排序方式： 共有8条查询结果，搜索用时 171 毫秒
1
1.
随着中国多颗偏振遥感器搭载发射,偏振遥感成为对地观测领域一个新的增长点以及研究热点。由于大气散射具有较强的偏振效应,大气与地表偏振信号的分离是偏振对地进行有效观测和应用的一个现实问题与难点问题。本文利用晴空中有规律的偏振分布以及大气偏振中性点的性质,对利用大气中性点的偏振效应进行地表—大气偏振信息分离的可行性进行了论证。通过对大气中性点在辐射传输过程性质的计算,得出Babinet大气中性点区域的偏振效应以及基于Babinet中性点区域进行偏振对地观测的基本方法,研究重点阐述了从航空遥感和航天遥感两个层面对如何将大气中性点应用于遥感观测进行了讨论。结果表明:(1)Babinet中性点相比于其他两个中性点,更适合于偏振遥感对地观测中地—气偏振参量分离;(2)航空遥感搭载偏振传感器在Babinet中性点区域进行地表探测可以消除大气偏振,突出地物偏振信息,有效进行地—气偏振参量分离;(3)在太阳同步轨道的卫星遥感影像上能够有效识别偏振中性点区域;研究成果有效分离高分辨率偏振遥感地物反演中的大气偏振耦合效应,实现地表偏振反射信息最大化,对于偏振遥感的大气校正以及定量化水平的提升具有实践意义。 相似文献
2.
Petrology and Geochemistry of Metabasalts from the 1.95 Ga Jormua Ophiolite, Northeastern Finland 总被引：9，自引：0，他引：9
The Jormua Ophiolite exposes a unique fragment of Red Seatypeoceanic crust formed in a setting related to continental break-up1950 Ma ago. Two distinct types of basalt are represented: the‘early dykes’ and the ‘main basalt suite’.‘Early dykes’ have fractionated (H) REE patterns,OIB-like trace element patterns, low Zr/Nb (6) and ENd(1.95Ga)–0.6, indicative of their derivation from an enrichedsource. The remaining dykes and all lavas belong to the second,E-MORB-like ‘main basalt suite’, which is characterizedby high mg-number and Cr contents, flat REE patterns, Zr/Nb= 6–17, chondritic Th/Ta and only moderately depletedisotopic signatures [END (1.95 Ga)+1.9]. Most ‘main suite’samples cannot be related solely by fractional crystallizationto a common parental magma. Rather, they represent distinctmelt fractions that underwent variable amounts of chromite +olivine plagioclase fractionation during ascent. A significantpart of the compositional diversity of the ‘main basaltsuite’ can be explained by mixing a depleted source witha relatively uniform proportion of an enriched component similarto that represented by the OIB-like ‘early dykes’.It is probable that during the latest stages of continentalrifting the OIB-type melts metasomatized the upper part of thedepleted asthenospheric mantle, which became the source of the‘main basalt suite’ soon after the old continentallithosphere was ruptured. The complete absence of any evidencefor a subduction-related component in the basalts implies thatJormua is not a back-are ophiolite.
*Fax: +358 0 462 205. e-mail: petri.peltonen{at}gsf.fi 相似文献
3.
4.
