Radiative effects of simulated cirrus clouds on top of a deep convective storm in METEOSAT second generation SEVIRI channels     

S. Melani  E. Cattani  V. Levizzani  M. Cervino  F. Torricella  M. J. Costa 《Meteorology and Atmospheric Physics》2003,83(1-2):109-122

Summary ?Cirrus clouds often form above intense convective storms due to several different mechanisms and affect the radiation field at the top of the atmosphere. Radiative transfer computations are performed to characterize these effects within the spectral bands of METEOSAT Second Generation’s (MSG) Spinning Enhanced Visible and InfraRed Imager (SEVIRI). Computations refer to five visible, near infrared and infrared MSG SEVIRI channels centered at 0.8, 1.6, 3.9, 10.8, and 12.0 μm. Reflectances and brightness temperatures are computed using the 1-D radiative transfer model STREAMER adopting simple parameterizations of the cloud layers and associated microphysical properties for the determination of the necessary optical properties. A sensitivity study is carried out by varying the cirrus ice crystal size and optical depth. The 1.6 and 3.9 μm channels reveal instrumental for the simultaneous detection of optical depth and crystal size of the cirrus layer. In particular, the results of the 3.9 μm channel show that the smaller the crystal size the higher the reflectance values. The computations provide interpretation clues on the phenomenon of ice crystal plumes on top of deep convective clouds, which are known to produce enhanced reflectivity signatures in the 3.7 μm channel of the Advanced Very High Resolution Radiometer (AVHRR). The sensitivity of the IR channels to cirrus cloud optical depth and ice crystal size is examined and the brightness temperature differences evaluated. Satellite observations and radiative transfer computations are at present the only way of studying such cloud features due to the unavailability of in situ aircraft measurements. Also Visiting Scientist at EUMETSAT, Darmstadt, Germany. Received March 13, 2002  相似文献   

Interaction of wind and cold-season hydrologic processes on erosion from complex topography following wildfire in sagebrush steppe     

Samantha P. Vega  C. Jason Williams  Erin S. Brooks  Frederick B. Pierson  Eva K. Strand  Peter R. Robichaud  Robert E. Brown  Mark S. Seyfried  Kathleen A. Lohse  Kayla Glossner  Jennifer L. Pierce  Clay Roehner 《地球表面变化过程与地形》2020,45(4):841-861

Wildfire is a natural component of sagebrush (Artemisia spp.) steppe rangelands that induces temporal shifts in plant community physiognomy, ground surface conditions, and erosion rates. Fire alteration of the vegetation structure and ground cover in these ecosystems commonly amplifies soil losses by wind- and water-driven erosion. Much of the fire-related erosion research for sagebrush steppe has focused on either erosion by wind over gentle terrain or water-driven erosion under high-intensity rainfall on complex topography. However, many sagebrush rangelands are geographically positioned in snow-dominated uplands with complex terrain in which runoff and sediment delivery occur primarily in winter months associated with cold-season hydrology. Current understanding is limited regarding fire effects on the interaction of wind- and cold-season hydrologic-driven erosion processes for these ecosystems. In this study, we evaluated fire impacts on vegetation, ground cover, soils, and erosion across spatial scales at a snow-dominated mountainous sagebrush site over a 2-year period post-fire. Vegetation, ground cover, and soil conditions were assessed at various plot scales (8 m² to 3.42 ha) through standard field measures. Erosion was quantified through a network of silt fences (n = 24) spanning hillslope and side channel or swale areas, ranging from 0.003 to 3.42 ha in size. Sediment delivery at the watershed scale (129 ha) was assessed by suspended sediment samples of streamflow through a drop-box v-notch weir. Wildfire consumed nearly all above-ground live vegetation at the site and resulted in more than 60% bare ground (bare soil, ash, and rock) in the immediate post-fire period. Widespread wind-driven sediment loading of swales was observed over the first month post-fire and extensive snow drifts were formed in these swales each winter season during the study. In the first year, sediment yields from north- and south-facing aspects averaged 0.99–8.62 t ha⁻¹ at the short-hillslope scale (~0.004 ha), 0.02–1.65 t ha⁻¹ at the long-hillslope scale (0.02–0.46 ha), and 0.24–0.71 t ha⁻¹ at the swale scale (0.65–3.42 ha), and watershed scale sediment yield was 2.47 t ha⁻¹. By the second year post fire, foliar cover exceeded 120% across the site, but bare ground remained more than 60%. Sediment yield in the second year was greatly reduced across short- to long-hillslope scales (0.02–0.04 t ha⁻¹), but was similar to first-year measures for swale plots (0.24–0.61 t ha⁻¹) and at the watershed scale (3.05 t ha⁻¹). Nearly all the sediment collected across all spatial scales was delivered during runoff events associated with cold-season hydrologic processes, including rain-on-snow, rain-on-frozen soils, and snowmelt runoff. Approximately 85–99% of annual sediment collected across all silt fence plots each year was from swales. The high levels of sediment delivered across hillslope to watershed scales in this study are attributed to observed preferential loading of fine sediments into swale channels by aeolian processes in the immediate post-fire period and subsequent flushing of these sediments by runoff from cold-season hydrologic processes. Our results suggest that the interaction of aeolian and cold-season hydrologic-driven erosion processes is an important component for consideration in post-fire erosion assessment and prediction and can have profound implications for soil loss from these ecosystems. © 2019 John Wiley & Sons, Ltd.  相似文献   

