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901.
Geomasking sensitive health data and privacy protection: an evaluation using an E911 database 总被引:2,自引:0,他引:2
Allshouse WB Fitch MK Hampton KH Gesink DC Doherty IA Leone PA Serre ML Miller WC 《国际地球制图》2010,25(6):443-452
Geomasking is used to provide privacy protection for individual address information while maintaining spatial resolution for mapping purposes. Donut geomasking and other random perturbation geomasking algorithms rely on the assumption of a homogeneously distributed population to calculate displacement distances, leading to possible under-protection of individuals when this condition is not met. Using household data from 2007, we evaluated the performance of donut geomasking in Orange County, North Carolina. We calculated the estimated k-anonymity for every household based on the assumption of uniform household distribution. We then determined the actual k-anonymity by revealing household locations contained in the county E911 database. Census block groups in mixed-use areas with high population distribution heterogeneity were the most likely to have privacy protection below selected criteria. For heterogeneous populations, we suggest tripling the minimum displacement area in the donut to protect privacy with a less than 1% error rate. 相似文献
902.
Vitit Kantabutra J. B. “Jack” Owens Daniel P. Ames Charles N. Burns Barbara Stephenson 《Transactions in GIS》2010,14(Z1):39-58
This article introduces a type of DBMS called the Intentionally‐Linked Entities (ILE) DBMS for use as the basis for temporal and historical Geographical Information Systems. ILE represents each entity in a database only once, thereby mostly eliminating redundancy and fragmentation, two major problems in Relational and other database systems. These advantages of ILE are realized by using relationship objects and pointers to implement all of the relationships among data entities in a native fashion using dynamically‐allocated linked data structures. ILE can be considered to be a modern and extended implementation of the E/R data model. ILE also facilitates storage of things that are more faithful to the historical records, such as gazetteer entries of places with imprecisely known or unknown locations. This is difficult in Relational database systems but is a routine task using ILE because ILE is implemented using modern memory allocation techniques. We use the China Historical GIS (CHGIS) and other databases to illustrate the advantages of ILE. This is accomplished by modeling these databases in ILE and comparing them to the existing Relational implementations. 相似文献
903.
904.
The study to establish the optimum time span for distinguishing Avena ludoviciana from wheat crop based on their spectral signatures was carried out at Student’s Research Farm, Department of Agronomy during
2006–07 and 2007–08. The experimental sites during both the seasons were sandy loam in texture, with normal soil reaction
and electrical conductivity, low in organic carbon and available nitrogen and medium in available phosphorus and potassium.
The experiment was laid out in randomized block design with four replications and consisting of twelve treatments comprising
0, 10, 15, 25, 50, 75, 100, 125, 150, 200, 250 plants m−2 and a pure Avena ludoviciana plot (Tmax). The results revealed that in all the treatments irrespective of wheat and weeds, the red reflectance (%) value decreased
from 34 to 95 DAS (days after sowing) in 2006–07 and 45 DAS to 100 DAS during 2007–08, and thereafter a sharp increase was
observed in all the treatments. This trend might be due to increased chlorophyll index after 34 DAS as red reflectance was
reduced by chlorophyll absorption. Among all the treatments, Tmax (Pure Avena ludoviciana plot) had the highest red reflectance and T0 (Pure wheat plot) had a lowest value of red reflectance during both the years. The highest value of IR reflectance was obtained
at 95 DAS (2006–07) and 70 DAS (2007–08) in all the treatments. IR reflectance of wheat crop ranged between 24.61 and 61.21
per cent during 2006–07 and 27.33 and 67.3 per cent during 2007–08. However, IR reflectance values declined after 95 DAS and
70 DAS up to harvesting during 2006–07 and 2007–08. This lower reflectance may have been due to the onset of senescence. The
highest RR and NDVI values were recorded under pure wheat treatment and minimum under pure weed plots. This may be due to
dark green colour and better vigor of the wheat as compared to Avena ludoviciana. It was observed that by using RR and NDVI, pure wheat can be distinguished from pure populations of Avena ludoviciana after 34 DAS and different levels of weed populations can be discriminated amongst themselves from 68 DAS up to 107 DAS during
both the years of investigation. 相似文献
905.
