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101.
An Operational Application of Automatic Feature Extraction: The Measurement of Cracks in Concrete Structures 总被引:1,自引:1,他引:1
Paul Dare Harry Hanley Clive Fraser Björn Riedel & Wolfgang Niemeier 《The Photogrammetric Record》2002,17(99):453-464
An understanding of the evolution of cracks in concrete structures due to long term natural deformation is important to civil engineers, but quantitative measurements can be difficult to make. However, digital imaging offers a potential solution. This short paper illustrates the operational application of automated image processing techniques for accurate, multi-temporal crack measurements. The first part of this paper provides an overview of automatic feature extraction, essential for automatic crack detection. The latter part describes the methods developed for detecting and measuring cracks. Due to the long term nature of the application, operational results have yet to be finalised, although sample results are presented 相似文献
102.
Melanie Jacobs Douglas P. Nowacek Donald J. Gerhart Gail Cannon Stephen Nowicki Richard B. Forward 《Estuaries and Coasts》1993,16(2):241-246
Four vocalizations (whistles, buzzes, quacks, and pops) were quantified during three behavioral categories (socializing, traveling, and feeding) of the bottlenose dolphin in the Newport River Estuary, North Carolina. This study tested the hypothesis that specific vocalizations of dolphins in this area are associated with specific behavioral categories during the summer and fall. Approximately twice the total number of vocalizations per unit time occurred during the fall as compared to the summer. Each type of vocalization had a distinctive and consistent acoustical structure. The relative frequency of the different vocalization types was significantly dependent on the behavior of the dolphins. Pops were consistently associated with feeding, quacks with socializing, and buzzes with traveling. Whistles, the most common vocalization, were associated with traveling and feeding during the summer and socializing in the fall. Dolphins spent more time involved in undirected activity (socialization) during the summer but spent more time traveling in search of food and feeding during the fall in preparation for migration out of the estuary and movement south. 相似文献
103.
Questions remain as to the nature of climatic change through the last glacial–interglacial transition in the eastern Mediterranean region, particularly the relative contribution of evaporation and precipitation to regional water balance. Here changes in oxygen isotope values through this time period from Eski Acıgöl, a crater lake in central Turkey, are investigated using hydrological and isotope mass balance models. These allow changes in evaporation and precipitation to be quantified and their relative importance evaluated. We show that it is the volumetric flux rate of water passing through the lake system and not the precipitation-to-evaporation ratio per se which controlled the stable isotope record in Eski Acıgöl. Early Holocene precipitation is shown to be much greater than that during both the latter part of the last glaciation and the present day. We test these calculated values against other records in the same region, firstly with other lake records in Anatolia, the Konya basin and Lake Van, and secondly with isotope-inferred palaeo-precipitation data from Soreq cave in Israel. This reveals a contrast between pre- and post-LGM precipitation values in Turkey (wetter and drier, respectively) and also suggests that during the last glacial–interglacial transition there was a more marked precipitation gradient than at present between northern/interior and southern/coastal parts of the eastern Mediterranean region. 相似文献
104.
Dany Savard Sarah Dare L. Paul Bédard Sarah-Jane Barnes 《Geostandards and Geoanalytical Research》2023,47(2):243-265
Although in situ analysis by LA-ICP-MS is considered a rapid technique with minimal sample preparation and data reduction, mapping areas of millimetres in size using a small beam (< 15 μm) can be time consuming (several hours) when a quadrupole ICP-MS is used. In addition, fully quantitative imaging using internal standardisation by LA-ICP-MS is challenging in samples with more than one mineral phase present due to varying ablation rates. A new protocol for the quantification of multiple coexisting phases, mapped at a rate of about 12 mm2 h-1 and a resolution of 12 μm × 12 μm per pixel, is presented. The protocol allows mapping of most atomic masses, ranging from 23Na to 238U, using a time-of-flight mass spectrometer (ICP-ToF-MS, TOFWERK) connected to a 193 nm excimer laser. A fast-funnel device was successfully used to increase the aerosol transport speed, reducing the time usually required for mapping by a factor of about ten compared with a quadrupole ICP-MS. The lower limits of detection for mid and heavy masses are in the range 0.1–10 μg g-1, allowing determination of trace to ultra-trace elements. The presented protocol is intended to be a routine analytical tool that can provide greater access to the spatial distribution of major and trace elements in geological materials. 相似文献
105.
106.
Tropospheric delay gradients from numerical weather prediction models: effects on GPS estimated parameters 总被引:3,自引:1,他引:2
Several numerical weather prediction (NWP) models provide information on the 3D state of the neutral atmosphere which has
enabled GNSS researchers to have improved a priori information of the delay induced in the GNSS signals. However, the quality
of weather models on the one hand and computational difficulties on the other, are motivations to develop an algorithm based
partly on NWP models, while still estimating the remaining residual delay through GNSS processing strategies. An algorithm
has been developed to estimate horizontal delay gradients from Meteorological Service of Canada NWP models. The GNSS software
“Bernese” has also been modified to handle these gradients, as well as zenith delay and mapping functions based on NWP models
in phase and code observation equations. Month-long precise point positioning results show strong correlation between north–south
hydrostatic gradients and latitude differences, with significant but less strong correlation with the height and zenith total
delay parameters. The longitude components were not sensitive to the implementation of gradients. High precision GNSS applications
such as long term geodynamics studies, realization of terrestrial reference frames and climatology and consequential interpretations
may be affected by ignoring the asymmetry of the neutral atmosphere. In addition to estimating the gradients, implementing
a priori information on gradients in the processing software may have an impact on estimated results and consequential interpretations. 相似文献
107.
