真实大气望远镜条件下斑点掩模法像复原模拟实验

我们于1989—1990年对一种有效的天文高分辨率像复原方法—斑点掩模法进行了真实大气、望远镜条件下的模拟实验,得到了较好的结果。实验结果表明,取样期间大气统计特性不变和小方差条件的重要性。为满足这一条件,合适的探测器是必须的。     

1991年7月11日日食观测的图象复原

１９９１年７月１１日日食期间，在大熊湖天文台进行了白光观测．图象是用６５ｃｍ反射系统和ＯＳＬ的ＣＣＤ获得的．月亮边缘始终包含在视场之中，从模糊的月亮边缘轮廓推得了一维的视宁度点扩散函数（ＰＳＦ），其中包含了望远镜引起的畸变。当天的ＰＳＦ的宽度介于０．８到１．３弧秒之间。假设存在圆柱对称性，则可得到二维的ＰＳＦ。然后，运用视宁度函数，对所观测的白光像消卷积。复原方法将观测到的ｒｍｓ反衬值由５％增强到１８％；亮桥可能亮于正常的光球强度；暗的半影纤维可能暗到正常光球的５０％；而亮纤维可能达到正常光球值。     

Discovery of the Avon – Solent Fracture Zone and its relationship to Bath hot springs

 The hot springs of Bristol and Bath and two geothermal wells at Southampton are located on a 155-km-long Avon–Solent Fracture Zone extending in a NW–SE direction from the Severn Estuary to the English Channel. Initiated during the Variscan earth movements and reactivated in Miocene times, the structure, which extends across the English Channel to France, is still active. With this discovery, it should now be possible to throw fresh light on the origin and movement of the thermal water at Bath and thus to protect the hot springs from derogation by limestone quarrying. Received: 16 October 1995 · Accepted: 13 February 1996     

降水的统计降尺度预报及其空间相关性和时间连续性重建

利用欧洲中期天气预报中心(ECMWF)、日本气象厅(JMA)、美国国家环境预报中心(NCEP)以及英国气象局(UKMO)四个中心1~7 d日累计降水量集合预报资料,以中国降水融合产品作为"观测值",对我国地面降水量进行统计降尺度预报,并对预报降水的空间相关性和时间连续性进行重建。对降水量进行分级后,建立各个量级的回归方程进行统计降尺度预报。此外,还利用Schaake Shuffle方法重建丢失的空间相关性和时间连续性。结果表明,分级回归比未分级回归后的预报结果相关系数更高,预报误差更小,更接近观测值。Schaake Shuffle方法可以有效地改进降水预报的空间相关性和时间连续性,使之更接近实况观测,集合成员间的相关性也更好。     

高原湖泊中萝卜螺属壳体研究现状及展望

湖泊的古水文及古水化学重建是湖泊研究领域最具挑战性的工作之一。在湖泊、河湖相及高湖面沉积物中,萝卜螺属壳体化石广泛分布;而且现生萝卜螺属亦广泛地分布于全球的湖泊及河流。这些生物碳酸盐(文石)壳体成为一种潜在的和高分辨率的环境信息记录载体。近年来,萝卜螺属的生境及其壳体的稳定碳氧同位素和元素已经逐步被用于了解青藏高原及其他地区的古水文、古水化学和古气候的信息。然而,在萝卜螺属壳体如何记录其宿生水体的古水文、古水化学等信息,以及如何基于萝卜螺属壳体化石重建古环境等方面,仍有许多科学问题有待探索。本文在前人研究的基础上,侧重在作为环境信息载体的萝卜螺属的分类体系、生境研究及其应用和壳体指标(δ¹³C_shell,δ¹⁸O_shell,⁸⁷Sr/⁸⁶Sr,Sr/Ca和Mg/Ca)特征及其在环境重建中的应用等方面进行总结和展望。     

Spatiotemporal changes in agricultural land cover in Nepal over the last 100 years

In order to advance land use and land cover change (LUCC) research in Nepal, it is essential to reconstruct both the spatiotemporal distribution of agricultural land cover as well as scenarios that can explain these changes at the national and regional levels. Because of rapid population growth, the status of agricultural land in Nepal has changed markedly over the last 100 years. Historical data is used in this study, encompassing soils, populations, climatic variables, and topography. Data were revised to a series of 30 m grid cells utilized for agricultural land suitability and allocation models and were analyzed using a suite of advanced geographical tools. Our reconstructions for the spatiotemporal distribution of agricultural land in Nepal reveal an increasing trend between 1910 and 2010 (from 151.2 × 10² km² to 438.8 × 10² km²). This expanded rate of increase in agricultural land has varied between different eco, physiographic, and altitudinal regions of the country, significantly driven by population changes and policies over the period of this investigation. The historical dataset presented in this paper fills an existing gap in studies of agricultural land change and can be applied to other carbon cycle and climate modeling studies, as well as to impact assessments of agricultural land change in Nepal.     

