极地科考影音技术研究     

熊俊  孙立民  张延波  殷福忠 《东北测绘》2010,(1):213-214,217,220

极地科考影像资料是通过胶片模拟图像信号形式存储的。为了后期进行非线性编辑制作，有必要把胶片上存储的模拟图像信号转换为磁带录像电信号。通过深入地对比与研究，利用胶转磁技术完成这个工作是一个有效的方法。本文通过CCD胶转磁设备对极地科考影像资料进行胶转磁处理，并对转换后的影像资料与声音进行影音同步处理。  相似文献   

Evidence for the charge-excess contribution in air shower radio emission observed by the CODALEMA experiment     

《Astroparticle Physics》2015

CODALEMA is one of the pioneer experiments dedicated to the radio detection of ultra high energy cosmic rays (UHECR), located at the radio observatory of Nançay (France). The CODALEMA experiment uses both a particle detector array and a radio antenna array. Data from both detection systems have been used to determine the ground coordinates of the core of extensive air showers (EAS). We discuss the observed systematic shift of the core positions determined with these two detection techniques. We show that this shift is due to the charge-excess contribution to the total radio emission of air showers, using the simulation code SELFAS. The dependences of the radio core shift to the primary cosmic ray characteristics are studied in details. The observation of this systematic shift can be considered as an experimental signature of the charge excess contribution.  相似文献   

闪电气象学研究进展   总被引：13，自引：1，他引：12  

郄秀书  刘冬霞  孙竹玲 《气象学报》2014,72(5):1054-1068

闪电气象学是随着现代闪电探测和定位技术的发展与应用而不断发展起来的一个学科,也是大气电学和气象学的重要交叉学科分支。综述了近年来中国在闪电气象学方面的发展和研究进展,主要从5个方面进行阐述和回顾：在闪电气象学研究中发挥了重要作用的现代闪电探测和定位技术,不同类型强对流天气系统的闪电活动特征,闪电活动与雷暴的动力、微物理结构的关系,雷暴电荷结构探测和数值模拟,以及闪电资料同化方法及其在强对流天气中的预警预报作用和闪电的预报等,并指出了中国闪电气象学今后的努力方向。  相似文献   

Caesium-137 in Southeast Asia: Is there enough left for soil erosion and sediment redistribution studies?     

《Journal of Asian Earth Sciences》2013

Low reference inventories of the fallout radionuclide ¹³⁷Cs in low latitudes may limit its present and future application for studies of soil erosion and sediment redistribution in Southeast Asia. ¹³⁷Cs reference inventories and concentrations in surface materials measured in nine and five areas, respectively, across Southeast Asia are here reported and reviewed. The compiled reference inventories decrease from north to south. Three global estimates of ¹³⁷Cs total fallout are also reviewed and compared to the measured data while taking into account factors that affect the fallout estimates and the reference inventory. The results are presented as a schematic regional distribution map of ¹³⁷Cs reference inventories for the year 2012. A relationship between a reference inventory and topsoil concentration is also provided. The measured ¹³⁷Cs concentrations suggest that a minimum detectable activity (MDA) less than 0.5 Bq/kg is required for detection of ¹³⁷Cs activity in topsoils in the lowest reference inventory areas. This sensitivity should allow, at present, ¹³⁷Cs to be a useful tool for analysis of soil erosion in Southeast Asia, should also be a useful chronometer, and will be a useful tracer at least where the reference inventory is more than 500–600 Bq/m². This level of MDA has been demonstrated in previous studies to be achievable by gamma-ray spectrometry using non-destructive sample treatment. As the nuclide decays, sufficient will remain to be useful until the middle of this century in most areas in Peninsular Malaysia and southern maritime Southeast Asia, and a few decades more in the rest of the region.  相似文献   

First Phase Monitoring Studies of Simulated Benthic Disturbance Delineating Movement of Fine Particles in the Central Indian Basin     

A. B. Valsangkar 《Marine Georesources & Geotechnology》2013,31(4):357-371

Benthic disturbance due to future deep-sea polymetallic nodule mining would involve expensive sediment plume generation and resedimentation on the sea floor. In order to evaluate the effects of resedimentation on benthic environment, the Indian Deep-sea Environment Experiment (INDEX) was conducted in 1997, and pre-, and post-disturbance studies on grain size were carried out. The initial increase in clay content after the experiment, continued to increase further as measured in the first monitoring phase samples, 44 months later. Increase in clay-sized particles during monitoring-l (M-l) was highest within the simulated (disturbed) zone and to the north of it, which is attributed to the combined effects of disaggregation, abrasion, and powderization of sediments during transportation. Due to this fractionation (breaking up), the particles appear to have remained in suspension over a prolonged period of time after they were discharged in the water column 5 m above the seabed during INDEX. The travel effects of INDEX plume appears to be localized and confined within and around the disturbed zone (DZ) as resettlement of fine particles from the benthic plume was traced up to 2 km south and 12 to 18 km north of the DZ. The evidence does not suggest the existence of strong currents and benthic storms in the CIB  相似文献   

近距离地闪电场变化及对通道电荷密度分布的响应   总被引：1，自引：0，他引：1  

张其林  刘明远  杨璟  刘晓东  杨静  蒋如斌 《气象学报》2012,70(4):847-854

一般认为,如果回击过程将先导通道的电荷完全中和,则几十米到几百米范围内的近距离先导电场与回击电场的大小相同,否则,二者之间则存在一定的差异。为了对上述观点进行分析,将源电荷先导模式和MTLL回击模式组合建立了先导-回击模式(这两个模式的组合意味着先导通道的电荷被回击完全中和),对近距离先导-回击电场变化的"V"形结构进行了模拟分析。结果表明,即使假定先导电场被回击完全中和,在近距离30—550m范围回击电场与先导电场强弱关系并不确定。另外,根据进一步的讨论,上述模拟结果几乎不受其他因素,如土壤湿度(该因素直接决定土壤电参数)和地形起伏的影响。因此,在回击开始几十微秒内,基于地面测量的先导-回击电场之差来判断先导通道电荷是否被回击完全中和可能存在一定的不确定。  相似文献   

