Determination of rasterizing error a case study with the soil map of The Netherlands

Abstract

The digital soil map of The Netherlands (scale 1: 50 000) in vector form was rasterized using three sizes of raster cell and two different rasterizing methods. The rasterizing errors were estimated for several map sheets of different complexity using the double-conversion method, the Switzer method and the Goodchild method. The relationship between the complexity of the maps, indicated by the boundary index, and the rasterizing error is presented as a regression equation. The double-conversion method provided a better estimation of the rasterizing error than the other two methods. Differences of less than 1 per cent were found between the rasterizing methods used.     

嫦娥一号月球地形模型的一些应用研究

利用嫦娥一号绕月卫星激光高度计数据获取得到的新的360 阶次的地形模型CLTMs03,开展了初步应用研究,包括对嫦娥一号CCD立体相机数据进行了校对,发现并了解立体相机分析中的约900 m的垂向系统误差;利用撞击坑计数法,基于标校后的照相数据对嫦娥一号地形中新发现的玉兔火山区域的年龄特征进行了分析;结合新的CLTM-s03 地形模型和CEGM-02 重力场模型,新证实了西拉德撞击坑是一个布格质量瘤异常区域。     

Sensitivity and inversion of borehole flexural dispersions for formation parameters

Propagation characteristics of borehole flexural waves are functions of five borehole, fluid and formation parameters. Uncertainties in any of these model parameters may introduce errors in the estimate of formation shear-wave speed. Other sources of error in the estimate may be caused by deviations from the assumed circular borehole cross-section or heterogeneity in the material properties of formation in the vicinity of a borehole from the usually assumed homogeneous properties. The influence of uncertainties in model parameters on borehole flexural dispersion has been calculated from a general perturbation model based on Hamilton's principle. A sensitivity analysis of the flexural dispersion to small variations in the model parameters shows that the formation shear speed has by far the most dominant influence in a slow formation. In contrast, the flexural dispersion in a fast formation is significantly influenced by three of the five model parameters: the formation shear speed, the borehole fluid compressional speed and the borehole diameter. The frequency dependence of these sensitivity functions indicates that the inversion of flexural dispersion for formation shear speed is optimal in the range 2–4 kHz for a borehole of diameter 25.4 cm. The range of validity of the perturbation model has been estimated by comparing results of concentric annuli of different thicknesses, and shear-wave speeds different from that of the formation with those from exact numerical solutions from a modal search program. Generally, the perturbation results for altered annuli of thicknesses up to 15 cm are accurate to within 1 per cent for a shear-wave speed 10 per cent lower than that of the formation. This difference between the perturbation and exact results increases to approximately 1 to 3 per cent for a shear-wave speed 20 per cent lower than that of the formation.     

Magnetic fabric and its significance in the Florianópolis dyke swarm, southern Brazil

Magnetic fabric was determined by applying the anisotropy from the low-field magnetic susceptibility (AMS) technique in 62 mafic dykes from the Mesozoic Florianópolis (Santa Catarina Island) dyke swarm, southern Brazil. These dykes cut the crystalline basement rocks, which are mainly Proterozoic. They are vertical or subvertical in dip and trend mainly NE, although NW-trending dykes are also found. Dykes are tholeiitic in composition and are geochemically similar to those from the Ponta Grossa swarm. Thicknesses vary from 0.3 to 60 m. Polished sections show that titanomagnetites carry the AMS in these dykes. Hysteresis parameters show that the magnetic minerals fall in the PSD range. Two types of magnetic fabric are recognized. Type I is characterized by K ₁- K ₂ parallel to the dyke wall, representing magma flow within the dykes; type II, with K ₁- K ₃ parallel to the dyke wall, was found in four dykes. Type I is found in 94 per cent of the dykes, and approximately 20 per cent of these have K ₁ inclinations of less than 30°, suggesting horizontal or subhorizontal flow. About 80 per cent have K ₁ inclinations of greater than 30°, due to inclined to vertical flow. The comparison of AMS studies from both the Florianópolis and the Ponta Grossa dykes suggests a source position closer to Santa Catarina Island than the Ponta Grossa arch.     

