数字水印技术与算法实现

综述了数字水印技术的起源、概念、特点和应用；提出了数字水印处理技术的基本框架；列出了一些主要的基于图像的水印嵌入算法和水印检测算法；并展望了水印处理技术的未来发展趋势；最后给出了一种基于DCT变换的水印嵌入与检测算法。     

基于Skyline的扬州市三维可视化系统的设计与应用

随着城市化进程的进一步加快,政府对城市统筹规划技术的要求日益增高。现代城市的规划设计更加需要科学的系统进行辅助决策。本文以扬州市三维可视化系统的成功建设,介绍了三维数字城市系统建设中的Skyline结合3Dmax快速建模技术,论述了Skyline三维平台建设虚拟城市的方法和策略,并利用其提供的应用程序接口进行了二次功能开发,一定程度上为数字城市规划建设提供技术支持与参考。     

不同类型草地挥发性有机物排放特征的研究

2003年9月,对内蒙古草原不同类型草地挥发性有机物(VOC)的排放、太阳辐射、气象参数等进行观测,结果表明,固定和新的羊草样地、封育样地、不同程度放牧样地异戊二烯、α蒎烯、β蒎烯、柠檬烯、蒈烯的排放均有明显的日变化规律,并与可见光辐射以及温度有较好的一致性.羊草样地、封育样地、过度放牧、适度放牧样地异戊二烯排放的最大值分别为139.5、25.9、132.3、107.1(单位:μg·m-2·h-1,以碳计).多数情况下,异戊二烯排放通量的测定结果为羊草样地高于封育样地、过度放牧样地高于适度放牧样地.不同程度放牧样地α蒎烯、β蒎烯、柠檬烯、蒈烯等的排放具有明显差别,一般是过度放牧草地高于适度放牧草地.剪草增大了绝大部分VOC组分的排放、以及过度和适度放牧草地VOC的排放,剪草可以造成过度和适度放牧草地异戊二烯排放在中午前后的增加.剪草后,过度放牧草地异戊二烯、α蒎烯、β蒎烯、柠檬烯、蒈烯等的排放通量均远大于适度放牧草地的相应值.土壤异戊二烯、α蒎烯、β蒎烯等的排放很小,分别占相近可见光辐射和温度条件下固定羊草样地排放的0.2%、0、3.0%.     

BDS卫星失效对区域定位精度的影响评估

基于STK软件实现了2016-09 BDS系统星座结构的仿真,并选取可见卫星数、DOP值、系统可用性作为评估BDS卫星星座设计结构的指标,分析单颗与全部倾斜轨道卫星（IGSO）、地球静止轨道卫星（GEO）失效后对我国大陆地区BDS系统可用性的影响。结果表明,IGSO4卫星与GEO5卫星失效后对BDS在区域的定位性能影响较大,失效后的GDOP值分别为1.98、2.16。取BDS卫星正常运行时区域平均GDOP最大值(S=2.60)作为系统可用性阈值时,系统可用性分别降低了1.79%、32.63%;阈值取2S(5.20)、3S(7.80)、4S(10.40)、5S(13.00)时,系统可用性均可达100.00%。GEO整体失效后BDS系统在高精度定位中仍部分可用,而IGSO整体失效后BDS系统可用性受到大幅度限制。因此,增加在轨备份卫星时需重点考虑GEO5、IGSO4,并适当增加IGSO卫星的数目。     

Assessment of the Uncertainties in the NO2 and O3 Measurements by Visible Spectrometers