F. CHOPIN K. SCHULMANN P. ŠTÍPSKÁ J. E. MARTELAT P. PITRA O. LEXA B. PETRI 《Journal of Metamorphic Geology》2012,30(4):347-376
A microstructural and metamorphic study of a naturally deformed medium‐ to high‐pressure granitic orthogneiss (Orlica–?nie?nik dome, Bohemian Massif) provides evidence of behaviour of the felsic crust during progressive burial along a subduction‐type apparent thermal gradient (～10 °C km?1). The granitic orthogneisses develops three distinct microstructural types, as follows: type I – augen orthogneiss, type II – banded orthogneiss and type III – mylonitic orthogneiss, each representing an evolutionary stage of a progressively deformed granite. Type I orthogneiss is composed of partially recrystallized K‐feldspar porphyroclasts surrounded by wide fronts of myrmekite, fully recrystallized quartz aggregates and interconnected monomineralic layers of recrystallized plagioclase. Compositional layering in the type II orthogneiss is defined by plagioclase‐ and K‐feldspar‐rich layers, both of which show an increasing proportion of interstitial minerals, as well as the deformation of recrystallized myrmekite fronts. Type III orthogneiss shows relicts of quartz and K‐feldspar ribbons preserved in a fine‐grained polymineralic matrix. All three types have the same assemblage (quartz + plagioclase + K‐feldspar + muscovite + biotite + garnet + sphene ± ilmenite), but show systematic variations in the composition of muscovite and garnet from types I to III. This is consistent with the equilibration of the three types at different positions along a prograde P?T path ranging from <15 kbar and <700 °C (type I orthogneiss) to 19–20 kbar and >700 °C (types II and III orthogneisses). The deformation types thus do not represent evolutionary stages of a highly partitioned deformation at constant P?T conditions, but reflect progressive formation during the burial of the continental crust. The microstructures of the type I and type II orthogneisses result from the dislocation creep of quartz and K‐feldspar whereas a grain boundary sliding‐dominated diffusion creep regime is the characteristic of the type III orthogneiss. Strain weakening related to the transition from type I to type II microstructures was enhanced by the recrystallization of wide myrmekite fronts, and plagioclase and quartz, and further weakening and strain localization in type III orthogneiss occurred via grain boundary sliding‐enhanced diffusion creep. The potential role of incipient melting in strain localization is discussed. 相似文献
5.
6.
7.
Remote sensing of the impact of reindeer grazing on vegetation in northern Fennoscandia using SPOT XS data 总被引：1，自引：0，他引：1
Digital image analysis and SPOT XS satellite data recorded on 1 August 1991 were used to monitor vegetation in the border region between Enontekio municipality, Finland, and Kautokeino municipality, Norway. A supervised classification on the red wave length channel was undertaken using training areas for maximum likelihood classifier to produce seven spectral land cover classes. The classification revealed great differences in vegetation between Finland and Norway. The largest difference was the lack of Cladinalichens on the Finnish side of the border. The area on the Finnish side is used for grazing all year round, while the area on the Norwegian side is a winter range only. According to official data for the local reindeer population, the average annual grazing pressure (head/area/time) is higher on the Norwegian side of the reindeer fence. The Finnish grazing practice is believed to have a detrimental impact on the vegetation, and has lead to pasture land degradation. 相似文献
8.
HEIKKI SEPPÄ MATTI TIKKANEN PETRI SHEMEIKKA 《Boreas: An International Journal of Quaternary Research》2000,29(3):219-231
Lake isolation studies provide the most reliable method for reconstructing the shore displacement history of the areas affected by postglacial isostatic land uplift. Due to the slow uplift rate and the presence of numerous lakes, the Finnish south coast is one of the key areas for investigating the Litorina transgression and subsequent shore displacement history of the Baltic. To reconstruct the relative sea-level dynamics during the late Holocene, three small lakes from the critical altitudes were analysed concerning their diatom, sulphate-sulphur, and sodium stratigraphies and loss-on-ignition values. Comparisons of the records indicate that the availability of nutrients significantly influenced the diatom-floristic patterns during the lake isolation. In particular, the mass occurrence of Fragilaria spp. seems to be associated with high values of sulphate-sulphur and sodium during and after isolation. On the basis of the new and old data, a shore displacement curve for the 30 m Litorina isobase is compiled. This indicates that since the clear Litorina transgression at 7500-6500 14C BP, no transgressions have taken place but that the shore displacement in the area has been a stable process. The occurrence of a number of raised shore formations between the altitude of the major Litorina shore and the present sea level in south Finland can be attributed to the erosion of soft soil layers by the high-energy wave action on the exposed shore sections. 相似文献
1