Development of a cloud detection method from whole-sky color images

A method is proposed for detecting clouds from whole-sky color images obtained with an all-sky camera (ASC) system. In polar regions, cloud detection using whole-sky images usually suffers from large uncertainties in fractional cloud cover retrievals because of large solar zenith angles (SZAs) and high surface albedo, which cause “whitening” in the images. These problems are addressed by using differences between real images and virtual clear-sky images for a particular observation time with the same SZA. The method is applied to ASC images obtained at Ny-Ålesund, Svalbard in May of 2005–2007, and the results are compared with Micro-Pulse Lidar (MPL) measurements. When no clouds were detected by MPL, the false cloud detection rate from ASC classification was 2.1% in total hours. Conversely, when clouds were detected by MPL, the ASC classification underestimated the clouds by 11.6%. In most cases, this occurred when MPL detected very optically thin clouds. Furthermore, the variability of cloud fractions estimated by MPL and ASC was roughly constant regardless of the SZA. Thus, it is confirmed that the method developed in this study is valid for cloud detection from whole-sky color images.     

Gamma-burst positions - are they reliable?

Ever since the discovery of the Cosmic Gamma-Ray Bursts we have searched for the quiescent counterparts of these mysterious flashes. Without definite counterparts our pictures of the sources must remain vague. The review discusses a number of techniques which have been applied to the gamma burst localization problem and their limitations. The most accurate technique to-date is the Interplanetary Network (IPN) timing technique. Considering the lack of success in the searches for counterparts in even the smallest gamma burst error boxes, it seems, that the next generation of satellite gamma burst detectors must be designed to allow immediate follow-up with sensitive telescopes. Concepts to achieve this goal are discussed.     

基于机器学习的极光图像自动分割方法

极光是太阳风能量注入到极区的指示器,从观测视野中准确分割出极光区域对研究极光演变如亚暴过程有非常重要的意义.本文基于全卷积神经网络提出了一种弱监督极光图像自动分割策略,数据标记时仅需指定极光区域的一个像素点即可,极大解决了机器学习人工标注数据的压力.首先利用简单单弧状极光图像训练一个初始分割模型Model 1,然后基于该模型,结合热点状和复杂多弧状极光图像获得一个增强的分割模型Model 2,最后对分割结果做进一步优化.本文对2003—2007年北极黄河站越冬观测的2715幅极光图像进行了分割,并和最新论文结果及人工标签进行了定量和定性比较,其中分割结果与人工标签的“交并比”高达60%,证明了本文方法的有效性.     

Relative Response of Biological and Non-Biological Monitors in a Coastal Environment

A field study was carried out in the spring and summer of 2003 (2 months each), to assess the efficiency of alternative exposure modes of biological monitors – lichen biomass and tree-bark biomass – together with prospective, non-biological monitors – cellulose acetate and Chelex-100 resin – versus conventional transplants of the same species. After exposure to the marine atmosphere of Sines (SW Portugal), saline elements (Cl, Na, K, Mg) contents were determined in all samples by instrumental neutron activation analysis (INAA). Manganese was used as the crustal reference for data normalisation. As a whole, the results pointed to a consistent elemental accumulation regardless of the season (spring, summer), and to some fair reproducibility of data. There were good correlations between Cl and Na in terms of both raw and normalised data, for either the biomonitors or the cellulose acetate. Elemental ratios generally agreed with the average relative composition of bulk seawater. The degree of association between Cl and Na appeared rather unaffected by the normalisation procedure, which suggests that (i) both elements most likely had an almost exclusive marine origin; and (ii) accounting for crustal inputs via Mn did not bias the results. Other sources than the sea-spray might contribute to the Mg levels, though, as only Mn-normalised data showed intrinsic (correlation) and extrinsic (ratio) consistency. The performance of the Chelex-100 resin was rather disappointing when compared to the other monitors.     

基于星点的全天空极光图像参数标定及其验证

全天空极光成像仪是地基极光观测研究的重要仪器设备,从其拍摄的全天空图像数据中能获得极光形态、尺度、激发强度等重要物理参数,因而精确标定全天空图像,对准确获取极光相关物理参数极为重要.本文提出了一种基于星点位置信息对全天空图像进行标定的方法,通过该方法可以确定全天空图像参数(天顶在全天空图像中的像素点位置,地理方位以及视野范围内成像半径与天顶角的关系).利用电离层卫星探测到的极光沉降电子能谱中的"倒V"结构与极光弧之间的对应关系,对星点标定方法获取的全天空图像参数进行了验证.结果显示卫星穿越的"倒V"结构宽度(60±6km、102±6km)与同时全天空极光成像仪观测到的卫星穿越的极光弧宽度(64.7±7km、111.6±7km)几乎一致,这表明本文提出的全天空极光图像参数的星点标定方法是有效和准确的.     