THE INFLUENCE OF TEMPERATURE GRADIENT AND VARIATION OF COMPOSITION IN THE MANTLE ON THE COMPUTATION OF DENSITY VALUES IN EARTH MODEL A

i
The effect of errors in the expression for dp/dr used in constructing the Earth Model A is examined. It is shown that, for a 10 per cent error in dp/dr arising from possible deviations from adiabatic gradients and uniform chemical composition in the regions B and D, the maximum error in the density ρ in the mantle of Model A would be only 0.07 g/cm³. This is less than one-quarter of the error that would be entailed if a 10 per cent correction to dp/dr were applied throughout the mantle. Thus temperature deviations to any likely extent cannot be considered as serious sources of error in the density distribution of Model A.     

The Backus–Gilbert approach to the three-dimensional structure in the upper mantle – I. Lateral variation of surface wave phase velocity with its error and resolution

Summary. The Backus–Gilbert method is applied to obtain the phase velocity variations on a sphere from the measured phase velocity. Narrow peak kernels, with radii of about 2000 km, are obtained for almost everywhere on the sphere. The phase velocity results are thus interpreted as an average within such regions. The most trouble comes from the antipodal peak in the resolution kernel. This is evaluated as contamination and is incorporated in the error estimation. The total error, which is a root mean square of contamination from the antipodal peak and statistical error estimated from the data covariance matrix, is about 1 per cent of the phase velocity in the average earth model, which is the Preliminary Reference Earth Model (PREM). However, there is about a factor of 2 variation of errors on the sphere. Maximum variations of phase velocity are about 3–4 per cent of the phase velocity in the average earth model, and thus there still remain anomalies which exceed estimated errors. The estimated errors correspond to one standard deviation under the assumptions of uncorrelated Gaussian distribution. For high confidence interval, they show that statistically significant anomalies are scarce for the current data set. Generally, Love-wave phase velocity maps show more resolved features than Rayleigh-wave maps and we can see, in high confidence maps, fast velocities in old oceans and old continents and slow velocities in tectonically active regions like the East Pacific Rise and various back-arc regions.     

CONDITION NUMBERS, ITERATIVE REFINEMENT AND ERROR BOUNDS

Concentration estimates of components present in a sample mixture can be obtained using matrixmathematics. In the past, the condition number of the calibration matrix has been used to give anamplification factor by which uncertainties in data can work through to errors in the concentrationestimates. This paper explores an additional interpretation of condition numbers with regards tosignificant figures and rounding errors. A procedure is suggested which will always give the most accurateconcentration estimates provided the calibration matrix is not too ill-conditioned. Condition numbershave also been used by analytical chemists to discuss the error bounds for concentration estimates.Unfortunately, only one representative error bound can be approximated for all the components. Thispaper will show how to compute bounds for individual concentration estimates obtained as solutions to asystem of m equations and n unknowns. The procedure is appropriate when calibration data and sampleresponses are inaccurate.     

The determination of resistivity and porosity of the sediment and fractured basalt layers near the Juan de Fuca Ridge

Summary. In the summer of 1984 an electrical survey using magnetometric off-shore electrical sounding (MOSES) was conducted at two sites in Middle Valley, part of the northern Juan de Fuca Ridge complex. MOSES has been designed to minimize the difficulties inherent in electrical surveys of the crust below the electrically conductive sea layer. Site 1, at 48°32N, 128°42W, is in the central part of the turbidite-filled basin. Using a two-layer model of conductive sediments overlying a fractured basalt basement, the sediment resistivity and thickness were found to be 0.82 ± 0.06 Ωm and 1800 ± 300 m, respectively. The basement resistivity, although not well constrained by the data is consistent with the results obtained at site 2.
Site 2, located at 48°10N, 128°50W, has a thinner sediment layer, which appears to vary with position. The sediment conductivity—thickness product is the parameter determined by the data. If the sediment resistivity were the same as at site 1, the sediment thickness would be 140 ± 30 m to the SE of site 2, and 240 ± 55 m to the NW. The fractured basalt basement has a resistivity of 8.5 ± 3.4 Ωm and is at least 1000 m thick.
Using temperature-corrected pore fluid resistivity, the calculated porosity is found to vary from 62 per cent at the top to 21 per cent at the base of the sediments and is 8 per cent in the basement. These values are in good agreement with estimates from seismic velocities for a thick turbidite sequence in a nearby sediment-filled basin and determined for layer 2A/B basalts in DSDP hole 504B, respectively.     