GeoNat v1.0: A dataset for natural feature mapping with artificial intelligence and supervised learning     

Samantha T. Arundel  Wenwen Li  Sizhe Wang 《Transactions in GIS》2020,24(3):556-572

Machine learning allows “the machine” to deduce the complex and sometimes unrecognized rules governing spatial systems, particularly topographic mapping, by exposing it to the end product. Often, the obstacle to this approach is the acquisition of many good and labeled training examples of the desired result. Such is the case with most types of natural features. To address such limitations, this research introduces GeoNat v1.0, a natural feature dataset, used to support artificial intelligence‐based mapping and automated detection of natural features under a supervised learning paradigm. The dataset was created by randomly selecting points from the U.S. Geological Survey’s Geographic Names Information System and includes approximately 200 examples each of 10 classes of natural features. Resulting data were tested in an object‐detection problem using a region‐based convolutional neural network. The object‐detection tests resulted in a 62% mean average precision as baseline results. Major challenges in developing training data in the geospatial domain, such as scale and geographical representativeness, are addressed in this article. We hope that the resulting dataset will be useful for a variety of applications and shed light on training data collection and labeling in the geospatial artificial intelligence domain.  相似文献   

Tigers, trees and Tharu: An analysis of community forestry in the buffer zone of the Royal Chitwan National Park, Nepal   总被引：1，自引：0，他引：1  

Samantha Jones 《Geoforum》2007,38(3):558-575

In the buffer zone of the Royal Chitwan National Park (RCNP), community forests represent a key land use to meet the objectives of the buffer zone concept. This article examines three diverse community forests surrounding the national park and explores how national policy has been mediated by emerging community forestry institutions to create different levels of resource access and benefit distribution both within and between local user groups. Mindful of recent critiques of community-based conservation, the analysis gives considerable attention to the dynamics of power relations and inequality. The extent to which property rights have been transferred to the local level is evaluated and to whom power has been devolved in the process is assessed. The distribution of benefits arising from community forestry is critically examined. It seems that the current system for community forestry creates sufficient incentives for local cooperation due to the potential for increased access to important resources and a high perception of ownership of community forests among the communities. However, emerging institutions vary in the extent to which they reproduce favourable resource access conditions for elites and benefit distribution does seem to be skewed in favour of the wealthy and higher castes, even where management practices on the surface appear fair. National policy creates sufficient but not necessary conditions for achieving downward accountability, transparency and fairness. Greater attention to these issues is needed for buffer zone community forestry to better serve the poor and marginalised populations within user groups.  相似文献   

Clearcutting and pine planting effects on nutrient concentrations and export in two mixed use headwater streams: Upper Coastal Plain,Southeastern USA          下载免费PDF全文

Samantha C. Marchman  Masato Miwa  William B. Summer  Scott Terrell  David G. Jones  S. Lynsey Scarbrough  C. Rhett Jackson 《水文研究》2015,29(1):13-28

