Modelling the optical turbulence boiling and its effect on finite-exposure differential image motion

It is usually accepted that whenever dealing with astronomical observation through the atmosphere, the optical turbulence temporal evolution can be sufficiently described with the so-called frozen turbulence hypothesis. In this model, turbulence is supposed to be equivalent to a series of solid phase screens that slide horizontally in front of the observation field of view. Experimental evidence shows, however, that an additional physical process must be taken into account when describing the temporal behaviour of the optical turbulence. In fact, while translating above the observer, turbulence undergoes a proper temporal evolution and affects differently the astronomical and, more specifically, the astrometric observations. The proper temporal evolution of the turbulence-induced optical turbulence observable quantities is here called the optical turbulence boiling. We are proposing through this paper a theoretical approach to the modelling of the optical turbulence temporal evolution when the turbulent layer horizontal translation and the optical turbulence boiling are both involved. The model we propose, as a working hypothesis though, has a direct relevance to differential astrometry because of its explicit dependence upon the optical turbulence temporal evolution. It can also be generalized to other techniques of high angular resolution astronomical observation through the atmospheric turbulence.     

Effect of Contour Intervals and Grid Cell Size on the Accuracy of DEMs and Slope Derivatives

Digital Elevation Models (DEMs) are indispensable tools in many environmental and natural resource applications. DEMs are frequently derived from contour lines. The accuracy of such DEMs depends on different factors. This research investigates the effect of sampling density used to derive contours, vertical interval between contours (spacing), grid cell size of the DEM (resolution), terrain complexity, and spatial filtering on the accuracy of the DEM and the slope derivative. The study indicated different alternatives to achieve an acceptable accuracy depending on the contour interval, the DEM resolution and the complexity of the terrain. The effect of these factors on the accuracy of the DEM and the slope derivative was quantified using models that determine the level of accuracy (RMSE). The implementation of the models will guide users to select the best combination to improve the results in areas with similar topography. For areas with variable terrain complexity, the suggestion is to generate DEMs and slope at a suitable resolution for each terrain separately and then to merge the results to produce one final layer for the whole area. This will provide accurate estimates of elevation and slope, and subsequently improve the analyses that rely on these digital derivatives.     

X-CT机空间分辨率测试规范的探讨

空间分辨率有四种测试方法：分辨成排圆孔模型测极限分辨率;分辨成排条形模型测极限分辨率;扫描针模计算ＭＴＦ曲线;扫描条形模型计算ＭＴＦ曲线。前二种方法直观、简单,但模体重、体积大,且测量结果有一定主观因素,这两种方法用于日常质量控制为宜。第三种方法能得到完整的ＭＴＦ曲线,但计算过程复杂,本文推荐使用最后一种方法,并简述其原理,认为该方法测量ＭＴＦ曲线简便易行。     

DETERMINATION OF GASEOUS COMPOSITION IN THE MIDDLE ATMOSPHERE BY USING HIGH SPECTRAL RESOLUTION METHODS

One of the crucial problems in study on the middle atmosphere is to determine theconcentration and distribution of some trace gases.In this aspect,sounding methods with highspectral resolution have been developed by many scientists.Some major trace gases and theirspectral characteristics,space-borne limb method for determination of trace gases in the middleatmosphere are introduced,requirements for used methods and instruments,development andchallenge encountered by sounding of trace gases with high spectral resolution are discussed in thispaper.     

地震势能剖面

地质体在应力场的作用下发生弹性形变,从而具有应变位能（势能）。应用应变位能公式,可以将位或位移转化为势能,用势能剖面代替常规地震剖面。由于势能转换能拓宽地震信号的有效频谱,具有高通滤波性质,同时又不损害低频信号,所以,同常规地震剖面相比,势能剖面在保持信噪比的前提下,有更高的纵、横向分辨率。通过势能转换的理论分析及合成数据和实际数据的势能转换处理,本文系统地研究了势能转化问题和实现方法,从而证明势能转换确实是行之有效的高分辨率地震处理方法,可用于实际地震资料的处理。     

大气质量综合航空测量系统简介

在全球范围内,大气污染日趋严重,已影响到人类的生存和发展。近几年高光谱遥感技术应用,可准确探明地球地貌,识别军事目标,区分岩性和植被。而高光谱数据和大气质量有关,即受大气污染和大气含尘量的影响。为此,我国境内大气质量监测等项工作势在必行。本文列出了评价大气质量的几个主要参数、所需设备的基本情况,并在此基础上进行了系统设计,讨论了解决在硬件设计和软件编程过程中所遇到的问题等。     

