消除CCD天光背景的一种组合式分割方法     

蔡志武  王洪彦 《测绘学院学报》2003,20(1):26-28

基于迭代阈值法和统计模型提出了一种新的组合式分割方法，该方法精确地描述了天光背景的分布情况，既能够精确确定图像分割的最优阈值，有效地消除天光背景的影响，又可以精确地估计出天光的平均强度，有利于天体亮度的精确计算及暗星的探测。  相似文献   

晴空或少云状况下紫外辐射强度及指数预报模式   总被引：4，自引：0，他引：4  

傅炳珊  车少静  陈渭民  马翠平 《南京气象学院学报》2002,25(3):321-327

在大气辐射传输理论的基础上，利用中分辨率大气辐射传输系统，应用可测得的实际大气物理参数，建立睛空或少云天气状况下石家庄市紫外波段（280-400nm)辐射强度及指数预报模式，考虑了臭氧的两个吸收带。晴空条件下的散射主要考虑了分子和气溶胶的多次散射，少云时还考虑了云对紫外辐射的影响。其中多次散射的计算采用子离散坐标法。且对由于臭氧实时资料的短缺造成的误差进行了系统订正，并将订正结果与实况资料进行了对比。结果表明，由模式客观预报紫外辐射强度是可行的。  相似文献   

华东地区大气臭氧总量的变化特点          下载免费PDF全文

洪盛茂 《气象》1997,23(5):44-46

分析了１９９３年１２月至１９９４年１１月的大气臭氧总量资料并与同纬度全球平均值进行比较，分析了大气臭氧总量的年变化、日变化和季节变化。结果表明，臭氧总量的年变化中有双峰特征，它的日变化则以中午时较高，早晚较低；季节变化以春季高，冬季低，与大气透明度的关系较为密切  相似文献   

应用二向性反射分布函数进行反照率的精确计算和邻近象元效应校正(英文)     

ＣｈｒｉｓｔｏｐｈＣ．Ｂｏｒｅｌ  ＳｉｅｇｆｒｉｅｄＡ．Ｗ．Ｇｅｒｓｔｌ 《遥感学报》1997,(Z1)

该文讨论二向性反射分布函数（ＢＲＤＦ）在遥感领域中两方面的应用：（１）晴天大气层顶部的反照率的确定，（２）二向性反射分布函数对邻近象元点扩散函数和大气订正的影响。大气层顶部的光谱反照率是从多角度成象光谱辐射计（ＭＩＳＲ）提取的重要参数，其精度主要取决于我们对不同情况表面建立更好的ＢＲＤＦ模型。该文论述一种与９个ＭＩＳＲ二向性反射观测值相匹配的半经验函数的算法，并可进而通过数值积分产生４个光谱波段的晴天大气层顶部的光谱反照率。结果显示反照率的绝对精度对可见光波段可高于１％，对近红外波段可高于２％。采用一种简化的辐射通量模型，我们的工作显示邻近象元点扩散函数（ＰＳＦ）的形状取决于下垫面表面的ＢＲＤＦ。在给定与中心象元的偏移（ｘ，ｙ）的条件下邻近象元的点扩散函数，由和沿观察方向的散射相函数的传输加权的乘积的积分给定。  相似文献   

Marine Layer Stratus Study     

Leonard A. Wells 《Pure and Applied Geophysics》2007,164(6-7):1397-1421

The intent of this study is to develop a better understanding of the behavior of late spring through early fall marine layer stratus and fog at Vandenberg Air Force Base, which accounts for a majority of aviation forecasting difficulties. The main objective was to use Leipper (1995) study as a starting point to evaluate synoptic and mesoscale processes involved, and identify specific meteorological parameters that affected the behavior of marine layer stratus and fog. After identifying those parameters, the study evaluates how well the various weather models forecast them. The main conclusion of this study is that weak upper-air dynamic features work with boundary layer motions to influence marine layer behavior. It highlights the importance of correctly forecasting the surface temperature by showing how it ties directly to the wind field. That wind field, modified by the local terrain, establishes the low-level convergence and divergence pattern and the resulting marine layer cloud thicknesses and visibilities.  相似文献   

Radiative characteristics in a Japanese forested drainage basin during snowmelt     

H. Nakabayashi  N. Ishikawa  Y. Kodama 《水文研究》1999,13(2):157-167

Radiative characteristics in a forested drainage basin during the snowmelt season were examined in order to better understand and predict snowmelt runoff in the basin. A method for estimating net radiation in a forest (R_nf) was presented using the total sky view factor (P) and the sun path sky view factor (Q). Solar radiation, albedo, atmospheric radiation and air temperature observed at an open site were also required. The total and the sun path sky view factors were determined from all‐sky photographs. Q was expressed as a linear function of P for 0·15<P<0·86 regardless of forest type. For P<0·15, Q was set to zero, and for P>0·86, Q was equal to unity. The short‐wave radiation budget at the forest floor (S_nf) increased with P, whereas the long‐wave radiation budget (L_nf) decreased with P. R_nf increased with P for 0·15<P<0·86, and changed little with P for P<0·15 and P>0·86, as the increase in S_nf was offset by the decrease in L_nf . The forest effect on R_nf was diminished under cloudy or high albedo conditions, because S_nf was easily offset by L_nf . This estimation method was extended to the whole basin, and R_nf was obtained over a watershed covered by trees. At the beginning of the snowmelt season when the albedo remained high, the forest effect became null because the decrease in S_nf was balanced by the increase in L_nf . As the albedo gradually lowered with the advance of the snowmelt season, the decrease in S_nf owing to forest covers exceeded the increase in L_nf , and the forest effect to decrease R_nf became evident. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