Elizabeth J. Petrie Matt A. King Philip Moore David A. Lavallée 《Journal of Geodesy》2010,84(8):491-499
This study provides a first attempt at quantifying potential signal bending effects on the GPS reference frame, coordinates
and zenith tropospheric delays (ZTDs). To do this, we homogeneously reanalysed data from a global network of GPS sites spanning
14 years (1995.0–2009.0). Satellite, Earth orientation, tropospheric and ground station coordinate parameters were all estimated.
We tested the effect of geometric bending and dTEC bending corrections, which were modelled at the observation level based,
in part, on parameters from the International Reference Ionosphere 2007 model. Combined, the two bending corrections appear
to have a minimal effect on site coordinates and ZTDs except for low latitude sites. Considering five days (DOY 301–305, 28
October–1 November 2001) near ionospheric maximum in detail, they affect mean ZTDs by up to ~1.7 mm at low latitudes, reducing
to negligible levels at high latitudes. Examining the effect on coordinates in terms of power-spectra revealed the difference
to be almost entirely white noise, with noise amplitude ranging from 0.3 mm (high latitudes) to 2.4 mm (low latitudes). The
limited effect on station coordinates is probably due to the similarity in the elevation dependence of the bending term with
that of tropospheric mapping functions. The smoothed z-translation from the GPS reference frame to ITRF2005 changes by less than 2 mm, though the effect combines positively with
that from the second order ionospheric refractive index term. We conclude that, at the present time, and for most practical
purposes, the geometric and dTEC bending corrections are probably negligible at current GPS/reference frame precisions. 相似文献
906.
S. K. Goyal B. S. Chaudhary O. Singh G. K. Sethi P. K. Thakur 《Journal of the Indian Society of Remote Sensing》2010,38(2):355-364
The present study has analyzed the variability in depth to water level below ground level (bgl) vis-à-vis groundwater development
and rainfall from 1987 to 2007 in agriculture dominated Kaithal district of Haryana state in India. Spatial distribution of
groundwater depth was mapped and classified into different zones using ILWIS 3.6 GIS tools. Change detection maps were prepared
for 1987–1997 and 1997–2007. Groundwater depletion rates during successive decades were compared and critical areas with substantial
fall in groundwater levels were identified. Further, block wise trends of change in groundwater levels were also analyzed.
The water table in fresh belt areas of the district (Gulha, Pundri and Kaithal blocks) was observed to decline by a magnitude
ranging from 10 m to 23 m. In Kalayat and Rajaund blocks, the levels were found fluctuating in a relatively narrow range of
4–9 m. During 1997–2007, the depletion has been faster compared to the preceding decade. Excessive groundwater depletion in
major part of the district may be attributed to indiscriminate abstraction for irrigation and decrease in rainfall experienced
since 1998. Changes in cropping pattern and irrigation methods are needed in the study area for sustainable management of
the resource. 相似文献
907.
Integer least-squares theory for the GNSS compass 总被引:5,自引:2,他引:5
P. J. G. Teunissen 《Journal of Geodesy》2010,84(7):433-447
Global navigation satellite system (GNSS) carrier phase integer ambiguity resolution is the key to high-precision positioning
and attitude determination. In this contribution, we develop new integer least-squares (ILS) theory for the GNSS compass model,
together with efficient integer search strategies. It extends current unconstrained ILS theory to the nonlinearly constrained
case, an extension that is particularly suited for precise attitude determination. As opposed to current practice, our method
does proper justice to the a priori given information. The nonlinear baseline constraint is fully integrated into the ambiguity
objective function, thereby receiving a proper weighting in its minimization and providing guidance for the integer search.
Different search strategies are developed to compute exact and approximate solutions of the nonlinear constrained ILS problem.
Their applicability depends on the strength of the GNSS model and on the length of the baseline. Two of the presented search
strategies, a global and a local one, are based on the use of an ellipsoidal search space. This has the advantage that standard
methods can be applied. The global ellipsoidal search strategy is applicable to GNSS models of sufficient strength, while
the local ellipsoidal search strategy is applicable to models for which the baseline lengths are not too small. We also develop
search strategies for the most challenging case, namely when the curvature of the non-ellipsoidal ambiguity search space needs
to be taken into account. Two such strategies are presented, an approximate one and a rigorous, somewhat more complex, one.
