Modelling soil erosion in tropical environments using remote sensing and geographical information systems

Abstract

Soil erosion probability maps were produced under various case scenarios by accounting for uncertainties in the data and in the decision rule, using the Universal Soil Loss Equation (USLE), remote sensing and geographical information systems (GIS). This objective was realized by applying the Bayesian Probability Theory within IDRISI, a raster based GIS. The outcomes were two continuous probability soil erosion maps ranging from zero to 1. Comparing these maps with an earlier study indicates that accounting for the uncertainties has, in general, decreased the probability of soil erosion. Based on average readings for specific sites on the maps, increases in erosion risk under the second case scenario have had the highest impact on the highlands that is in the central, eastern, and northern regions of Langkawi Island, Malaysia. Assuming a 10% risk, this impact has increased by 11.98, 11.83 and 5.741% for high, medium and low soil erosion risk areas on the island respectively.     

Insufficient thermalization effects on determining fission-track ages

Fission-Track Dating (FTD) has been developed as a useful technique for geological studies. Parent elements are measured by counting 235 U tracks induced by thermal neutrons. If insufficient thermalization occurs, fission of 238 U and 232 Th will be induced, and further measurement error will be introduced. Therefore, whether the neutrons are well thermalized or not will affect the FTD results. Due to requirement of safe operation, the 101 reactor was terminated in 2007. By using the 492 reactor as the new thermal neutron reactor, our present paper will attempt to study the feasibility and the potential influence on FTD. By irradiating monitor glass SRM612 and CN5 in pairs, we will study the thermalization situation of the 492 reactor. Irradiated data show that thermal neutrons are not evenly distributed either in horizontal or in vertical dimension. Especially, horizontal heterogeneity is obvious. But we discovered that proper irradiation position in the reactor can meet the requirement of FTD. Under the current irradiation condition, we calculated and assessed the insufficient thermalization effects on determining fission-track ages. We found that the difference between the 232 Th/ 238 U ratios of samples and standards is the main factor to the experiment results. The results will not be affected if the 232 Th/ 238 U value of samples is equal to the standard samples. However, if the 232 Th/ 238 U ratio is larger than that of the standards, the results will be smaller than actual ages. Comparatively, the ages will be more than expected if the 232 Th/ 238 U ratio is less. Therefore, to reduce the irradiation error, we suggest either locating the position of irradiation strictly, or minimizing the influence of lateral heterogeneity by reducing the amount of each sample package. Additionally, accuracy of the experimental results can be improved by increasing standard samples to adjust ζ value and using the monitor of standard glass SRM612 and CN5 together.     

径向基函数算法中插值参数对DEM精度的影响

以多重对数径向基函数插值算法中的插值参数为研究对象,选取了5种不同地貌类型的离散点数据,使用中误差度量指标,研究光滑因子、搜索点数、搜索方向对DEM插值精度的影响,给出插值参数的"最优"取值区间,消除插值参数选择的随意性,更好地指导DEM建模的运用。     

一种利用零交叉点理论的改进SIFT特征提取算法

提出了一种利用零交叉点特征提取的改进SIFT算子用于遥感影像的自动匹配.将图像几何特征引入到尺度空间探测中,获得了重复性更高、更稳定的特征.采用近景数码大旋角数码立体像对和低空航摄立体像对进行了算法测试.实验表明,改进后的SIFT算子应用于遥感影像自动匹配,在特征提取重复率、匹配正确点数、匹配正确率上均有明显提升.     

