基于随机森林的国产小卫星遥感影像分类研究

近年来随着小卫星数量与传感器类型的快速增加,急需研究和发展快速可靠的小卫星遥感影像分类方法。针对分类方法各具局限性、具体应用中最优分类器选取困难等问题,本文基于多分类器集成学习的思路,引入随机森林(Random Forests)方法用于小卫星遥感影像分类。采用灾害监测预报小卫星(HJ-1)、北京1号小卫星(BJ-1)两种国产小卫星多光谱遥感影像进行试验,并与传统分类方法进行比较,结果表明,随机森林比最大似然分类器(MLC)、支持向量机分类器(SVM)等具有更好的稳定性、更高的分类精度和更快的运算速度,具有很好的适用性。     

人促天然更新米槠次生林与杉木人工林乔木层碳贮量分配特征比较

以杉木人工林为对照,分析三明陈大人工促进天然更新形成的米槠次生林乔木层碳贮量及其随树种、径阶、高阶的分配特点．结果表明：米槠次生林乔木层物种丰富度高于杉木林,人促天然更新有利于保持乔木层的树种多样性．米槠次生林乔木层碳贮量为178．67t·hm^-2,高于杉木人工林（111．24t·hm^-2）．米槠次生林和杉木人工林均以单优树种碳贮量占绝对优势,但米槠次生林中大个体林木（大径阶、大高阶）的碳贮量远大于杉木人工林．与杉木人工林相比,米槠次生林呈现出异龄的林分结构,这可能是其能够保持高碳吸存和高树种丰富度的重要原因．     

Assessing the Impacts of Eurasian Snow Conditions on Climate Predictability with a Global Climate Model

On the basis of two ensemble experiments conducted by a general atmospheric circulation model (Institute of Atmospheric Physics nine-level atmospheric general circulation model coupled with land surface model, hereinafter referred to as IAP9L_CoLM), the impacts of realistic Eurasian snow conditions on summer climate predictability were investigated. The predictive skill of sea level pressures (SLP) and middle and upper tropospheric geopotential heights at mid-high latitudes of Eurasia was enhanced when improved Eurasian snow conditions were introduced into the model. Furthermore, the model skill in reproducing the interannual variation and spatial distribution of the surface air temperature (SAT) anomalies over China was improved by applying realistic (prescribed) Eurasian snow conditions. The predictive skill of the summer precipitation in China was low; however, when realistic snow conditions were employed, the predictability increased, illustrating the effectiveness of the application of realistic Eurasian snow conditions. Overall, the results of the present study suggested that Eurasian snow conditions have a significant effect on dynamical seasonal prediction in China. When Eurasian snow conditions in the global climate model (GCM) can be more realistically represented, the predictability of summer climate over China increases.     

欧亚中高纬春季地表感热异常与长江中下游夏季降水的可能联系

利用国家气候中心提供的中国区域753站降水观测资料、ECMWF逐月地表感热通量再分析资料和NECP/NCAR再分析资料,讨论了欧亚大陆中高纬春季地表感热异常与长江中下游夏季降水之间的联系及其相关的物理机制。分析发现欧亚大陆中高纬春季地表感热异常与长江中下游地区夏季降水存在显著的正相关:感热偏强期,长江中下游夏季降水偏多;感热偏弱期,长江中下游夏季降水偏少。春季感热异常偏强时,夏季东亚副热带西风急流主体位置偏东、强度偏强、范围偏大,长江中下游地区主要受辐合上升气流控制,水汽输送条件好,降水异常偏多。而春季感热偏弱时,情况大致相反,则夏季降水异常偏少。研究表明欧亚大陆中高纬春季地表感热通量异常变化对我国长江中下游夏季降水预测具有一定的指示意义。     

Modern Sphagnumδ13C signatures follow a surface moisture gradient in two boreal peat bogs,James Bay lowlands,Québec