The approximate one is applicable when the fixed baseline variance matrix is close to diagonal. Both methods make use of a
search and shrink strategy. The rigorous solution is efficiently obtained by means of a search and shrink strategy that uses
non-quadratic, but easy-to-evaluate, bounding functions of the ambiguity objective function. The theory presented is generally
valid and it is not restricted to any particular GNSS or combination of GNSSs. Its general applicability also applies to the
measurement scenarios (e.g. single-epoch vs. multi-epoch, or single-frequency vs. multi-frequency). In particular it is applicable
to the most challenging case of unaided, single frequency, single epoch GNSS attitude determination. The success rate performance
of the different methods is also illustrated. 相似文献
908.
Kinematic precise point positioning at remote marine platforms 总被引:6,自引:2,他引:6
Precise kinematic differential positioning using the global positioning system (GPS) at a marine platform usually requires
a relatively short distance (e.g. <500 km) to a land-based reference station. As an alternative, precise point positioning
(PPP) is normally considered free from this limiting requirement. However, due to the prerequisite of network-based satellite
products, PPP at a remote marine platform may still be affected by its distance to the reference network. Hence, this paper
investigates this scenario by configuring rings of reference stations with different radii centered on a to-be-positioned
marine platform. Particularly, we applied ambiguity resolution at a single station to PPP by estimating uncalibrated phase
delays (UPDs). We used three rings of reference stations centered on a vessel, with radii of roughly 900, 2,000 and 3,600 km,
to determine satellite clocks and UPDs independently. For comparison, we also performed differential positioning based on
a single reference station with baseline lengths of about 400, 1,700 and 2,800 km. We demonstrate that, despite the increasing
ring-network radius to a few 1,000 km, the overall change in accuracy of the satellite clocks that are used at the vessel
is smaller than 0.02 ns, and the RMS values of differences between the three sets of narrow-lane UPD estimates are around
0.05 cycles only. Moreover, the kinematic positioning accuracy of PPP is affected by the increasing ring-network radius, but
can still achieve several centimeters after ambiguity resolution when the vessel is over a few 1,000 km away from the ring
network, showing better performance than that of differential positioning. Therefore, we propose that ambiguity-fixed PPP
can be used at remote marine platforms that support precise oceanographic and geophysical applications in open oceans. 相似文献
909.
F.J. Colomer Mendoza A. Ferrer Gisbert A. Gallardo Izquierdo M.D. Bovea 《Engineering Geology》2009,105(3-4):231-238
Homogeneous earth dams that are waterproofed with geomembranes are a suitable option for storing water and other sorts of liquids, like leachates from landfills. Such dams do not require complicated engineering technical calculations, their cost is usually low and they are not difficult to construct. To ensure the geotechnical safety of the dam, the slopes of the embankment must be correctly designed and constructed. This paper provides a set of nomograms which allow the user to get the safety factor of the slopes immediately. In some cases, it is only necessary to know previously the material classification according to the Unified Soil Classifications System. From this information it can be determined whether the material is appropriate or not. If the material classification is not available, geotechnical data of the material used in the construction of the embankment are needed. Examples of the application of nomograms are presented. Secondly, the paper includes a set of equations to calculate quickly the safety factor of a slope of earth upper than 7.5 m height. 相似文献
910.
Three methods to correct for the atmospheric propagation delay in very-long-baseline interferometry (VLBI) measurements were
investigated. In the analysis, the NASA R&D experiments from January 1993 to June 1995 were used. The methods were compared
in correcting for the excess propagation delay due to water vapour, the “wet” delay, at one of the sites, the Onsala Space
Observatory on the west coast of Sweden. The three methods were: (1) estimating the wet delay using the VLBI data themselves;
(2) inferring the wet delay from water vapour radiometer (WVR) data, and (3) using independent estimates based on data from
the global positioning system (GPS). Optimum elevation cutoff angles were 22∘ and 26∘ when using WVR and GPS data, respectively. The results were found to be similar in terms of reproducibility of the estimated
baseline lengths. The shortest baselines tend to benefit from external measurements, whereas the lack of improvement in the
longer baselines may be partly due to the large amount of data thrown away when removing observations at low elevation angles.
Over a 2 week period of intensive measurements, the two methods using external data showed an overall improvement, for all
baseline lengths, compared to the first method. This indicates that there are long-term systematic errors in the wet delay
data estimated using WVR and GPS data.
Received: 27 October 1998 / Accepted: 20 May 1999 相似文献