Timber harvest temporarily increases water yield; however, relationships between hydrologic and nutrient chemistry changes have not been consistent. This study quantified the effects of forest harvesting and site preparation without fertilization and with modern best management practices on nutrient concentrations and yields in small headwater streams of the Southeastern Coastal Plain. We monitored two watershed pairs for 2 years prior to and 1 year following timber harvest and for 2 more years following site preparation and planting. Treatment watersheds were clearcut, and downstream portions of streamside management zones were thinned in Fall 2003. Site preparation (herbicide application and burning) and planting followed a year later. All operations followed 1999 Georgia forestry best management practices. Previously published research revealed a large increase in water yield following harvest. Nutrient concentrations varied significantly within and between monitoring periods, even in reference watersheds. Silvicultural activities had no discernible effect on phosphorus and ammonium concentrations; however, statistically significant increases in nitrate/nitrite (67–340 µg L⁻¹) and total nitrogen concentrations (100–400 µg L⁻¹) in treatment watersheds followed stand re‐establishment. Nutrient yields increased after timber harvest largely as a result of increased water yields, although increased nutrient yields were small relative to inter‐annual and inter‐watershed variability and variability. Annual water yield largely explained the variability in annual nitrogen and phosphorus export from reference and treatment streams (r² values from 0.65 to 0.98). High NO_x concentrations coming from an upstream agricultural area decreased 1600–1800 µg L⁻¹ over several hundred metres in the treatment streams by dilution, uptake or denitrification. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

MS 1512–cB58: A case study of star formation, metal enrichment and superwinds in Lyman break galaxies     

Max Pettini  Samantha A. Rix  Chuck C. Steidel  Matthew P. Hunt  Alice E. Shapley  Kurt L. Adelberger 《Astrophysics and Space Science》2002,281(1-2):461-466

Recent advances in instrumentation and observing techniques have made it possible to begin to study in detail the stellar populations and the interstellar media of galaxies at redshift z = 3, when the universe was still in its ‘teen years’. I illustrate recent progress in this field with the latest observations of the gravitationally lensed galaxy MS 1512- cB58. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

Contamination of sediments in the floodplain wetlands of the lower uMngeni River,Kwa-Zulu Natal,South Africa     

Samantha Naidoo  Srinivasan Pillay  Ajay Bissessur  Hari Ballabh  Delon Naicker 《Journal of Earth System Science》2018,127(3):39

This study describes the geochemical and physico-chemical characterization of contaminant status of six wetlands of the lower uMngeni River floodplain, KwaZulu-Natal Province, South Africa. At all sites, organic matter content, calcium carbonate and metal concentrations were highest within the fine-sediment dominated surface laminae, decreasing with depth. Exceptions were displayed by arsenic (As), nickel (Ni) and vanadium (V), presumed to be derived from normal geochemical processes. Geochemical indicies indicated high contamination factors for lead (Pb) and V, pointing to moderate anthropogenic metal pollution contribution. Most conspicuous are the contamination high factors for Pb across most sites. Fe and Pb contamination is ubiquitous in all surface laminae, with contamination factors being either border-line, moderate or of high contamination. Enrichment factors for As, Mn and P at site S6 indicate possible anthropogenic sources. The data also shows a possibility of anthropogenic input of P and Zn at site S3. Apart from the enrichment factors established for Ni across all sites, all other metals indicate some degree of enrichment. A range of variable results for the mid to deeper laminae are indicative of natural processes with some human influence. Results of ANOVA confirm the above. Principal component analysis reveals a 46.4% variance from component 1 elements (Al, Ca, Cr, Cu, Fe, Mg, Mn and Zn) and a 17.8% variance from component 2 (Al, Cu and Fe). Given the rapid rate of development in this region, the protection of these floodplain wetlands must receive high conservation priority from the local municipality.  相似文献   

Thallium Mass Fraction and Stable Isotope Ratios of Sixteen Geological Reference Materials          下载免费PDF全文

Alex Brett  Julie Prytulak  Samantha J. Hammond  Mark Rehkämper 《Geostandards and Geoanalytical Research》2018,42(3):339-360

Thallium stable isotope ratio and mass fraction measurements were performed on sixteen geological reference materials spanning three orders of magnitude in thallium mass fraction, including both whole rock and partially separated mineral powders. For stable isotope ratio measurements, a minimum of three independent digestions of each reference material was obtained. High‐precision trace element measurements (including Tl) were also performed for the majority of these RMs. The range of Tl mass fractions represented is 10 ng g^?1 to 16 μg g^?1, and Tl stable isotope ratios (reported for historical reasons as ε²⁰⁵Tl relative to NIST SRM 997) span the range ?4 to +2. With the exception – attributed to between‐bottle heterogeneity – of G‐2, the majority of data are in good agreement with published or certified values, where available. The precision of mean of independent measurement results between independent dissolutions suggests that, for the majority of materials analysed, a minimum digested mass of 100 mg is recommended to mitigate the impact of small‐scale powder heterogeneity. Of the sixteen materials analysed, we therefore recommend for use as Tl reference materials the USGS materials BCR‐2, COQ‐1, GSP‐2 and STM‐1; CRPG materials AL‐I, AN‐G, FK‐N, ISH‐G, MDO‐G, Mica‐Fe, Mica‐Mg and UB‐N; NIST SRM 607 and OREAS14P.  相似文献   