Carbon isotopic composition of Sphagnum macrofossils can potentially be used as a palaeohydrological tool for peat‐based climatic studies since a relationship between Sphagnum δ¹³C values and peatland surface moisture has been presented in previous studies. In order to verify this hypothesis, modern Sphagnum δ¹³C values were measured along a moisture (microtopographic) gradient in two boreal peat bogs. Isotopic measurements were performed on bulk material of S. fuscum, S. magellanicum, S. capillifolium and S. pulchrum. Isotopic variations found within and between Sphagnum species along the microtopographic gradient were compared using analysis of variance. A significant positive correlation (P < 0.0001) was found between Sphagnum δ¹³C values and their position along the surface moisture gradient. Results show that ¹³C‐depleted values are related to low water table depths (WTD), while ¹³C‐enriched values correspond to a water table that is close to the peat surface. Although the mechanisms underlying carbon fractionation processes in mosses are not well understood, we demonstrate that water resistance to CO₂ diffusion is an important fractionation process that is observed in bulk Sphagnum δ¹³C measurements, since drier and wetter samples exhibit consistent and very different isotopic signatures. Copyright © 2008 John Wiley & Sons, Ltd.     

Millennial‐scale fire and vegetation history from a mesic hardwood forest of southeastern Wisconsin,USA

High‐resolution charcoal analysis of lake sediment cores was used to reconstruct the fire history from two sites in a mesic hardwood forest of south‐eastern Wisconsin located in the Kettle Moraine State Forest. Pollen data from the region indicate that the sites, which lie within 5 km of each other, have had a consistent presence of mesic hardwood forest for the last 6500 years. A pollen record from one of the sites confirmed the regional vegetation history and the charcoal analysis indicated that fire frequency at each site was temporally linked to regional drought. Periods of high fire occurrence occurred in connection with a region‐wide drought 4200 years ago and, over the last 2000 years, shorter‐scale regional droughts were centred at 1800, 1650, 1100, 1000, 800, 700 and 600 cal a BP. The fire histories indicate that the last 1000 years have had lower fire frequencies than the previous 6500 years and suggest that the mesic hardwood forests may be resilient to increases in fire that may result from future climate change. Copyright © 2011 John Wiley & Sons, Ltd.     

Hortonian overland flow from Japanese forest plantations—an aberration,the real thing,or something in between?

There is a growing opinion that poorly managed plantation forests in Japan are contributing to increased storm runoff and erosion. Here we present evidence to the contrary from runoff plots at two scales (hillslope and 0·5 × 2 m plots) for several forest conditions in the Mie and Nariki catchments. Runoff coefficients from small plots in untended hinoki forests were variable but typically higher than from better managed or deciduous forests during small storms at Nariki; at Mie, runoff during small events was highly variable from all small plots but runoff coefficients were similar for hinoki plots with and without understory vegetation, while the deciduous plot had lower runoff coefficients. Storm runoff was less at the hillslope scale than the plot scale in Mie; these results were more evident at sites with better ground cover. During the largest storms at both sites, differences in runoff due to forest condition were not evident regardless of scale. Dynamic soil moisture tension measurements at Nariki indicated that during a large storm, flow in the upper organic‐rich and root‐permeated soil horizons was 3·2 times higher than measured overland runoff from a small hinoki plot with poor ground cover and 8·3 times higher than runoff from a deciduous forest plot. On the basis of field observations during storms, at least a portion of the monitored ‘Hortonian overland flow’ was actually occurring in this near‐surface ‘biomat’. Therefore our field measurements in both small and large plots potentially included biomat flow in addition to short‐lived Hortonian runoff. Because overland flow decreased with increasing scale, rill erosion did not occur on hillslopes. Additionally, runoff coefficients were not significantly different among cover conditions during large storms; thus, the ‘degraded’ forest conditions appear not to greatly enhance peak flows or erosion potential at larger scales, especially when biomat flow is significant. Copyright © 2007 John Wiley & Sons, Ltd.     

