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1.
Accuracy assessment of digital elevation models by means of robust statistical methods 总被引:3,自引:0,他引:3
Measures for the accuracy assessment of Digital Elevation Models (DEMs) are discussed and characteristics of DEMs derived from laser scanning and automated photogrammetry are presented. Such DEMs are very dense and relatively accurate in open terrain. Built-up and wooded areas, however, need automated filtering and classification in order to generate terrain (bare earth) data when Digital Terrain Models (DTMs) have to be produced. Automated processing of the raw data is not always successful. Systematic errors and many outliers at both methods (laser scanning and digital photogrammetry) may therefore be present in the data sets. We discuss requirements for the reference data with respect to accuracy and propose robust statistical methods as accuracy measures. Their use is illustrated by application at four practical examples. It is concluded that measures such as median, normalized median absolute deviation, and sample quantiles should be used in the accuracy assessment of such DEMs. Furthermore, the question is discussed how large a sample size is needed in order to obtain sufficiently precise estimates of the new accuracy measures and relevant formulae are presented. 相似文献
2.
Joachim Köppen 《Astrophysics and Space Science》2003,284(2):837-840
Representative results from a comparison of the chemical evolution of spherical collapse models without and with a intercloud
medium are presented. The hot metal-rich gas distributes quickly the metals produced in supernovae throughout the galaxy,
thus leading to a more homogeneous chemical evolution and flatter metallicity gradients in the gas and the stars. The stellar
population is somewhat less concentrated towards the centre. The strong outflow results in a substantial loss of metals from
the galaxy to its surroundings, and a lower effective yield in the galaxy.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
Ralph D. Lorenz 《Meteoritics & planetary science》2004,39(4):617-623
Abstract— A model for an impact ejecta landform peculiar to Saturn's moon Titan is presented. Expansion of the ejecta plume from moderate‐sized craters is constrained by Titan's thick atmosphere. Much of the plume is collimated along the incoming bolide's trajectory, as was observed for plumes from impacts on Jupiter of P/Shoemaker‐Levy‐9, but is retained as a linear, diagonal ejecta cloud, unlike on Venus where the plume “blows out.” On Titan, the blowout is suppressed because the vertically‐extended atmosphere requires a long wake to reach the vacuum of space, and the modest impact velocities mean plume expansion along the wake is slow enough to allow the wake to close off. Beyond the immediate ejecta blanket around the crater, distal ejecta is released into the atmosphere from an oblique line source: this material is winnowed by the zonal wind field to form streaks, with coarse radar‐bright particles transported less far than fine radar‐dark material. Thus, the ejecta form two distinct streaks faintly reminiscent of dual comet tails, a sharply W‐E radar‐dark one, and a less swept and sometimes comma‐shaped radar‐bright one. 相似文献
4.
Ralph D. Lorenz A. J. Timothy Jull Timothy D. Swindle Jonathan I. Lunine 《Meteoritics & planetary science》2002,37(6):867-874
Abstract— We explore the likely production and fate of 14C in the thick nitrogen atmosphere of Saturn's moon Titan and investigate the constraints that measurements of 14C might place on Titan's photochemical, atmospheric transport and surface‐atmosphere interaction processes. Titan's atmosphere is thick enough that cosmic‐ray flux limits the production of 14C: absence of a strong magnetic field and the increased distance from the Sun suggest production rates of ?9 atom/cm2/s, ?4x higher than Earth. The fate and detectability of 14C depends on the chemical species into which it is incorporated: as methane it would be hopelessly diluted even in only the atmosphere. However, in the more likely case that the 14C attaches to the haze that rains out onto the surface (as tholin, HCN or acetylene and their polymers), haze in the atmosphere or recently deposited on the surface would be quite radioactive. Such radioactivity may lead to a significant enhancement in the electrical conductivity of the atmosphere which will be measured by the Huygens probe. Measurements with simple detectors on future missions could place useful constraints on the mass deposition rates of photochemical material on the surface and identify locations where surface deposits of such material are “freshest”. 相似文献
5.