Application of the EnKF and Localization to Automatic History Matching of Facies Distribution and Production Data

The performance of the ensemble Kalman filter (EnKF) for continuous updating of facies location and boundaries in a reservoir model based on production and facies data for a 3D synthetic problem is presented. The occurrence of the different facies types is treated as a random process and the initial distribution was obtained by truncating a bi-Gaussian random field. Because facies data are highly non-Gaussian, re-parameterization was necessary in order to use the EnKF algorithm for data assimilation; two Gaussian random fields are updated in lieu of the static facies parameters. The problem of history matching applied to facies is difficult due to (1) constraints to facies observations at wells are occasionally violated when productions data are assimilated; (2) excessive reduction of variance seems to be a bigger problem with facies than with Gaussian random permeability and porosity fields; and (3) the relationship between facies variables and data is so highly non-linear that the final facies field does not always honor early production data well. Consequently three issues are investigated in this work. Is it possible to iteratively enforce facies constraints when updates due to production data have caused them to be violated? Can localization of adjustments be used for facies to prevent collapse of the variance during the data-assimilation period? Is a forecast from the final state better than a forecast from time zero using the final parameter fields?To investigate these issues, a 3D reservoir simulation model is coupled with the EnKF technique for data assimilation. One approach to enforcing the facies constraint is continuous iteration on all available data, which may lead to inconsistent model states, incorrect weighting of the production data and incorrect adjustment of the state vector. A sequential EnKF where the dynamic and static data are assimilated sequentially is presented and this approach seems to have solved the highlighted problems above. When the ensemble size is small compared to the number of independent data, the localized adjustment of the state vector is a very important technique that may be used to mitigate loss of rank in the ensemble. Implementing a distance-based localization of the facies adjustment appears to mitigate the problem of variance deficiency in the ensembles by ensuring that sufficient variability in the ensemble is maintained throughout the data assimilation period. Finally, when data are assimilated without localization, the prediction results appear to be independent of the starting point. When localization is applied, it is better to predict from the start using the final parameter field rather than continue from the final state.     

Pleistocene glacial relief of the central part of Mt. Prokletije (Albanian Alps)

The central and highest area of Mt. Prokletije (Albanian Alps) is situated in northern Albania and eastern Montenegro (at 42°30′N). The highest peak is Maja e Jezerces (2694 m). Detailed geomorphological mapping was used to reconstruct the positions of former glaciers. The longest Ropojana glacier had a length of 12.5 km and surface of 20 km²; others include Valbona Glacier (9.5 km, 10.5 km²), Grbaja Glacier (5 km, 6.7 km²) and Bogićevica Glacier (6 km, 6.9 km²). Three series of moraines can be distinguished: the lowest at an average altitude of 990 m (average ELA 1750 m), the middle series at 1350 m (ELA 1942 m), and the highest at 1900 m (ELA 2123 m). As no advanced dating methods have yet been used to provide a numerical chronological framework for these features, hypotheses are made based on the comparison with the advanced studies of other similar mountains in the Mediterranean region. The moraines of the first stage (lowest series) correspond to one of pre-LGM glaciations (Middle or even Early Würmian), the second stage moraines probably correspond to LGM, and the third stage could be attributed to Younger Dryas. The mapping included a number of inactive and active rock glaciers, as well as three small active glaciers (surface 5 ha and less), at 1980–2100 m altitude, in the area close to Maja e Jezerces.     

Geothermal regime and Jurassic source rock maturity of the Junggar basin, northwest China

We analyze the thermal gradient distribution of the Junggar basin based on oil-test and well-logging temperature data. The basin-wide average thermal gradient in the depth interval of 0–4000 m is 22.6 °C/km, which is lower than other sedimentary basins in China. We report 21 measured terrestrial heat flow values based on detailed thermal conductivity data and systematical steady-state temperature data. These values vary from 27.0 to 54.1 mW/m² with a mean of 41.8 ± 7.8 mW/m². The Junggar basin appears to be a cool basin in terms of its thermal regime. The heat flow distribution within the basin shows the following characteristics. (1) The heat flow decreases from the Luliang Uplift to the Southern Depression; (2) relatively high heat flow values over 50 mW/m² are confined to the northern part of the Eastern Uplift and the adjacent parts of the Eastern Luliang Uplift and Central Depression; (3) The lowest heat flow of smaller than 35 mW/m² occurs in the southern parts of the basin. This low thermal regime of the Junggar basin is consistent with the geodynamic setting, the extrusion of plates around the basin, the considerably thick crust, the dense lithospheric mantle, the relatively stable continental basement of the basin, low heat generation and underground water flow of the basin. The heat flow of this basin is of great significance to oil exploration and hydrocarbon resource assessment, because it bears directly on issues of petroleum source-rock maturation. Almost all oil fields are limited to the areas of higher heat flows. The relatively low heat flow values in the Junggar basin will deepen the maturity threshold, making the deep-seated widespread Permian and Jurassic source rocks in the Junggar basin favorable for oil and gas generation. In addition, the maturity evolution of the Lower Jurassic Badaowan Group (J_1b) and Middle Jurassic Xishanyao Group (J_2x) were calculated based on the thermal data and burial depth. The maturity of the Jurassic source rocks of the Central Depression and Southern Depression increases with depth. The source rocks only reached an early maturity with a R₀ of 0.5–0.7% in the Wulungu Depression, the Luliang Uplift and the Western Uplift, whereas they did not enter the maturity window (R₀ < 0.5%) in the Eastern Uplift of the basin. This maturity evolution will provide information of source kitchen for the Jurassic exploration.