第四纪孢粉分析的时间序列与空间模型

论述了第四纪孢粉时间序列和孢粉空间模型在不同尺度上的时空代表性,同时介绍了一些相关的研究方法和主要成果。利用数理统计方法来定量恢复古气候已成为目前第四纪孢粉时间序列研究的一个发展趋势。各种尺度的第四纪孢粉空间模型图可以反映植被对第四纪气候变化的响应。根据孢粉数据与气候变量之间的函数关系还可换算成古气候图。此外,在全球气候模拟和植被模拟中,孢粉数据成为必不可少的诊断工具。     

No peace for the forest: Rapid,widespread land changes in the Andes-Amazon region following the Colombian civil war

Negative environmental impacts of violent conflict have been observed worldwide. Whether or not active global conflicts are declining in number remains hotly debated, the number of countries entering post-conflict periods is on the rise, and the impact of this transition on land cover changes remains poorly understood. In Colombia, though large-scale armed conflict has concluded, the post-conflict period represents an ongoing threat to forest conservation, putting at risk commitments to meet global conservation goals and even those stipulated in the peace accord. This paper aims to assess land cover change associated with the Colombian conflict in the Andes-Amazon region between 1988 and 2019. First, we use the Landsat archive to map land cover and characterize the spatial patterns of change at the regional level. Second, to empirically identify the effect of conflict on land cover change, we employ a difference-in-difference approach using local conflict events data. During conflict (1988–2011), land cover in the Andes-Amazon remained relatively stable, however during the post-conflict period (2012–2019), the conversion from forest to agriculture increased by 40%. We find that forest cover surrounding conflict events (1 km radius) decreased significantly, on average by ~ 19% during conflict, which accelerated to ~ 30% in the post-conflict period. Similarly, agriculture expansion is most substantial during the post-conflict period, but exclusively in municipalities with population below the 50th percentile. Landscape metrics show that in peripheral municipalities (<50th), agriculture occurs in clumped distributions during the conflict period. Meanwhile, during the post-conflict period, this expansion happens more quickly, with significantly greater agricultural patch sizes than during the conflict period. We conclude that a slow implementation of conservation governance, the emergence of illegal land markets, and illicit land uses (i.e., coca and illegal cattle ranching) may accelerate land cover change in the coming years.     

Projecting long-term armed conflict risk: An underappreciated field of inquiry?

Little research has been done on projecting long-term conflict risks. Such projections are currently neither included in the development of socioeconomic scenarios or climate change impact assessments nor part of global agenda-setting policy processes. In contrast, in other fields of inquiry, long-term projections and scenario studies are established and relevant for both strategical agenda-setting and applied policies. Although making projections of armed conflict risk in response to climate change is surrounded by uncertainty, there are good reasons to further develop such scenario-based projections. In this perspective article we discuss why quantifying implications of climate change for future armed conflict risk is inherently uncertain, but necessary for shaping sustainable future policy agendas. We argue that both quantitative and qualitative projections can have a purpose in future climate change impact assessments and put out the challenges this poses for future research.     

The effect of the temporal resolution of the wind forcing on a central Mediterranean Sea model

The impact of the wind forcing temporal resolution in the central Mediterranean Sea is addressed using a numerical ocean circulation model. The model uses interactive surface fluxes based on the ERA-Interim 6-hourly atmospheric reanalyses except for the 10 m wind for which ERA5 hourly reanalyses are used. Additional temporal resolution (2, 3, 6, 12 and 24 h) wind sets are deduced from the ERA5 hourly data. An ensemble of simulations (six members) is then performed where only the temporal resolution of the wind forcing is changed. The impact of the temporal resolution is studied based on this set of simulations. The dependence of the surface wind stress and heat flux on the wind resolution is derived based on an analytical expression where the Weibull distribution is used to characterise the probability density function of the wind speed. Results from the analytical model are found close to those from the numerical model when a linear increase of the exchange coefficients with the wind speed is considered. Power input into the sea and surface heat loss both increase with the increase of the temporal resolution but at lower rates when approaching hourly forcing values. The increase of the latent heat loss at these high resolutions is small (~−0.8 Wm^-2) but still important, around 10–20% the Mediterranean basin heat budget (−5 to −7 Wm^-2). The increase of the wind forcing temporal resolution decreases the sea surface temperature (SST) and increases the sea surface salinity (SSS) with largest values in the shallow area of the Gulf of Gabès (eastern coast of Tunisia). A decrease of SSS is however noticed in some areas mainly northwest of the Tunisia coast. Hydrographical changes are also found in the Tunisia-Sicily channel. They are characterised by mesoscale structures with no remarkable change of the major water veins.