一种全天相机云图的自动处理方法

使用全天相机拍摄云图是现在天文界广泛使用的监测天空云量的方法。云量的估算结果对望远镜观测有重要的影响,目前对云量的估算完全由人工处理,费时、费力而且准确度不够高,判别过程也完全依赖个人的经验。为此,提出一种针对全天相机云图的云量自动计算方法。首先针对多云和少云云图分别使用时间分割法和差分法去除云图中月亮影响区域;然后对去除月亮影响区域后的多云云图进行二值化处理,将云与背景进行分割,并使用基于灰度值的聚类算法对少云云图的云的厚薄进行量化分类;最后计算总云量,并依据30 m口径望远镜(Thirty Meters Telescope,TMT)判读全天相机云图的方法对云图进行自动分类。实验结果表明,该方法可提高云图判读效率,在有效解放人工的同时,也达到了平均值为76. 67%的识别准确率。     

利用全天空可见光图像反演天空辐亮度

由中国科学院大气物理研究所LAGEO实验室研制和开发的地基全天空成像仪,可实现地基全天空自动化观测,文中首先对全天空成像仪仪器及性能进行介绍.辐亮度是气象科学研究中基础而重要的气象要素,而全天空成像仪记录的是可见光红、绿、蓝三波段辐射信息的灰度值图像,因而无法直接应用到气象研究中.为能够从灰度值图像中获取天空辐亮度信息,文中详细介绍了与亮度反演密切相关的几个重要标定实验,包括儿何标定、光学标定,以标定参数为基础并结合全天空仪器成像原理提出了一个由可见光灰度图像反演相对天空辐亮度分布的算式算法.文中还利用大气物理研究所香河观测站(39.75°N,116.96°E)同时观测的全天空成像仪以及CIMEL光度计所观测的天空辐亮度数据(440 nm波长),对该反演算式进行检验和比对,结果表明,所提出的算法进行天空辐亮度分布反演可行,该算法将灰度图像与天空辐亮度建立了联系,有利于观测图像数据与数值模式模拟工作的相互对比和验证,有利于观测图像数据在模式研究中的应用.     

Overview of Researches on All-Sky Satellite Microwave Data Variational Assimilation

As the important components of the earth’s atmospheric system, cloud and precipitation strongly affect the global hydrology and energy cycles through the interaction of solar and infrared radiation with cloud droplets and the release of latent heat in precipitation development. The microwave observations in cloudy and rainy conditions have a large amount of information closely related to the development of weather systems, especially the severe weather systems like typhoon and rainstorm. Nevertheless, satellite microwave observations are usually only assimilated in clear-sky above the ocean and their cloud and precipitation content is discarded. Over the past two decades, several Numerical Weather Prediction (NWP) centers have gradually developed the “all-sky” approach to make use of the cloud- and precipitation-affected microwave radiances. It’s been proved that the all-sky assimilation can be used to improve the first guessed mass, wind, humidity, cloud and precipitation through the tracer effect. For providing an investigated reference for the future research of all-weather assimilation in domestic numerical weather forecast, this paper reviewed the all-sky assimilation methods using microwave observation data, analyzed the advantages and disadvantages of each method, and discussed the key technical problems and the existing difficulties and challenges in this field. With the development and application of the new generation of NWP model in China, advancing the domestic research of all-weather data assimilation technology will bring more scientific and practical benefits in the future.     

Determination of the Velocity of Meteors Based on Sinodial Modulation and Frequency Analysis

In meteor photography the velocity of meteors is generally obtained from a chopper which blocks periodically the incident light beam in front of the camera lens. In this paper I examine modulation of the meteor trail instead with a sinodial function and use frequency analysis to compute accurately the mean atmospheric velocity.     

(极)年轻火山岩激光熔蚀40Ar/39Ar定年

对中国大量年轻或/和极年轻火山岩的定年实践研究表明,(极)年轻火山岩的激光熔蚀40Ar/39 Ar定年具有不同于第四纪以前喷发火山岩定年的显著特点.激光熔蚀40Ar/39Ar定年技术因为本底低、样品用量小以及与现代惰性气体同位素质谱设备在灵敏度、高精度方面的相一致,在年轻火山岩的定年中得到深入运用.借助激光在年轻或/和极年轻火山岩的40 Ar/39 Ar定年中,实践证明,样品形成时限越年轻(特别是相当于第四纪时期的样品),Nier值与样品中初始氩比值的偏离会引起K-Ar和40Ar/39 Ar表观年龄的偏差越大.对于小于0.2Ma的样品,Nier值与样品中初始氩比值的偏离对K-Ar和40Ar/39Ar表观年龄的偏差影响呈指数增长;当样品年龄相对较老(老于第四纪)时,Nier值和初始氩比值的偏离对K-Ar和40Ar/39 Ar表观年龄的影响较小.以40Ar/ArAr定年为出发点,定量给出界定年轻与极年轻火山岩的年龄:2～0.2Ma的火山岩界定为年轻火山岩,0.2Ma以来的火山岩称为极年轻火山岩.实验结果还证实,测定(极)年轻火山岩基质年龄时要尽量剔除非同源分馏的斑晶,以便去除斑晶可能带来的过剩氩影响;年轻火山岩样品的测年,应根据岩石结构和粒度特征选取合适的粒度,通常情况下,推荐0.2mm颗粒直径(60～80目)为理想粒径;年轻火山岩样品在快中子辐照后冷却放置时间不宜过长,否则造成37 Ar测不准,影响数据结果,带来较大偏差;激光40Ar/39Ar精细定年对标准样品的均一性有很高的要求,通过标定常用的国内外监测标样发现,标样SB-778-Bi,Bem4M,BT-1均一性很好,适合用作激光熔蚀40Ar/39Ar定年监测;测试数据的处理中,火山岩喷发后冷却结晶中同时形成的斑晶和基质的等时线处理能够帮助获得客观真实和精细的年龄结果.在此基础上,北京大学惰性气体同位素实验室建成了专用于(极)年轻火山岩精细定年的激光熔蚀40Ar/39Ar定年实验流程.