Strategies for managing reservoir sedimentation   总被引：2，自引：1，他引：1  

Zhao-yin WANG  Chunhong HU Prof.  State Key Lab of Hydroscience  Engineering  Tsinghua University  Beijing  China. Prof.  Secretary General of International Research  Training Center on Erosion  Sedimentation  Beijing  China  Vice President of China Institute of Water Resources  Hydropower Research  No. A-  Fuxing Rd  Beijing  China. 《国际泥沙研究》2009,24(4):369-384

Sediment deposition in reservoirs has caused the loss of 66% of the reservoir capacity in China. The main sedimentation control strategies are： 1） storing the clear water and releasing the turbid water; 2） releasing turbidity currents; 3） Draw-down flushing and empty flushing; and 4） dredging, The paper summarizes these strategies with examples. Sediment transport in many Chinese rivers occurs mostly during the 2-4 month flood season, that is, 80-90% of the annual sediment load is transported with 50-60% of the annual runoff. By storing the clear water after the flood season and releasing the turbid water during the flood season, less sediment deposits in the reservoir while the reservoir is still able to store enough water for power generation in the low flow season. The Three Gorges and Sanmenxia reservoirs apply this strategy and control sedimentation effectively. Turbidity currents have become the main sedimentation control strategy for the Xiaolangdi Reservoir. Empty flushing involves reservoir draw-down to temporarily establish riverine flow along the impound reach, flushing the eroded sediment through the outlets. Case studies with the Hengshan Reservoir and Zhuwo Reservoir are presented. Jet dredgers have been used to agitate the reservoir deposit so that the deposit is released from the reservoir with currents. The sediment releasing efficiency is 30-100% for storing the clear and releasing the turbid; 6-40 % for turbidity current; and 2,400-5,500% for empty flushing. Empty flushing causes high ecological stress on the ecosystem to the downstream reaches. Storing the clear and releasing the turbid is the best strategy to control reservoir sedimentation while achieving hydro-power benefit and maintain ecological stability.  相似文献   

Modeling the land surface reflectance for optical remote sensing data in rugged terrain   总被引：1，自引：0，他引：1  

JianGuang Wen  QinHuo Liu  Qing Xiao  Qiang Liu  XiaoWen Li 《中国科学D辑(英文版)》2008,51(8):1169-1178

A model for topographic correction and land surface reflectance estimation for optical remote sensing data in rugged terrian is presented.Considering a directional-directional reflectance that is used for direct solar irradiance correction and a hemispheric-directional reflectance that is used for atmospheric diffuse irradiance and terrain background reflected irradiance correction respectively,the directional reflectance-based model for topographic effects removing and land surface reflectance calculation is developed by deducing the directional reflectance with topographic effects and using a radiative transfer model.A canopy reflectance simulated by GOMS model and Landsat/TM raw data covering Jiangxi rugged area were taken to validate the performance of the model presented in the paper.The validation results show that the model presented here has a remarkable ability to correct topography and estimate land surface reflectance and also provides a technique method for sequently quantitative remote sensing application in terrain area.  相似文献   

Cloudy Sky Conditions Promote Net Ecosystem CO2 Exchange in a Subtropical Coniferous Plantation across Seasons     

HAN Jiayin  YE Shu  GUO Chuying  ZHANG Leiming  LI Shenggong  WANG Huimin 《资源与生态学报(英文版)》2019,10(2):137-146

Dynamic changes in solar radiation have an important influence on ecosystem carbon sequestration, but the effects of changes caused by sky conditions on net ecosystem CO₂ exchange (NEE) are unclear. This study analyzed the effects of sunny, cloudy, and overcast sky conditions on NEE using carbon flux and meteorological data for a subtropical coniferous plantation in 2012. Based on one-year data, we found no seasonal variation in the light response curve under various sky conditions. Compared with sunny sky conditions, the apparent quantum yield (α) and potential photosynthetic rate at a light intensity of 150 and 750 W m^-2 (P₁₅₀ and P₇₅₀) under cloudy sky conditions increased by an average of 82.3%, 217.7%, and 22.5%; α and P₁₅₀ under overcast sky conditions increased by 118.5% and 301% on average. Moderate radiation conditions were more favorable for maximum NEE, while low radiation conditions inhibited NEE. In most cases, when the sunny NEE was used as a baseline for comparison, the relative change in NEE (%NEE) was positive under cloudy sky conditions and negative under overcast sky conditions. The average maximal %NEE under cloudy sky conditions was 42.4% in spring, 34.1% in summer, 1.6% in autumn and -87.3% in winter. This study indicates that cloudy sky conditions promote photosynthetic rates and NEE in subtropical coniferous plantations.  相似文献   

北京天文台兴隆观测站夜天光光谱证认     

姜晓军  姜晓军  徐达维  胡景耀  胡景耀 《中国天文和天体物理学报》1999,(2)

介绍了夜天光光谱的观测方法,给出了北京天文台兴隆观测站５３０ｎｍ－８２０ｎｍ的夜天光发射光谱,并对它们进行了证认,测定了大气辉光线的夜变化;光谱中城市灯光线ＮａＩ和ＨｇＩ均较弱,表明兴隆站目前的光污染尚不严重．  相似文献