Permo-Carboniferous (Kiaman) palaeointensity results from the western Bohemian Massif, Germany

Thellier palaeointensity analyses were carried out on samples from three quartz porphyry intrusions located within the western part of the Bohemian Massif close to the German-Czech Republic border. These intrusives have been dated at 280-275 Ma. which places them in the main part of the Permo-Carboniferous (Kiaman) Reversed Superchron (P-CRS). This age is consistent with the mean characteristic remanence direction calculated at D/ I = 204/- 1, giving a VGP at 36N, 341E. Palaeointensity values range from 6.6 μT to 22.1 μT, with a mean value of 12.0 ± 1.3 μT, which has a corresponding VDM value of (3.0 ± 1.2) × 10²² A m². This suggests that the geomagnetic field strength recorded by the quartz porphyries is only 37 per cent of the current value, supporting recent studies that report a field strength of between 25 and 40 per cent of the present-day value during the P-CRS.     

Flood Fatalities in Australia, 1788-1996

Information on fatalities from flooding in Australia has been compiled from newspapers, historical accounts, and government and scientific reports. Records covering 1788 to 1996 indicate that at least 2213 persons have been killed in floods in Australia. The overall decadal death rate has decreased from 23.98 per 100 000 population in the 1800s to 0.04 per 100 000 in the 1990s. The greatest number of fatalities has occurred in New South Wales but, taking population into account, Queensland has been the most vulnerable state historically as, more recently, has been the Northern Territory. Most fatalities have occurred during February, and amongst males (80.6 per cent). The overall male:female death and death-rate ratios are both 4:1. Whereas the male:female death-rate ratio has fluctuated over time from 10:1 to 1:1, it does not approach equality. Most fatalities (38.5 per cent) have occurred through attempts to cross creeks, bridges or roads in times of flood. Another 31.5 per cent of victims were in houses-the majority awaiting rescue, or simply unaware of the flood. Of the total known deaths, work-related fatalities have accounted for 12.4 per cent, and recreational pursuits for 5.7 per cent.     

Creating and coupling a high-resolution DTM with a 1-D hydraulic model in a GIS for scenario-based assessment of avulsion hazard in a gravel-bed river

In this paper we explore the development and assimilation of a high resolution topographic surface with a one-dimensional hydraulic model for investigation of avulsion hazard potential on a gravel-bed river. A detailed channel and floodplain digital terrain model (DTM) is created to define the geometry parameter required by the 1D hydraulic model HEC-RAS. The ability to extract dense and optimally located cross-sections is presented as a means to optimize HEC-RAS performance. A number of flood scenarios are then run in HEC-RAS to determine the inundation potential of modeled events, the post-processed output of which facilitates calculation of spatially explicit shear stress (τ) and level of geomorphic work (specific stream power per unit bed area, ω) for each of these. Further enhancing this scenario-based approach, the DTM is modified to simulate a large woody debris (LWD) jam and active-channel sediment aggradation to assess impact on innundation, τ, and ω, under previously modeled flow conditions. The high resolution DTM facilitates overlay and evaluation of modeled scenario results in a spatially explicit context containing considerable detail of hydrogeomorphic and other features influencing hydraulics (bars, secondary and scour channels, levees). This offers advantages for: (i) assessing the avulsion hazard potential and spatial distribution of other hydrologic and fluvial geomorphic processes; and (ii) exploration of the potential impacts of specific management strategies on the channel, including river restoration activities.     

