Intercomparison of measurements of bulk snow density and water equivalent of snow cover with snow core samplers: Instrumental bias and variability induced by observers     

J. Ignacio López-Moreno  Leena Leppänen  Bartłomiej Luks  Ladislav Holko  Ghislain Picard  Alba Sanmiguel-Vallelado  Esteban Alonso-González  David C. Finger  Ali N. Arslan  Katalin Gillemot  Aynur Sensoy  Arda Sorman  M. Cansaran Ertaş  Steven R. Fassnacht  Charles Fierz  Christoph Marty 《水文研究》2020,34(14):3120-3133

Manually collected snow data are often considered as ground truth for many applications such as climatological or hydrological studies. However, there are many sources of uncertainty that are not quantified in detail. For the determination of water equivalent of snow cover (SWE), different snow core samplers and scales are used, but they are all based on the same measurement principle. We conducted two field campaigns with 9 samplers commonly used in observational measurements and research in Europe and northern America to better quantify uncertainties when measuring depth, density and SWE with core samplers. During the first campaign, as a first approach to distinguish snow variability measured at the plot and at the point scale, repeated measurements were taken along two 20 m long snow pits. The results revealed a much higher variability of SWE at the plot scale (resulting from both natural variability and instrumental bias) compared to repeated measurements at the same spot (resulting mostly from error induced by observers or very small scale variability of snow depth). The exceptionally homogeneous snowpack found in the second campaign permitted to almost neglect the natural variability of the snowpack properties and focus on the separation between instrumental bias and error induced by observers. Reported uncertainties refer to a shallow, homogeneous tundra-taiga snowpack less than 1 m deep (loose, mostly recrystallised snow and no wind impact). Under such measurement conditions, the uncertainty in bulk snow density estimation is about 5% for an individual instrument and is close to 10% among different instruments. Results confirmed that instrumental bias exceeded both the natural variability and the error induced by observers, even in the case when observers were not familiar with a given snow core sampler.  相似文献   

An on Orbit Determination of Point Spread Functions for the <Emphasis Type="Italic">Interface Region Imaging Spectrograph</Emphasis>     

Hans Courrier  Charles Kankelborg  Bart De Pontieu  Jean-Pierre Wülser 《Solar physics》2018,293(9):125

Using the 2016 Mercury transit of the Sun, we characterize on orbit spatial point spread functions (PSFs) for the Near- (NUV) and Far- (FUV) Ultra-Violet spectrograph channels of NASA’s Interface Region Imaging Spectrograph (IRIS). A semi-blind Richardson–Lucy deconvolution method is used to estimate PSFs for each channel. Corresponding estimates of Modulation Transfer Functions (MTFs) indicate resolution of 2.47 cycles/arcsec in the NUV channel near 2796 Å and 2.55 cycles/arcsec near 2814 Å. In the short (\({\approx}\,1336~\mathring{\mathrm{A}}\)) and long (\({\approx}\,1394~\mathring{\mathrm{A}}\)) wavelength FUV channels, our MTFs show pixel-limited resolution (3.0 cycles/arcsec). The PSF estimates perform well under deconvolution, removing or significantly reducing instrument artifacts in the Mercury transit spectra. The usefulness of the PSFs is demonstrated in a case study of an isolated explosive event. PSF estimates and deconvolution routines are provided through a SolarSoft module.  相似文献   

Analytical queries on semantic trajectories using graph databases     

Leticia I. Gmez  Bart Kuijpers  Alejandro A. Vaisman 《Transactions in GIS》2019,23(5):1078-1101

This article studies the analysis of moving object data collected by location‐aware devices, such as GPS, using graph databases. Such raw trajectories can be transformed into so‐called semantic trajectories, which are sequences of stops that occur at “places of interest.” Trajectory data analysis can be enriched if spatial and non‐spatial contextual data associated with the moving objects are taken into account, and aggregation of trajectory data can reveal hidden patterns within such data. When trajectory data are stored in relational databases, there is an “impedance mismatch” between the representation and storage models. Graphs in which the nodes and edges are annotated with properties are gaining increasing interest to model a variety of networks. Therefore, this article proposes the use of graph databases (Neo4j in this case) to represent and store trajectory data, which can thus be analyzed at different aggregation levels using graph query languages (Cypher, for Neo4j). Through a real‐world public data case study, the article shows that trajectory queries are expressed more naturally on the graph‐based representation than over the relational alternative, and perform better in many typical cases.  相似文献   

Identifying slope processes over time and their imprint in soils of medium‐high mountains of Central Europe (the Karkonosze Mountains,Poland)          下载免费PDF全文

Jaroslaw Waroszewski  Markus Egli  Dagmar Brandová  Marcus Christl  Cezary Kabala  Malgorzata Malkiewicz  Jakub Kierczak  Bartłomiej Glina  Paweł Jezierski 《地球表面变化过程与地形》2018,43(6):1195-1212

