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671.
高光谱影像数据预处理是构建高效的影像数据库以及实现地理目标成分信息反演与地理目标识别的基础。本文从反射率演算、光谱微分技术以及高光谱影像数据的降维处理等三个方面对高光谱影像数据预处理进行了研究。实现了基于高光谱影像的反射率反演算法,针对高光谱遥感数据影像分辨率比较低的现状,提出了直方图均衡化、色调平衡、对比度调整等影像处理算法,并给出了实验结果。 相似文献
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Tilt corrections over complex terrain and their implication for CO<Subscript>2</Subscript> transport
Jielun Sun 《Boundary-Layer Meteorology》2007,124(2):143-159
Observational data from sonic anemometers are commonly rotated from sonic to streamline coordinates, a procedure that is called
tilt correction. Tilt corrections are often used to post-process air velocity data collected from sonic anemometers to allow
objective interpretation of air flow data relative to the Earth. Since streamline coordinates depend on dynamical characteristics
of the flow, the tilt correction depends not only on temporal and spatial variations of the flow, but also on local circulations.
We found that ensemble- averaged slope flows are approximately parallel to the terrain slope close to the ground within the
canopy layer, but not above, due to the influence of the diurnal variation of local vertical circulations. As a result, the
diurnal variation of the observed vertical velocity in streamline coordinates at 21.5 m above the ground over 11-m tall forest
canopies can be opposite to that calculated from the continuity equation. To estimate CO2 transport over sloping terrain, a workable reference coordinate system is needed such that multiple sonic anemometers have
a common reference relative to the Earth. Streamline coordinate systems can be the choice of the common reference coordinate
system only if flow, at least ensemble-averaged flow, is parallel to terrain slopes. The choice of the reference coordinate
system and its implication in investigation of CO2 transport are discussed.
The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
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Summary A novel multi-timescale analysis method, Empirical Mode Decomposition (EMD), is used to diagnose the variation of the annual
mean temperature data of the global, Northern Hemisphere (NH) and China from 1881 to 2002. The results show that: (1) Temperature
can be completely decomposed into four timescales quasi-periodic oscillations including an ENSO-like mode, a 6–8-year signal,
a 20-year signal and a 60-year signal, as well as a trend. With each contributing ration of the quasi-periodicity discussed,
the trend and the 60-year timescale oscillation of temperature variation are the most prominent. (2) It has been noticed that
whether on century-scale or 60-year scales, the global temperature tends to descend in the coming 20 years. (3) On quasi 60-year
timescale, temperature abrupt changes in China precede those in the global and NH, which provides a denotation for global
climate changes. Signs also show a drop in temperature in China on century scale in the next 20 years. (4) The dominant contribution
of CO2 concentration to global temperature variation is the trend. However, its influence weight on global temperature variation
accounts for no more than 40.19%, smaller than those of the natural climate changes on the rest four timescales. Despite the
increasing trend in atmospheric CO2 concentration, the patterns of 20-year and 60-year oscillation of global temperature are all in falling. Therefore, if CO2 concentration remains constant at present, the CO2 greenhouse effect will be deficient in counterchecking the natural cooling of global climate in the following 20 years. Even
though the CO2 greenhouse effect on global climate change is unsuspicious, it could have been excessively exaggerated. It is high time to
re-consider the trend of global climate changes. 相似文献
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Summary The cut-off lows (COLs) during the period from June to August 1998 leading to the record flood in Northeast Asia, especially
in Northeast China, has been investigated in this paper. The results are as follows: the blocking highs benefited significantly
the formation and maintenance of COLs over Northeast China; an obvious frontogenesis zone existed in Northeast China and it
implies that baroclinity played an important role in the initiation of COLs, especially in middle and upper troposphere; the
maxima of the potential vorticity anomaly were located in the upper troposphere, then extended downwards to the middle and
the lower troposphere. The pronounced interaction between systems in upper-middle and low troposphere can be revealed; the
moisture supply was from South China, and even from East China Sea and South China Sea. The strong southerly current transported
very rich moisture to Northeast China. The maximum of the convergence of moisture flux was below 850 hPa. Obvious interaction
between the middle and lower latitude systems was found in the study. Also, the summer monsoon showed significant impacts
on the sustained heavy rainfalls related with the COLs over Northeast China; the upward motion could be caused by the lifting
of the large scale dynamic forcing and there was no obvious releasing of latent heating in the upper-middle troposphere. The
cold dome in the COLs was quite different both from the warm core in tropical cyclone and from the weaker warm core in Meiyu
(Baiu) front low. The calculation of vorticity budget shows that both the horizontal advection term and horizontal divergence
term contributed importantly to the maintenance and the strengthening of positive relative vorticity. Finally, the complex
dynamical characteristics regarding the COLs are discussed and further investigation is proposed. 相似文献
678.
Seasonal Transition Features of Large-Scale Moisture Transport in the Asian-Australian Monsoon Region 总被引:18,自引:0,他引:18
Using NCEP/NCAR reanalysis data for the period of 1957-2001, the climatological seasonal transition features of large-scale vertically integrated moisture transport (VIMT) in the Asian-Australian monsoon region are investigated in this paper. The basic features of the seasonal transition of VIMT from winter to summer are the establishment of the summertime "great moisture river" pattern (named the GMR pattern) and its eastward expansion, associated with a series of climatological events which occurred in some "key periods", which include the occurrence of the notable southerly VIMT over the Indochina Peninsula in mid March, the activity of the low VIMT vortex around Sri Lanka in late April, and the onset of the South China Sea summer monsoon in mid May, among others. However, during the transition from summer to winter, the characteristics are mainly exhibited by the establishment of the easterly VIMT belt located in the tropical area, accompanied by some events occurring in "key periods". Further analyses disclose a great difference between the Indian and East Asian monsoon regions when viewed from the meridional migration of the westerly VIMT during the seasonal change process, according to which the Asian monsoon region can be easily divided into two parts along the western side of the Indochina Peninsula and it may also denote different formation mechanisms between the two regions. 相似文献
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