矢量和栅格数据土地利用结构分维值比较——以苏州为例

分形理论对处理土地利用结构之类的非线性对象具有较强实用价值, 分维值作为该理论的重要测度指标, 其计算常基于栅格数据, 由此导致了土地结构边界信息的损失, 也减弱了分维值对土地利用空间结构特性的揭示作用。本文以苏州市1:10 万土地利用数据为例, 对研究区的土地利用空间格局进行分形分析, 通过分析不同栅格大小的土地利用分维值, 建立分维值与栅格粒度之间的定量关系, 并通过栅格数据推算矢量分维值, 分析推算误差及其原因。结果表明, 苏州市土地利用格局符合分形理论的一般规律;苏州市整体土地利用程度较高, 耕地、建设用地结构较为简单, 而未利用地、林草地结构较复杂, 水域斑块结构复杂性较低;随着栅格粒度的增加, 土地利用分维值呈现增加趋势, 且粒度与分维值之间存在二次函数的定量关系, 可以通过此关系式在一定误差范围内推求矢量数据的土地结构分维值, 斑块数量与整体规模是影响推求精度的重要原因。     

Modelling soil map-unit inclusions by Monte Carlo simulation

Abstract

Error and uncertainty in spatial databases have gained considerable attention in recent years. The concern is that, as in other computer applications and, indeed, all analyses, poor quality input data will yield even worse output. Various methods for analysis of uncertainty have been developed, but none has been shown to be directly applicable to an actual geographical information system application in the area of natural resources. In spatial data on natural resources in general, and in soils data in particular, a major cause of error is the inclusion of unmapped units within areas delineated on the map as uniform. In this paper, two alternative algorithms for simulating inclusions in categorical natural resource maps are detailed. Their usefulness is shown by a simplified Monte Carlo testing to evaluate the accuracy of agricultural land valuation using land use and the soil information. Using two test areas it is possible to show that errors of as much as 6 per cent may result in the process of land valuation, with simulated valuations both above and below the actual values. Thus, although an actual monetary cost of the error term is estimated here, it is not found to be large.     

A magnetic investigation of a Late Quaternary loess/palaeosol record in Siberia

A Late Quaternary loess/palaeosol sequence at Kurtak in the Yenisey River valley, southern Siberia, has been studied magnetically. The 34  m section (340 samples) exhibits variations in magnetic susceptibility which can be correlated with oxygen isotope stages 1–7. A detailed sampling of stage 5 (a further 209 samples) permits the identification of substages 5a–e. The susceptibility variations themselves are in the opposite sense to that found in the classic sections of the Chinese Loess Plateau, but are in agreement with the 'wind-intensity' model which has been put forward to explain similar findings in loess sequences in Alaska. Published results for the susceptibility of magnetite imply volume fractions of ≈0.2 per cent in glacial stages 2 and 4, dropping to ≈0.05 per cent in stages 1, 3 and 5. These fluctuations match the aeolian flux variations observed in core V21–146 from the north Pacific. Even though the warmer intervals are characterized by lower susceptibilities, the observed frequency dependence of susceptibility indicates that new magnetic material is produced as a result of pedogenesis during interglacial and interstadial times.     

Combining airborne and terrestrial laser scanning for quantifying erosion and deposition by a debris flow event

We quantified the sediment volume transported by a major debris flow event in the Halltal, Austrian Alps, using a combination of terrestrial (TLS) and airborne laser scanning (ALS) which has rarely been carried out before. A digital terrain model (DTM) derived from ALS data (pre-event surface) was combined with a DTM derived from TLS data (post-event surface). Both datasets were aligned and compared in a cut and fill analysis estimating differential volumes.The main focus lay on the evaluation and accuracy assessment of the applied method. Tie-point based registration of both datasets proved to be insufficient; additional alignment by Multi Station Adjustment was necessary to minimise the averaged height error between both datasets, amounting for a volumetric error of less than 10% which is comparable to pure ALS-campaigns. Larger errors were estimated for complex terrain with low scanning resolutions. A particular problem in data processing was the low and dense shrub vegetation in the study area which required a specifically adapted filter algorithm. An insufficient ground representation was observed for the ALS-data overestimating ground heights for averaged 70 cm. Despite these limitations, the approach proved to be suitable for accurate extreme event quantification.The starting zones of the debris flows lie at the bedrock-debris interface where runoff is concentrated. Volumes of 5000 to 12,000 m³ were assessed. Volume estimation worked better for the erosional than for the depositional features; this is because the erosional gullies are relatively deep and the calculation is not affected by pre-event vegetation. While erosion and sedimentation are balanced for one of the three catchments investigated, the deposited volumes are higher than the detected eroded volumes for the other two. The reasons are not fully understood. The magnitude of the flows was determined by catchment size, topographical characteristics and deforestation by a major wildfire in 1946.     