Everett L. Shock Melanie Holland D’Arcy Meyer-Dombard Jan P. Amend Tobias P. Fischer 《Geochimica et cosmochimica acta》2010,74(14):4005-4845
Combining analytical data from hot spring samples with thermodynamic calculations permits a quantitative assessment of the availability and ranking of various potential sources of inorganic chemical energy that may support microbial life in hydrothermal ecosystems. Yellowstone hot springs of diverse geochemical composition, ranging in pH from <2 to >9 were chosen for this study, and dozens of samples were collected during three field seasons. Field measurements of dissolved oxygen, nitrate, nitrite, total ammonia, total sulfide, alkalinity, and ferrous iron were combined with laboratory analyses of sulfate and other major ions from water samples, and carbon dioxide, hydrogen, methane, and carbon monoxide in gas samples to evaluate activity products for ∼300 coupled oxidation-reduction reactions. Comparison of activity products and independently calculated equilibrium constants leads to values of the chemical affinity for each of the reactions, which quantifies how far each reaction is from equilibrium. Affinities, in turn, show systematic behavior that is independent of temperature but can be correlated with pH of the hot springs as a proxy for the full spectrum of geochemical variability. Many affinities are slightly to somewhat dependent on pH, while others are dramatically influenced by changes in chemical composition. All reactions involving dissolved oxygen as the electron acceptor are potential energy sources in all hot spring samples collected, but the ranking of dominant electron donors changes from ferrous iron, and sulfur at high pH to carbon monoxide, hydrogen, and magnetite as pH decreases. There is a general trend of decreasing energy yields depending on electron acceptors that follows the sequence: O2(aq) > NO3− ≈ NO2− ≈ S > pyrite ≈ SO4−2 ≈ CO(g) ≈ CO2(g) at high pH, and O2(aq) ≈ magnetite > hematite ≈ goethite > NO3− ≈ NO2− ≈ S ≈ pyrite ≈ SO4−2 at low pH. Many reactions that are favorable sources of chemical energy at one set of geochemical conditions fail to provide energy at other conditions, and vice versa. This results in energy profiles supplied by geochemical processes that provide fundamentally different foundations for chemotrophic microbial communities as composition changes. 相似文献
108.
109.
Angela L. Lamb Melanie J. Leng Henry F. Lamb Richard J. Telford Mohammed Umer Mohammed 《Quaternary Science Reviews》2002,21(20-22)
A comparison of a 6450 14C yr δ18O and δ13C record of authigenic calcite from Lake Awassa, Ethiopia, with other proxy climate records in the area suggests that the lake records long-term regional climate changes. Co-varying and increasing δ18O and δ13C values from 4800 BP suggest an aridification of climate after the early Holocene insolation maximum. After 4000 BP, humid conditions return until after 2800 BP when δ18O increases again, reflecting more arid conditions recorded elsewhere in Ethiopia. In addition to these long-term changes, there are abrupt decreases in both δ18Ocalcite and δ13Ccalcite immediately after tephra layers. The likeliest explanation for these abrupt decreases in isotopes is the effect of tephra on the lake's catchment vegetation. δ18O, δ13C and lake-level measurements from Lake Awassa since the 1970s suggest that the lake is currently isotopically sensitive to short-term (annual–decadal) climate change. However, during this period, the catchment has undergone progressive deforestation that may have caused an increase in runoff. Caution is therefore required when reconstructing palaeoclimates as a contemporary lake may not always be a good analogue for lake hydrology in the past. 相似文献
110.
Andrea Lübben Olaf Dellwig Sandra Koch Melanie Beck Thomas H. Badewien Sibylle Fischer Rainer Reuter 《Ocean Dynamics》2009,59(2):263-275
The spatial and temporal distributions of chromophoric dissolved organic matter (CDOM) and dissolved organic carbon (DOC)
was studied in the East-Frisian Wadden Sea (Southern North Sea) during several cruises between 2002 and 2005. The spatial
distribution of CDOM in the German Bight shows a strong gradient towards the coast. Tidal and seasonal variations of dissolved
organic matter (DOM) identify freshwater discharge via flood-gates at the coastline and pore water efflux from tidal flat
sediments as the most important CDOM sources within the backbarrier area of the Island of Spiekeroog. However, the amount
and pattern of CDOM and DOC is strongly affected by various parameters, e.g. changes in the amount of terrestrial run-off,
precipitation, evaporation, biological activity and photooxidation. A decoupling of CDOM and DOC, especially during periods
of pronounced biological activity (algae blooms and microbial activity), is observed in spring and especially in summer. Mixing
of the endmembers freshwater, pore water, and open sea water results in the formation of a coastal transition zone. Whilst
an almost conservative behaviour during mixing is observed in winter, summer data point towards non-conservative mixing. 相似文献