This is computationally expensive so that approximations of the confidence regions
are also developed. In an example it is shown that for a high confidence level the confidence region consists of more than
one region.
Received: 1 February 2001 / Accepted: 18 July 2001 相似文献
15.
In the linear estimation problem associated with an experiment that is exactly repeated a number of times, the estimation
parameters may naturally be partitioned into two groups, those that are common to all repetitions, and those that are particular
to each repeat experiment. We derive least-squares solutions that minimise in norm either group of parameters, as also the
trace of the corresponding covariance matrix. These solutions are applied to the station adjustment of triangulation surveying,
and to the estimation problem of satellite radar altimetry: to estimate simultaneously mean sea surface heights and residual
radial orbit errors, while minimising the norm of either group of parameters. This altimetry problem is considered in the
cases of collinear, local crossover and global crossover data.
Received: 6 January 1997 / Accepted: 21 December 1998 相似文献
16.
Adaptive Kalman Filtering for INS/GPS 总被引：69，自引：0，他引：69
After reviewing the two main approaches of adaptive Kalman filtering, namely, innovation-based adaptive estimation (IAE)
and multiple-model-based adaptive estimation (MMAE), the detailed development of an innovation-based adaptive Kalman filter
for an integrated inertial navigation system/global positioning system (INS/GPS) is given. The developed adaptive Kalman filter
is based on the maximum likelihood criterion for the proper choice of the filter weight and hence the filter gain factors.
Results from two kinematic field tests in which the INS/GPS was compared to highly precise reference data are presented. Results
show that the adaptive Kalman filter outperforms the conventional Kalman filter by tuning either the system noise variance–covariance
(V–C) matrix `Q' or the update measurement noise V–C matrix `R' or both of them.
Received: 14 September 1998 / Accepted: 21 December 1998 相似文献
17.
Colin Robertson Trisalyn A. Nelson Barry Boots Michael A. Wulder 《Journal of Geographical Systems》2007,9(3):207-227
Research questions regarding temporal change in spatial patterns are increasingly common in geographical analysis. In this
research, we explore and extend an approach to the spatial–temporal analysis of polygons that are spatially distinct and experience
discrete changes though time. We present five new movement events for describing spatial processes: displacement, convergence,
divergence, fragmentation and concentration. Spatial–temporal measures of events for size and direction are presented for
two time periods, and multiple time periods. Size change metrics are based on area overlaps and a modified cone-based model
is used for calculating polygon directional relationships. Quantitative directional measures are used to develop application
specific metrics, such as an estimation of the concentration parameter for a von Mises distribution, and the directional rate
of spread. The utility of the STAMP methods are demonstrated by a case study on the spread of a wildfire in northwestern Montana.
相似文献
18.
The problem of the convergence of the collocation solution to the true gravity field was defined long ago (Tscherning in Boll
Geod Sci Affini 39:221–252, 1978) and some results were derived, in particular by Krarup (Boll Geod Sci Affini 40:225–240,
1981). The problem is taken up again in the context of the stochastic interpretation of collocation theory and some new results
are derived, showing that, when the potential T can be really continued down to a Bjerhammar sphere, we have a quite general convergence property in the noiseless case.
When noise is present in data, still reasonable convergence results hold true.
“Democrito che ’l mondo a caso pone” “Democritus who made the world stochastic” Dante Alighieri, La Divina Commedia, Inferno, IV – 136 相似文献
19.
V. S. Schwarze 《Journal of Geodesy》1999,73(11):594-602
The reformulation of geodetic measurement processes within the framework of general relativity is discussed. The metric tensor
plays an important role in general relativity and has to be represented with respect to a set of appropriate charts. Almost
every quantity of interest in geodetic or geophysical applications refers to a geocentric, Earth-fixed coordinate system (chart),
therefore they are of great importance in geodesy and geophysics. The space–time metric with respect to an Earth-fixed chart
is derived at first post-Newtonian order. The field equations determining the terrestrial gravitational field are derived
and its explicit representation is outlined. The impact of the results on the modelling of geodetic measurement processes
including space–time positioning scenarios as well as the high-precision gravitational field estimation is outlined.
Received: 7 January 1998 / Accepted: 17 August 1999 相似文献
20.
Spatial statistical techniques for aggregating point objects extracted from high spatial resolution remotely sensed imagery 总被引：3，自引：0，他引：3
Trisalyn Nelson K. Olaf Niemann Michael A. Wulder 《Journal of Geographical Systems》2002,4(4):423-433
Using a local maximum filter, individual trees were extracted from a 1 m spatial resolution IKONOS image and represented
as points. The spatial pattern of individual trees was determined to represent forest age (a surrogate for forest structure).
Point attributes, based on the spatial pattern of trees, were generated via nearest neighbour statistics and used as the basis
for aggregating points into forest structure units. The forest structure units allowed for the mapping of a forested area
into one of three age categories: young (1–20 years), intermediate (21–120 years), and mature (>120 years). This research
indicates a new approach to image processing, where objects generated from the processing of image data (rather than pixels
or spectral values) are subjected to spatial statistical analysis to estimate an attribute relating an aspect of forest structure.
Received: 22 April 2002 / Accepted: 23 November 2002 相似文献