一种利用纹理特征和朴素贝叶斯分类器检测近景影像植被的方法

针对植被对近景摄影测量自动滑坡监测影响严重的问题,提出了一种基于纹理特征和朴素贝叶斯分类器的滑坡植被区域检测算法。对算法的有效性、影像对比度拉伸以及样本训练通用性对检测植被区域的效果等若干问题进行了实验探讨。通过与基于视觉认知特征的检测方法比较,验证了本算法的实用性和有效性。实验结果表明,本文算法能够很好地检测出近景影像中的植被区域,结果比较满意。     

面向异构空间区域分片的3RM缝隙处理模型

针对分布式环境下区域分片片段间的各种原始缝隙,提出一种3RM(Three Relational Matrix)缝隙处理模型。该模型采用两阶段流程,第1步划分空间计算单元,对区域分片边界处的要素进行聚类分组;第2步对各个空间计算单元进行缝隙处理。模型研究区域分片边界处缝隙的描述和区分方法,依据要素拓扑关系、属性关系以及精度3种关系建立了3RM缝隙处理矩阵,发现线状和面状要素在分片数据边界处的38种潜在的缝隙,并建立了相应的缝隙处理方法。运用3RM模型对异构的土地利用分片数据进行缝隙处理试验,试验结果表明,本文提出的缝隙处理模型能够有效处理实际分片数据当中的各种缝隙。     

GALILEO系统在中国区域内的完好性分析

完善的完好性是伽利略卫星导航系统(Galileo)的重要特征之一,主要分析了Galileo系统在中国地区的完好性性能。简要介绍了Galileo系统,在此基础上利用仿真数据,分别从不同高度截止角、不同伪距误差和不同测站点等三个方面对Galileo系统在中国地区的完好性的影响进行了比较和分析,并得出有益的结论。     

基于暗原色的航空遥感影像薄雾去除与改进

本文对航空遥感影像的薄雾进行了研究,根据雾图像成像模型和基于暗原色先验知识,结合图像对比度的自适应调整,提出了一种对航空遥感影像薄雾去除的改进算法。采用数字航空相机DSS439获取的不同地物特征类型的应急遥感影像进行去雾实验,并对实验结果进行分析、比较与评价,验证了该方法的正确性和有效性。     

台风大风预报研究回顾

大风是台风引发的三大灾害之一,考虑到现有的台风大风研究相对较少、预报经验也比较不足,因此对其预报方法进行回顾总结具有十分重要的意义。从经验预报、统计预报、数值模式预报及数值预报产品释用等4个方向梳理了台风大风预报技术的研究与应用现状:天气图、卫星云图和雷达图是经验预报中非常重要的工具;统计预报根据方法的不同可细分为回归预报、客观相似预报和气候持续性预报;数值模式预报方面,国内外多家机构都研发了相应的台风大风预报产品;数值预报产品的释用目前则包含了动力释用、统计释用和人工智能释用。同时总结了上述4类预报方法各自的优势和不足。最后,讨论了未来研究与实际业务中进一步提高台风大风预报能力的可能发展方向。     

CMIP6与CMIP5对历史大气层顶和地表辐射收支模拟的时空对比

基于云和地球辐射能量系统观测数据集（CERES),对比分析了耦合模式比较计划第五（CMIP5）和第六阶段（CMIP6）模拟的历史大气层顶和地表辐射收支的年际变化和空间分布,明确了多模式间不确定性大的关键区域。结果表明：在年际尺度上,除地表向上长波辐射外,CMIP6的辐射分量的集合均值较CMIP5更接近于CERES观测值,全球地表向下短波辐射的高估和大气逆辐射的低估在CMIP6中分别降低了1.9 W/m²和3.3 W/m²。除大气逆辐射外,CMIP6的辐射分量在多模式间的一致性较CMIP5提高。在北极,CMIP6对大气层顶反射短波、大气层顶出射长波和地表向下短波辐射的模拟偏差较CMIP5大。在南北纬60°,CMIP6对大气逆辐射的模拟偏差较CMIP5大。其他区域CMIP6的辐射分量更接近CERES观测值。CMIP6模拟的地表向下短波辐射和大气逆辐射的不确定性较大区域面积较CMIP5减小,但不确定性极大区域面积无变化。地表净辐射的不确定性空间分布在两代CMIP间变化甚小。青藏高原、赤道太平洋、热带雨林、阿拉伯半岛和南极洲沿海依然是地球系统模式模拟辐射收支不确定性极大的关键区域。