GIS技术和水热平衡模型在古湖泊水文重建研究中的应用--以石羊河流域为例

首次利用GIS技术并结合沉积学研究结果,计算全新世两个时段石羊河流域终闾湖泊的面积,建立石羊河流域水热平衡模型,进而恢复全新世两个时期的降水量。     

Positional accuracy and measurement error in digital databases of land use: an empirical study

This paper discusses the issues of positional accuracy and measurement error in the context of a large empirical study of landscape change in England and Wales. The epsilon band model of digitizing accuracy is used to make estimates of the levels of positional uncertainty and measurement error that is due to digitizing polygon outlines. The degree of error expected had the same polygons been captured in raster format is then determined. These results prompt a general discussion of the nature of error in spatial databases.     

Traveltime measurements from noise correlation: stability and detection of instrumental time-shifts

We test the feasibility of using Green's functions extracted from records of ambient seismic noise to monitor temporal changes in the Earth crust properties by repeated measurements at regional distances. We use about 11 yr of continuous recordings to extract surface waves between three pairs of stations in California. The correlations are computed in a moving 1-month window and we analyse the temporal evolution of measured interstation traveltimes. The comparison of the arrival times in the positive and negative correlation time of Rayleigh and Love waves allows us to separate time-shifts associated with any form of physical change in the medium, those resulting from clock drift or other instrumental errors, and those due to change in the localization of the noise sources. This separation is based on the principle of time symmetry. When possible, we perform our analysis in two different period bands: 5–10 and 10–20 s. The results indicate that significant instrumental time errors (0.5 s) are present in the data. These time-shifts can be measured and tested by closure relation and finally corrected independently of any velocity model. The traveltime series show a periodic oscillation that we interpret as the signature of the seasonal variation of the region of origin of the seismic noise. Between 1999 and 2005, the final arrival time fluctuations have a variance of the order of 0.01 s. This allows us to measure interstation traveltimes with errors smaller than 0.3 per cent of the interstation traveltime and smaller than 1 per cent of the used wave period. This level of accuracy was not sufficient to detect clear physical variation of crustal velocity during the considered 11 yr between the three stations in California. Such changes may be more easily detectable when considering pairs of stations more closely located to each other and in the vicinity of tectonically active faults or volcanoes.     

An estimate of hypocentre location accuracy in a large network: possible implications for tectonic studies in Italy

Data recorded by the Italian Telemetered Seismic Network (ITSN) of the Istituto Nazionale di Geofisica (ING) have been widely used in recent years to image slab structures and to find evidence for active processes along the Italian Peninsula. However, the use of seismic data for geostructural purposes may be affected by the well-known trade-off between earthquake location and seismic-velocity parameters. Furthermore, the confidence ellipse predicted by standard procedures may be inadequate for the representation of the probable error of a computed localization. This paper evaluates the probable errors on the hypocentre determinations of the seismic events recorded by the ITSN, using a Monte Carlo method.
We compute synthetic arrival times using a 1-D velocity model appropriate as an average for the Italian area. The hypocentres used are all those recorded by the ITSN during the period January 1992 to March 1994 (1972 events). Station locations are those of the current ITSN configuration. The synthetic arrival times are perturbed with a Gaussian distribution of errors and input to ING's standard hypocentral location procedure, but using crustal velocities differing by 10 per cent from those used to generate them. Each simulation is repeated at least 30 times. Average absolute shifts of hypocentres are assessed in grid cells of linear dimension 33 km covering the whole Italian region.
For regions within the ITSN, shifts are typically 5–10 km in location and up to 20 km in depth. However, for offshore and coastal regions, they are much greater: 50 km or more in both location and depth (far exceeding the equivalent uncertainties quoted by ING bulletins). Possible consequences of this are highlighted by producing a cross-section of subcrustal hypocentres from the Adriatic to the Tyrrhenian Sea, where the large uncertainty in depth precludes any confident interpretation of dipping tectonic features.     

A TEST FOR RANDOMNESS OF DIRECTIONS

i
The 5 per cent and 1 per cent significance points are given for a test of randomness of unit vectors in three dimensions. The test has been designed for use in the analysis of palaeomagnetic data.