The column amounts of nitrogen dioxide (NO2) and ozone (O3) were measured using a visible spectrometer based on the twilight zenith-sky technique at two observatories located at similar latitudes in the northern part of Japan separated by a distance of 150 km. The measurements began in April 1991 at the Moshiri Observatory (44.4°N, 142.3°E) and in April 1994 at the Rikubetsu Observatory (43.5°N, 143.8°E). Since weather conditions and the possible influence from tropospheric pollution were not always identical at these two observatories, the overall accuracy of the measurements was studied comparing these data sets. The first year data obtained at a solar zenith angle of 90 degrees indicated that the NO2 slant column values at sunrise and sunset agreed within 0.36 and 0.54 × 1016 cm-2, respectively, corresponding to 5 % (June) and to 12 % (December) of the columns. The O3 values agreed within 0.76 × 1019 cm-2, corresponding to 4 % (March) 6 % (August) of the columns, although a part of the difference was systematic. The O3 column amounts were also compared to those obtained by the Dobson spectrometer at Sapporo (43.5°N, 143.8°E), whose latitude is similar to these observatories. When an air mass factor of 17.5 was used, the two-year Moshiri vertical column values agreed with the Dobson direct sun values to within 15 Dobson Units, or 3 6 % of the column. The difference between the two values was found to be due partly to the change in the air mass factor caused by seasonal and day-to-day changes in the shape of the O3 vertical profiles. These results confirm the reliability of the NO2 and O3 measurements by visible spectrometers at these sites for the Network for the Detection of Stratospheric Change (NDSC).     

Upper Limit of Iodine Oxide in the Lower Stratosphere

It has been suggested that iodine oxides, IOx, could play a significant role in the ozone destruction in the lower stratosphere. To investigate this suggestion, spectra from nine SAOZ uv-visible spectrometer balloon flights were examined for the IO absorption signature between 405 and 450 nm. IO was not detected, either at mid- or high latitude, in the morning or the evening, in summer or winter. An upper limit of 0.2 parts per trillion by volume (pptv) at 20 km and 0.1 pptv at 15 km at the 95% confidence level (2), was derived from the best measurements at 90° SZA at sunset and sunrise. Since a photochemical model shows that 70% of inorganic iodine should be in the form IO at that time, it is concluded that unless iodine chemistry is different from that assumed at the moment, the role of iodine in stratospheric ozone depletion is small.     

低轨卫星增强北斗三号导航星座性能分析

针对低轨卫星星座有待合理化设计的问题,深入研究了低轨卫星星座增强北斗三号系统定位性能。分析轨道高度、轨道倾角、星座构型对星座覆盖性能的影响,仿真北斗三号、GPS和3种不同类型的低轨星座,研究各低轨星座与北斗三号、GPS的组合系统在所选7个测站以及全球范围内的可见卫星数和PDOP值分布。结果表明低轨卫星对北斗三号的增强效果主要与低轨卫星数目有关,且不同轨道倾角的组合低轨星座有利于均衡系统在全球范围内的可见卫星数与PDOP值分布。低轨卫星有望通过改善卫星观测几何构型提高北斗三号系统的定位性能,且增强效果与低轨星座构型密切相关。     

缝洞型油藏大尺度可视化水驱油物理模拟实验及机理

缝洞型碳酸盐岩油藏由于其缝洞组合关系的复杂性,使得储层流体的渗流规律有别于常规油藏。根据某油田奥陶系缝洞型碳酸盐岩的实际情况设计制作了大尺度可视化物理模型,并按照现场实际设计了二注三采的实验井网及注采方案,以应用物理模拟实验来研究缝洞型碳酸盐岩油藏的开发特征及油井生产规律。结合实验结果,利用J.Cruz-Hernández建立的数学模型对生产数据进行拟合,以研究缝洞型碳酸盐岩油藏中流体的渗流机理,J.Cruz-Hernández数学模型中的空间系数和流动速度对采收率影响较大,提出模型的改进应考虑重力分异作用、溶洞比例等影响因素。     

基于离散小波变换的数字水印技术

提出了一种基于小波分析的简单有效的数字水印嵌入和盲检测的算法。先将嵌入的水印信息加密，然后将加密后的水印信息嵌到相应DWT系数的有效嵌入位中，并使用适当的保真技术，减小图像因嵌入水印引起的失真。通过实验验证，该算法在对嵌入水印后的图像进行有损压缩、剪切、污染、添加各种噪声等处理后，提取出的水印仍表现出了较好的鲁棒性。