Automated extraction of hydrographically corrected contours for the conterminous United States: the US Geological Survey US Topo product     

Samantha T. Arundel  Philip T. Thiem  Eric W. Constance 《制图学和地理信息科学》2018,45(1):31-55

The US Topo is a new generation of digital topographic maps delivered by the US Geological Survey (USGS). These maps include contours in the traditional 7.5-min quadrangle format. The process for producing digital elevation contours has evolved over several years, but automated production of contours for the US Topo product began in 2010. This process, which is quite complex yet fairly elegant, automatically chooses the proper USGS quadrangle, captures the corresponding 1/3 as grid points from the national elevation data set (3D Elevation Program), and adjusts elevation data to better fit water features from the National Hydrography Dataset. After additional processing, such as identifying and tagging depressions, constructing proper contours across double-line streams, and omitting contours from water bodies, contours are automatically produced for the quadrangle. The resulting contours are then compared to the contours on the original (legacy) topographic map sheets, or to the 10-m contours from the original map sheets. Where the elevation surface used to generate the contours has been derived from the previously published contours for a quadrangle, the generated contours match the legacy contours quite well. Where newer elevation sources, such as lidar, originate the elevation surface, generated contours may vary significantly from the previous cartographically produced contours due to more accurate representations of the surface, and less reliance on cartographic interpretation.  相似文献   

Crystallization and eruption ages of Breccia Museo (Campi Flegrei caldera,Italy) plutonic clasts and their relation to the Campanian ignimbrite     

Samantha?K.?Gebauer  Axel?K.?SchmittEmail author  Lucia?Pappalardo  Daniel?F.?Stockli  Oscar?M.?Lovera 《Contributions to Mineralogy and Petrology》2014,167(1):953

The Campi Flegrei volcanic district (Naples region, Italy) is a 12-km-wide, restless caldera system that has erupted at least six voluminous ignimbrites during the late Pleistocene, including the >300 km³ Campanian ignimbrite (CI) which originated from the largest known volcanic event of the Mediterranean region. The Breccia Museo (BM), a petrologically heterogeneous and stratigraphically complex volcanic deposit extending over 200 km² in close proximity to Campi Flegrei, has long remained contentious regarding its age and stratigraphic relation to the CI. Here, we present crystallization and eruption ages for BM plutonic ejecta clasts that were determined via uranium decay series and (U–Th)/He dating of zircon, respectively. Despite mineralogical and textural heterogeneity of these syenitic clasts, their U–Th zircon rim crystallization ages are indistinguishable with an average age of 49.7 ± 2.5 ka (2σ errors; mean square of weighted deviates MSWD = 1.2; n = 34). A subset of these crystals was used to obtain disequilibrium-corrected (U–Th)/He zircon ages which average 41.7 ± 1.8 ka (probability of fit P = 0.54; n = 15). This age closely overlaps with published CI ⁴⁰Ar/³⁹Ar eruption ages (40.6 ± 0.1 ka) after recalibration to recently revised flux monitor ages. Concordant eruption ages for BM and CI agree with previous chemostratigraphic and paleomagnetic correlations, suggesting their origin from the same eruption. However, they are at variance with recalibrated ⁴⁰Ar/³⁹Ar ages which have BM postdate CI by 3 ± 1 ka. BM syenites show similar geochemical and Sr–Nd isotopical features of pre-caldera rocks erupted between 58 and 46 ka, but are distinctive from subsequent caldera-forming magmas. Energy-constrained assimilation and fractional crystallization modeling of Nd–Sr isotopic data suggests that pre-caldera magmas formed a carapace of BM-type intrusions in a mid-crust magma chamber (≥8 km depth) shielding the younger CI magma from contamination by Hercynian basement wall rocks. An ~41–50 ka hiatus in crystallization ages implies rapid solidification of these pre-CI intrusions. This argues against protracted pre-eruptive storage of a large volume of CI magma at shallow crustal levels.  相似文献