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241.
242.
Peter Scull Greg Okin Oliver A. Chadwick Janet Franklin 《The Professional geographer》2005,57(3):423-437
Surface soil texture controls many important ecological, hydrological, and geomorphic processes in arid regions and is therefore important from a land‐management perspective. Soil survey efforts have traditionally fulfilled this need, but they are constrained by the size, remoteness, and inaccessibility of many arid regions, which renders simple field measurements prohibitively expensive. This article compares several different predictive soil‐mapping techniques with a sparse data set in order to develop surficial soil texture maps. Our results suggest that data collected at the landscape scale can be used as input to predictive soil‐mapping techniques to create maps of soil texture at higher fidelity and a fraction of the cost than would be required using traditional methods. 相似文献
243.
Numerical Simulation Study on the Scientific and Methodological Aspects of the Brazilian Proposal
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1. IntroductionObservations of surface air temperature indicatethat a significant global average warming has occurredduring the 20th century. The Intergovernmental Panelon Climate Change (IPCC, 2001) concludes that thereis new and stronger evidence that man has influencedthe climate. International negotiations have led to afirst step in combating climate change with the UnitedNations Framework Convention on Climate Change(UNFCCC) and the Kyoto Protocol, but further stepsare needed in … 相似文献
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245.
Automated digital photogrammetry was used to produce digital elevation models of experimental model landscapes under controlled laboratory conditions as part of a series of rainfall erosion experiments looking at the evolution of landforms in response to erosion. The method allowed the elevations of the experimental landscapes to be studied in great detail on a regular grid digital terrain map with relatively very little effort. Digital photogrammetry produced elevation data at a resolution of 6 mm with a standard deviation of 2·0 mm over an experimental catchment relief of approximately 200 mm; this resolution is considerably better than that achievable by conventional manual photogrammetry. The density of grid points was sufficiently high that small‐scale details such as knickpoints developing in channels were represented. The method can facilitate the study of both experimental and natural landscapes in great detail. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
246.
The U/Pb dating of ophiolite and arc complexes in the Caledonides of SW Norway has demonstrated that these spatially associated
rocks are also closely related in time. A sequence of tholeiitic island arc volcanics, and an unconformably overlying sequence
of calc-alkaline volcanics have been dated as 494 ± 2 Ma (2σ) and 473 ± 2 Ma respectively. Ophiolitic crust formed both prior
to, and during the first 10 Ma after the tholeiitic island arc volcanism. Boninitic and island arc tholeiitic dyke swarms
intruded the ophiolites soon after they formed and represent a second phase of spreading-related magmatism in the ca 20 Ma
period that separated the tholeiitic and the calc-alkaline island arc volcanism. The magmatism ended with the formation of
alkaline, ocean island basalt (OIB)-like magmas. Quartz dioritic and S-type granitic plutons, dated to 479 ± 5 Ma and 474 +3/−2 Ma
respectively, intruded into the base of the arc crust during and subsequent to the boninitic magmatism, and at the time when
calc-alkaline volcanic centres developed. The quartz dioritic and the granitic rocks contain inherited zircons of Precambrian
age which prove the involvement of a continental source. This together with the geology of the terrain and the geochemistry
of these plutons suggests that the granitic magmas were partly derived from subducted clastic sediments. The Sr and Nd isotope
systematics indicate that the same continental source was a component in the boninitic and the calc-alkaline magmas. While
the calc-alkaline magmas may have gained this continental component at a crustal level by assimilation, both geology and isotope
systematics suggest that the continental component in the boninitic rocks was introduced by source contamination – possibly
by a direct interaction between the mantle source and the S-type granitic magmas. A modified mid ocean ridge basalt-like mantle
source was the principal source during the earliest and the main crust forming stage. This source became replaced by an OIB-like
source during the later stages in the evolution of this ancient arc.
Received: 27 June 1994 / Accepted: 16 September 1996 相似文献
247.
Understanding the nature and relative importance of various drivers of change is crucial for sustainable management of natural resources and in prioritizing management efforts, allocating limited resources, and understanding cumulative effects. For this article, we employed structured an expert judgments approach to identify, characterize, and assess the relative importance of the key biophysical and socioeconomic drivers of change within the Volta River Basin, West Africa. Precipitation variability, water availability, land use change, drought events, and population growth were perceived as most important, while biodiversity loss, social conflicts, pest and disease occurrence, urbanization, and pollution were viewed as less critical. A majority of these drivers were characterized as “slow” acting processes as compared to rapidly changing drivers. Intra- and interexpert groups agreement were found to be significant and convergent, indicating the reliability of the results. The implications of these results for sustainable water resources management and agricultural production are discussed. 相似文献
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249.
Hiroshi Murakami Kosei Sasaoka Kohtaro Hosoda Hajime Fukushima Mitsuhiro Toratani Robert Frouin B. Greg Mitchell Mati Kahru Pierre-Yves Deschamps Dennis Clark Stephanie Flora Motoaki Kishino Sei-Ichi Saitoh Ichio Asanuma Akihiko Tanaka Hiroaki Sasaki Katsumi Yokouchi Yoko Kiyomoto Hiroaki Saito Cécile Dupouy Absornsuda Siripong Satsuki Matsumura Joji Ishizaka 《Journal of Oceanography》2006,62(3):373-393
The Global Imager (GLI) aboard the Advanced Earth Observing Satellite-II (ADEOS-II) made global observations from 2 April
2003 to 24 October 2003. In cooperation with several institutes and scientists, we obtained quality controlled match-ups between
GLI products and in-situ data, 116 for chlorophyll-a concentration (CHLA), 249 for normalized water-leaving radiance (nLw) at 443 nm, and 201 for
aerosol optical thickness at 865 nm (Tau_865) and Angstrom exponent between 520 and 865 nm (Angstrom). We evaluated the GLI
ocean color products and investigated the causes of errors using the match-ups. The median absolute percentage differences
(MedPD) between GLI and in-situ data were 14.1–35.7% for nLws at 380–565 nm, 52.5–74.8% nLws at 625–680 nm, 47.6% for Tau_865, 46.2% for Angstrom, and 46.6%
for CHLA, values that are comparable to the ocean-color products of other sensors. We found that some errors in GLI products
are correlated with observational conditions; nLw values were underestimated when nLw at 680 nm was high, CHLA was underestimated
in absorptive aerosol conditions, and Tau_865 was overestimated in sunglint regions. The error correlations indicate that
we need to improve the retrievals of the optical properties of absorptive aerosols and seawater and sea surface reflection
for further applications, including coastal monitoring and the combined use of products from multiple sensors. 相似文献
250.