环境温湿层结对雷暴云空间电荷结构的影响   总被引：13，自引：3，他引：10  

郭凤霞  张义军  言穆弘  董万胜 《高原气象》2004,23(5):678-683

非感应起电机制中决定雷暴云电荷结构的反转温度是液态水含量的函数,而液态水含量的空间分布又取决于环境初始场中气团平均相对湿度和对流不稳定性的配置情况。本文通过不断改变初始场中层平均相对湿度和对流有效位能(CAPE)的值,同时不稳定度因子K和SI也随之发生相应的改变,利用三维强风暴动力电耦合数值模式,来研究初始场温湿层结的不同配置对液态水含量进而对电荷结构的影响。结果表明,CAPE较小时,电荷结构与中层平均相对湿度的大小无关,均为准反极性,且起电活动较弱;CAPE很大时,较大和较小的中层平均相对湿度更易引起强的起电活动和偶极性电荷结构,当霰和冰晶共存的区域中心落在上升气流的外围时,会形成反极性电荷结构。当对流有效位能相同时,增加中层平均相对湿度,气层的不稳定性提高,更有利于对流的发展和偶极性电荷结构的形成,减小中层平均相对湿度,对流减弱,有利于准反极性电荷结构的形成。  相似文献   

Characteristics and simulation of lightning current waveforms during one artificially triggered lightning     

Q. Zhang  X. Qie  Z. Wang  T. Zhang  Y. Zhao  J. Yang  X. Kong 《Atmospheric Research》2009,91(2-4):387-392

In the summer of 2005, one negative lightning flash was artificially triggered in Shandong Province (117°48′ E, 37°42′N), middle latitude region of eastern China. The flash included 10 return strokes, and the geometric mean value of the current peak was 11.9 kA (the average value was 12.6 kA) with a maximum of 21.0 kA and a minimum of 6.6 kA, similar to the subsequent return strokes in natural lightning. The geometric mean value of half peak width was 39 μs (the average value was 40 μs), which was much larger than the usual result. Based on the Diendorfer and Uman (DU) model, the return-stroke current waveforms and charge distribution along the lightning channel are discussed. The simulated current waveforms, being divided into breakdown and corona current components, are in agreement with the optical measurements when the two different discharge time constants are properly chosen.  相似文献   

Study of the total lightning activity in a hailstorm   总被引：1，自引：0，他引：1  

Joan Montany  Serge Soula  Nicolau Pineda  Oscar van der Velde  Pere Clapers  Glria Sol  Joan Bech  D. Romero 《Atmospheric Research》2009,91(2-4):430-437

A thunderstorm that developed over northeastern Spain on 16 June 2006 is analyzed. This severe thunderstorm produced hailstones as large as 40 mm and had a lifetime of 3 h and 30 min. Radar cross-sections show strong vertical development with cloud echo tops reaching an altitude of 13 km. The specific characteristics of the lightning activity of this storm were: (i) a large amount (81%) of negative cloud-to-ground (−CG) flashes with very low peak currents (< 10 kA in absolute value), (ii) a very large proportion of intra-cloud (IC) flashes with an IC/CG ratio reaching about 400, (iii) a large number of “short” IC flashes (with only 1-VHF source according to SAFIR detection), (iv) a large increase of the −CG flash rate and of the CG proportion near the end of the storm. The rate of −CG flashes with a low peak current were observed to evolve similarly to the rates of IC flashes. Most of them have been assumed to be IC flashes misclassified by the Spanish Lightning Detection Network (SLDN). They have been filtered as it is usually done for misclassified +CG flashes. After this filtering, CG flash rates remained very low (< 1 min^− 1) with +CG flashes sometimes dominant. All the particular lightning activity characteristics similar to those observed in the Severe Thunderstorm Electrification and Precipitation Study (STEPS) campaigns support the hypothesis that this thunderstorm could have had an inverted-polarity or complex charge structure. The maximum IC flash rate (67 min^− 1) peaked 24 min before the presence of reflectivity higher than 60 dBZ. The IC activity abruptly decreased during the period when reflectivity was dramatically increasing. The time of maximum reflectivity observed by radar was consistent with the times of reported hail at the ground.  相似文献   

雷暴电活动对冰雹增长影响的数值模拟研究   总被引：9，自引：0，他引：9       下载免费PDF全文

张义军  孙安平  言穆弘  郭凤霞  郄秀书  黄美元 《地球物理学报》2004,47(1):25-32

利用三维强风暴动力-电耦合模式,数值模拟了风暴演变过程 中电活动对冰雹增长及地面降雹的影响. 结果指出,带电冰雹与云内强电场作用使地面降雹 量增加约50[HTK]髎[HTSS],雹块直径增大0.7mm,降雹时间滞后约3min. 文中还讨论了强电 场通过对水成物降落速度的调制来影响冰雹微观增长过程,即主要是影响碰并过程和冰雹融 化过程. 电活动使冰雹源、汇总量都减少,但汇总量减少更多,总体效果使冰雹总量增加, 数目减少,冰雹长得更大,更易降落到地面.  相似文献