1995年4－6月的全球地震动态

１９９５年第二季度，全球地震活动恢复到１９９４年的高水平态势：浅源地震频数猛增，并出现两次Ｍｓ７．７以上巨大地震。大洋岛弧带成为本季度地震活动中心。所罗门群岛有两次中强震。菲律宾萨马岛附近发生大震群。千岛群岛大震的余震未息。秘鲁北部和缅印边界各有一次中深源地震。希腊发生中强地震两次。萨哈林岛地震显示全球地震信息。     

Distribution of clay minerals in surface sediments from the eastern Barents and south-western Kara seas

Surface samples from the eastern Barents and south-western Kara seas have been analysed for clay mineralogy. Transport paths, the role of regional sources and local bedrock outcrops and the influence of hydrodynamic and glacigenous processes for clay distribution on the shelves are discussed in relation to central Arctic Ocean deep sea and sea ice sediments. Franz Josef Land and Novaya Zemlya show significantly different clay mineral associations. Although smectite concentrations are fairly high, Franz Josef Land can be excluded as a source for central Arctic sea ice sediments, which are relatively rich in smectite. In the Kara Sea, smectite concentrations in coastal sediments surpass even the Franz Josef Land concentrations. The large cyclonic gyre in the eastern Barents Sea between Novaya Zemlya and Franz Josef Land, which serves as a mixing zone between Arctic and North Atlantic water, is apparently reflected within the smectite distribution pattern. With the exception of Franz Josef Land, the area of investigation is typically low in kaolinite. In particular, coastal areas and areas north of Novaya Zemlya, influenced by the inflow of Arctic waters, show the lowest kaolinite concentrations. A high kaolinite occurrence within the Nansen Basin is most probably related to Franz Josef Land and emphasizes the importance of long-range downslope transport of sediments across the continental slope. The surface water circulation pattern in close interaction with local outcrops onshore Novaya Zemlya and locally restricted occurrences within the eastern Barents Sea significantly alter the illite dispersal pattern. Illite concentrations are lowest around Franz Josef Land. Chlorite is generally low in the area of investigation. Submarine outcrops and important chlorite occurrences onshore Novaya Zemlya bias its distribution pattern.     

Large-scale interannual variation of the summer monsoon over India and its empirical prediction

Large-scale interannual variability of the northern summer southwest monsoon over India is studied by examining its variation in the dry area during the period 1871–1984. On the mean summer monsoon rainfall (June to September total) chart the 800 mm isohyet divides the country into two nearly equal halves, named as dry area (monsoon rainfall less than 800 mm) and wet area (monsoon rainfall greater than 800 mm). The dry area/wet area shows large variations from one year to another, and is considered as an index for assessing the large-scale performance of the Indian summer monsoon. Statistical and fluctuation characteristics of the summer monsoon dry area (SMDA) are reported. To identify possible causes of variation in the Indian summer monsoon, the correlation between the summer monsoon dry area and eleven regional/global circulation parameters is examined. The northern hemisphere surface air temperature, zonal/hemispheric/global surface air and upper air temperatures, Southern Oscillation, Quasi-biennial oscillation of the equatorial lower stratosphere, April 500-mb ridge along 75°E over India, the Indian surface air temperature and the Bombay sea level pressure showed significant correlation. A new predictor parameter that is preceding year mean monsoon rainfall of a few selected stations over India has been suggested in the present study. The stations have been selected by applying the objective technique ‘selecting a subset of few gauges whose mean monsoon rainfall of the preceding year has shown the highest correlation coefficient (CC) with the SMDA’. Bankura (Gangetic West Bengal), Cuddalore (Tamil Nadu) and Anupgarh (West Rajasthan) entered the selection showing a CC of 0.724. Using a dependent sample of 1951–1980 a predictive model (multiple CC = 0.745) has also been developed for the SMDA with preceding year mean monsoon rainfall of the three selected stations and the sea level pressure tendency at Darwin from Jan–Feb to Mar–May as independent parameters.