Soils in mountainous areas are often polygenetic, developed in slope covers that relate to glacial and periglacial activities of the Pleistocene and Holocene and reflect climatic variations. Landscape development during the Holocene may have been influenced by erosion/solifluction that often started after the Holocene climatic optimum. To trace back soil evolution and its timing, we applied a multi‐methodological approach. This approach helped us to outline scenario of soil transformation. According to our results, some aeolian input must have occurred in the late Pleistocene. During that time and the early Holocene, the soils most likely had features of Cryosols or Leptosols. Physico‐chemical and mineralogical analyses have indicated that the material was denudated (between late Boreal to the Atlantic) from the ridge and upper‐slope positions forming a colluvium at mid‐slope positions. Later, during the Sub‐Boreal, mass wasting of the remains of silt material deposited at the end of the Pleistocene age on the ridge top seems to have occurred. In addition, the cool and moist conditions caused the deposition of a colluvium at the lower‐slope positions. The next phase was characterized by the transformation of Leptosols/Cambisols into Podzols at upper‐slope or shoulder positions and to Albic Cambisols at mid‐slope positions. During the Sub‐Boreal period, Stagnosols started to form at the lower part of the slope catena. Overall, the highest erosion rates were calculated at the upper‐slope position and the lowest rates at mid‐slope sites. Berylium‐10 (¹⁰Be) data showed that the Bs, BC/C were covered during the Holocene by a colluvium with a different geological composition which complicated the calculation of erosion or accumulation rates. The interpretation of erosion and accumulation rates in such multi‐layered materials may, therefore, be hampered. However, the multi‐methodological reconstruction we applied shed light on the soil and landscape evolution of the eastern Karkonosze Mountains. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Examining the Use of USEPA's Generic Attenuation Factor in Determining Groundwater Screening Levels for Vapor Intrusion          下载免费PDF全文

Yijun Yao  Iason Verginelli  Eric M. Suuberg  Bart Eklund 《Ground Water Monitoring & Remediation》2018,38(2):79-89

A value of 0.001 is recommended by the United States Environmental Protection Agency (USEPA) for its groundwater‐to‐indoor air Generic Attenuation Factor (GAFG), used in assessing potential vapor intrusion (VI) impacts to indoor air, given measured groundwater concentrations of volatile chemicals of concern (e.g., chlorinated solvents). The GAFG can, in turn, be used for developing groundwater screening levels for VI given target indoor air quality screening levels. In this study, we examine the validity and applicability of the GAFG both for predicting indoor air impacts and for determining groundwater screening levels. This is done using both analysis of published data and screening model calculations. Among the 774 total paired groundwater‐indoor air measurements in the USEPA's VI database (which were used by that agency to generate the GAFG) we found that there are 427 pairs for which a single groundwater measurement or interpolated value was applied to multiple buildings. In one case, up to 73 buildings were associated with a single interpolated groundwater value and in another case up to 15 buildings were associated with a single groundwater measurement (i.e., that the indoor air contaminant concentrations in all of the associated buildings were influenced by the concentration determined at a single point). In more than 70% of the cases (390 of 536 paired measurements in which horizontal building‐monitoring well distance was recorded) the monitoring wells were located more than 30 m (and one up to over 200 m) from the associated buildings. In a few cases, the measurements in the database even improbably implied that soil gas contaminant concentrations increased, rather than decreased, in an upward direction from a contaminant source to a foundation slab. Such observations indicate problematic source characterization within the data set used to generate the GAFG, and some indicate the possibility of a significant influence of a preferential contaminant pathway. While the inherent value of the USEPA database itself is not being questioned here, the above facts raise the very real possibility that the recommended groundwater attenuation factors are being influenced by variables or conditions that have not thus far been fully accounted for. In addition, the predicted groundwater attenuation factors often fall far beyond the upper limits of predictions from mathematical models of VI, ranging from screening models to detailed computational fluid dynamic models. All these models are based on the same fundamental conceptual site model, involving a vadose zone vapor transport pathway starting at an underlying uniform groundwater source and leading to the foundation of a building of concern. According to the analysis presented here, we believe that for scenarios for which such a “traditional” VI pathway is appropriate, 10^?4 is a more appropriately conservative generic groundwater to indoor air attenuation factor than is the EPA‐recommended 10^?3. This is based both on the statistical analysis of USEPA's VI database, as well as the traditional mathematical models of VI. This result has been validated by comparison with results from some well‐documented field studies.  相似文献   

Preliminary results of a finite-element,multi-scale model of the Mahakam Delta (Indonesia)   总被引：1，自引：1，他引：0  

Benjamin de Brye  Sébastien Schellen  Maximiliano Sassi  Bart Vermeulen  Tuomas Kärnä  Eric Deleersnijder  Ton Hoitink 《Ocean Dynamics》2011,61(8):1107-1120

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The Middle Miocene to Recent Davis Strait Drift Complex: implications for Arctic�CAtlantic water exchange     