Tidal inundation mapping under enhanced land subsidence in Semarang,Central Java Indonesia 总被引:3,自引:0,他引:3
Tidal inundation by high tide under enhanced land subsidence is a damaging phenomenon and a major threat to the Semarang urban
area in Indonesia. It impacts on economic activities, as well as the cost of an emergency program and causes interruption
of pubic services, danger of infectious diseases and injury to human lives. This study examines a spatial analysis tool on
the GIS-raster system for the tidal inundation mapping based on the subsidence-benchmark data and modified detail digital
elevation model. Neighborhood operation and iteration model as a spatial analysis tool have been applied in order to calculate
the encroachment of the tidal inundation on the coastal area. The resulting map shows that the tidal flood spreads to the
lowland area and causes the inundation of coastal settlement, infrastructure, as well as productive agricultural land, i.e.,
the fish-pond area. The monitoring of the vulnerable area due to the tidal inundation under the scenario of extended land
subsidence plays an important role in long-term coastal zone management in Semarang. 相似文献
6.
Dieter Lorenz 《Pure and Applied Geophysics》1962,53(1):143-158
Zusammenfassung Es wird über eine photographische Methode berichtet, die gestattet, die Verteilung der Himmelsstrahlung zu bestimmen. Der Himmel wird mit einer Weitwinkelkamera photographiert und die Aufnahmen werden mit einem Photometer ausgewertet. Über einen Graukeil, der auf das gleiche filmmaterial aufbelichtet und mit den Aufnahmen zusammen entwickelt wird, lassen sich die mit dem Photometer ermittelten Schwärzungswerte in (relative) Intensitätswerte der Himmelsstrahlung umrechnen. Der durch das Photoobjektiv bedingte Helligkeitsabfall von der Bildmitte aus nach den Bildrändern zu wird experimentell ermittelt und als Korrektur an den Meßwerten angebracht. Die Intensitätsverteilung der Himmelsstrahlung während der totalen Sonnenfinsternis am 15. Februar 1961 in Viareggio (Norditalien), am Abend zuvor und am Folgetag wird wiedergegeben und diskutiert. Während der totalen Verfinsterung spiegelt sich insbesondere die Wanderung des Mondschattens relativ zum Beobachtungsort in den Darstellungen wieder. Während der partiellen Verfinsterung ist dagegen die relative Helligkeitsverteilung praktisch die gleiche wie bei unverfinsterter Sonne.
Summary A photographic method is described which permits to determinate the distribution of the sky radiation. The sky is photographed by a wide angle camera and the resulting pictures are evaluated by a photometer. A photometric step wedge copied on a film of the same type and number is developed together with the pictures. Then the density values measured by the photometer can be transformed into (relative) intensity values of the sky radiation. The decrease in brightness from the centre of the picture to the rim caused by the photographic lens is determined experimentally and is taken into account as a correction to the density values. The distribution of intensity of the sky radiation in Viareggio (North Italy) during the total eclipse of the sun on the 15th of february 1961, on the previous evening and on the following day are shown and discussed. During the total eclipse especially the migration of the moon's shadow in relation to the observation point is clearly defined. During the partial eclipse, however, practically the same relative distribution of sky radiation is found as without eclipse.相似文献
7.
Modelling and forecasting long-term dynamics of Western Baltic macrobenthic fauna in relation to climate signals and environmental change 总被引:1,自引:0,他引:1
Long-term macrobenthos data from Kiel Bight in the Western Baltic collected between 1968 and 2000 have been correlated with the winter NAO index (North Atlantic Oscillation Index) and other environmental data such as temperature, salinity and oxygen content in the bottom water in order to detect systematic patterns related to so far unexplained abiotic signals in the dynamics of zoobenthic species assemblages. The benthos data come from a cluster of five stations (Süderfahrt/ Millionenviertel) in Kiel Bay. Our investigations concentrated on the macrobenthic dynamics with a focus on the number of species m− 2 (species richness). Using logarithms and the time series analysis approach of Box/Jenkins (ARIMA modelling, transfer function modelling) it was shown that species richness was strongly influenced by the winter NAO (adjusted for a linear time trend within the 1968-2000 period) and salinity (with a shift/lag of four years). Bootstrapping experiments (i.e. sampling from the error process) and analysis of prediction power (by means of the one- or more-years leaving-out method) showed that the parameter estimates behaved in a stable way, leading to a relatively robust model. 相似文献
8.
9.
In the present study, long-term exposure to PCB resulted in marked induction of the xenobiotic biotransformation enzymes UDP glucuronosyl transferase, glutathione transferase and DT-diaphorase (measured as menadione reductase and DCPIP reductase) in rainbow trout 15 or 20 weeks post-injection during the experimental period. The increase of the phase II enzymes were paralleled by a marked increase of the glutathione reductase activity. These results indicate that prolonged exposure to PCB results in increased production of organo-radicals. 相似文献
10.