Tove Nielsen  Claus Andersen  Paul C. Knutz  Antoon Kuijpers 《Geo-Marine Letters》2011,31(5-6):419-426

A large-scale contourite drift complex has been recognised on multi-channel 2D reflection seismic data acquired in the south-eastern Davis Strait and adjacent Labrador Sea slope offshore West Greenland between 63°?C66°N. Based on well-tie data, the drift complex developed from the Middle Miocene to the Recent. It has been mapped in a wide variety of water depths ranging from about 700?m, at a NNW-ESE-elongated crest located above structural highs in the Davis Strait, to more than 2,000?m beyond the slope to the Labrador Sea. The overall drift geometry has been described by subdivision into two first-order seismic units, enabling the generation of time-isochore maps. The reflection patterns demonstrating current-related deposition are illustrated by seismic examples. The time-isochores of the two first-order seismic units show lateral changes in their depocentres: the lower unit is absent in a zone slightly displaced south-westwards of the present-day crest, indicating changes in the prevailing deepwater current system during the Early Pliocene. The observations can be explained by two alternative palaeoceanographic scenarios: (1) either the present-day oceanographic setting with Arctic?CAtlantic water exchange across the Davis Strait was largely established by the mid-Miocene, with only minor adjustments during the Early Pliocene caused by tectonic movements, or (2) it became established during the Early Pliocene as a consequence of enhanced northward flow across the Davis Strait due to lowering of the sill depth.  相似文献   

3D modeling of light interception in heterogeneous forest canopies using ground-based LiDAR data     

Dimitry Van der Zande  Jan Stuckens  Willem W. Verstraeten  Simone Mereu  Bart Muys  Pol Coppin 《International Journal of Applied Earth Observation and Geoinformation》2011

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Centennial scale benthic foraminiferal record of late Holocene oceanographic variability in Disko Bugt,West Greenland     

K. Perner  M. Moros  J.M. Lloyd  A. Kuijpers  R.J. Telford  J. Harff 《Quaternary Science Reviews》2011,30(19-20):2815-2826

A new centennial scale benthic foraminiferal record of late Holocene climate variability and oceanographic changes off West Greenland (Disko Bugt) highlights substantial subsurface water mass changes (e.g. temperature and salinity) of the West Greenland Current (WGC) over the past 3.6 ka BP. Benthic foraminifera reveal a long-term late Holocene cooling trend, which may be attributed to increased advection of cold, low-salinity water masses derived from the East Greenland Current (EGC). Cooling becomes most pronounced from c. 1.7 ka BP onwards. At this point the calcareous Atlantic benthic foraminiferal fauna decrease significantly and is replaced by an agglutinated Arctic fauna. Superimposed on this cooling trend, centennial scale variability in the WGC reveals a marked cold phase at c. 2.5 ka BP, which may correspond to the 2.7 ka BP cooling-event recorded in marine and terrestrial archives elsewhere in the North Atlantic region. A warm phase recognized at c. 1.8 ka BP is likely to correspond to the ‘Roman Warm Period’ and represents the warmest bottom water conditions. During the time period of the ‘Medieval Climate Anomaly’ we observe only a slight warming of the WGC. A progressively more dominant cold water contribution from the EGC on the WGC is documented by the prominent rise in abundance of agglutinated Arctic water species from 0.9 ka BP onwards. This cooling event culminates at c. 0.3 ka BP and represents the coldest episode of the ‘Little Ice Age’.Gradually increased influence of cold, low-salinity water masses derived from the EGC may be linked to enhanced advection of Polar and Arctic water by the EGC. These changes are possibly associated with a reported shift in the large-scale North Atlantic Oscillation atmospheric circulation pattern towards a more frequent negative North Atlantic Oscillation mode during the late Holocene.  相似文献   

西格陵兰Disko湾表层沉积硅藻组合研究          下载免费PDF全文

沙龙滨  任健  蒋辉  Kuijpers A 《极地研究》2008,20(3):229-239

本文分析了西格陵兰Disko湾的表层沉积物硅藻,发现并统计了分属于39个属的78个硅藻种及其变种。应用对应分析方法,对Disko湾表层沉积硅藻组合进行了分类:组合Ⅰ为Fragilariopsis cylindrus-Fragilariopsis oceanica组合,主要分布在西格陵兰Disko湾南部的近岸和外海处;组合Ⅱ为Detonula confervaceae休眠孢子-Thalassiosira nordenskioeldii组合,都分布在Dis-ko湾北部海域。其中,根据海流等环境要素的不同,组合Ⅰ又可进一步划分为两个亚区:组合Ⅰa为F.cylindrus-F.oceanica-Pauliella taeniata组合,主要分布于沿岸海区;组合Ⅰb为F.cy-lindrus-F.oceanica-Thalassiosira antarcticavar.borealis休眠孢子-Thalassiosiracf.antarcticavar.borealis组合,分布于外海区域。  相似文献