Fog Detection over China's Adjacent Sea Area by using the MTSAT Geostationary Satellite Data

A fog threshold method for the detection of sea fog from Multi-function Transport Satellite (MTSAT1R) infrared (IR) channel data is presented.This method uses principle component analysis (PCA),texture analysis,and threshold detection to extract sea fog information.A heavy sea fog episode that occurred over China's adjacent sea area during 7 8 April 2008 was detected,indicating that the fog threshold method can effectively detect sea fog areas nearly 24 hours a day.MTSAT-1R data from March 2006,June 2007,and April 2008 were processed using the fog threshold method,and sea fog coverage information was compared with the meteorological observation report data from ships.The hit rate,miss rate,and false alarm rate of sea fog detection were 66.1%,27.3%,and 33.9%,respectively.The results show that the fog threshold method can detect the formation,evolution,and dissipation of sea fog events over period of time and that the method has superior temporal and spatial resolution relative to conventional ship observations.In addition,through MTSAT-1R data processing and a statistical analysis of sea fog coverage information for the period from 2006 to 2009,the monthly mean sea fog day frequency,spatial distribution and seasonal variation characteristics of sea fog over China's adjacent sea area were obtained.

Spacecraft potential variations of the Swarm satellites at low Earth orbital altitudes

In this study, we provide the first detailed analysis of variations in the spacecraft potential (Vs) of the three Swarm satellites, which are flying at about 400-500 km. Unlike previous studies that have investigated extreme charging events, usually with spacecraft potentials as negative as −100 V, this study is focused on variations of Swarm Vs readings, which fall within a few negative volts. The Swarm observations show that spacecraft at low Earth orbital (LEO) altitudes are charged only slightly negatively, varying between −7 V and 0 V, with the majority of recorded potentials at these altitudes clustering close to −2 V. However, a second peak of Vs data is found at −5.5 V, though the event numbers for these more-negative observations are less, by an order of magnitude, than for incidents near the −2 V peak. These two distinct Vs peaks suggest two different causes. We have thus divided the Swarm spacecraft Vs data into two categories: less-negatively charged (−5 < Vs < 0 V) and more-negatively-charged (−6.5 < Vs < −5 V). These two Vs categories exhibit different spatial and temporal distributions. The Vs observations in the first category remain relatively closer to 0 V above the magnetic equator, but become much more negative at low and middle latitudes on the day side;at high latitudes, these first-category Vs readings are relatively more-negative during local summer. Second-category Vs events cluster into two bands at the middle latitudes (between ±20°-50° magnetic latitude), but with slightly more negative readings at the South Atlantic Anomaly (SAA) region;at high latitudes, these rarer but more-negative second-category Vs events exhibit relatively more-negative values during local winter, which is opposite to the seasonal pattern seen in the first category. By comparing Vs data to the distributions of background plasma density at Swarm altitudes, we find for the first category that more-negative Vs readings are recorded at regions with higher background plasma density, while for the second category the more-negative Vs data are observed at regions with lower background plasma density. This can be explained as follows: the electron and ion fluxes incident on Swarm surface, whose differences determine the potential of Swarm, are dominated by the background “cold” plasma (due to ionization) and “hot” plasma (due to precipitated particles from magnetosphere) for the two Vs categories, respectively.

Error Analysis of Orbit Determination for the Geostationary Satellite with Single Station Antenna Tracking Data

In the study, position and velocity values of a geostationary satellite are found. When performing this, a MATLAB algorithm is used for Runge-Kutta Fehlberg orbit integration method to solve spacecraft’s position and velocity. Integrated method is the solution for the systems which mainly work with a single station. Method provides calculation of azimuth, elevation and range data by using the position simulation results found by RKF. Errors of orbit determination are analysed. Variances of orbit parameters are chosen as the accuracy criteria. Analysis results are the indicator of the method’s

Recent Progress of Fengyun Meteorology Satellites

After nearly 50 years of development, Fengyun(FY) satellite ushered in its best moment. China has become one of the three countries or units in the world(China, USA, and EU) that maintain both polar orbit and geostationary orbit satellites operationally. Up to now, there are 17 Fengyun(FY) satellites that have been launched successfully since 1988. There are two FY polar orbital satellites and four FY geostationary orbit satellites operate in the space to provide a huge amount of the earth observation data to the user communities. The FY satellite data has been applied not only in the meteorological but also in agriculture,hydraulic engineering, environmental, education, scientific research and other fields. More recently, three meteorological satellites have been launched within the past two years. They are FY-4 A on 11 December2016, FY-3 D on 15 November 2017 and FY-2 H on 5 June 2018. This paper introduces the current status of FY meteorological satellites and data service. The updates of the latest three satellites have been addressed.The characteristics of their payloads on-boarding have been specified in details and the benefit fields have been anticipated separately.

Fengyun Satellites:Achievements and Future

Chinese meteorological satellite,Fengyun(FY) Satellite,has a polar-orbiting series and a geostationary series.Up to now,5 polar-orbiting(FY-1A/B/C/D and FY-3A) and 5 geostationary(FY-2A/B/C/D/E) satellites were launched.FY data has been being intensively applied not only to meteorological monitoring and prediction but also to many other fields regarding ecology,environment,disaster,space weather and so and.The FY data sharing system,FengyunCast,is now one of the three components of global meteorological satellite information dissemination system,GEONETCast.The first satellite of the new generation polar-orbiting series,FY-3A,was launched on 27 May,2008,demonstrating the FY polar-orbiting satellite and its application completed a great leap to realize threedimensional observations and quantitative application.The first of the next generation geostationary series(FY-4) is planned to launch in 2014.

GEOSTIONARY METEOROLOGICAL SATELLITE FY-2 OF CHINA

The first FY-2 geostationary metebrological satellite was lauched June 10, 1997flom Xichang satellite launching center by Long March-3 launching vehicle.This paper is to provide users with a brief description of the satellite system including primary objective, major payload, satellite specifications and data broadcasting system.

Primary Analysis of Development Approach to Chinese Satellite Mobile Communication

The paper describes the development of mobile communication first and then points out that it is necessary for China to develop satellite mobile communication after comparing the cellular mobile communication with the satellite mobile communication. After comparing the geostationary satellite system with the low earth orbit satellite mobile communication system, as well as the single-beam system with the multibeams system, both used in satellite mobile communication, we suggest that China, according to its economic status and level of satellite technology, should develop a geostationary multibeam satellite for its domestic mobile communication.

Novel evaluation method of TCP performance over satellite links

A novel and efficient method to evaluate the transmission control protocol （TCP） performance over satellite links is presented. A TCP module is divided into three functional blocks, namely data processing, congestion control and error control The re-established TCP module is easy to update TCP congestion control strategy or error control strategy. With the proposed analysis approach, the interactions between different congestion control and error control mechanisms, as well as the performanee of various combination protocols in satellite environments have been investigated. Simulation results obtained through a series of experiments have shown that SNACK-based error control strategy can perform well with any other congestion control strategy. The best performanee can be achieved by TCP NewReno congestion control strategy and SNACK-based error control strategy.

Efficient enhancing scheme for TCP performance over satellite-based internet

Satellite link characteristics drastically degrade transport control protocol （TCP） performance. An efficient performance enhancing scheme is proposed. The improvement of TCP performance over satellite-based Interuet is accomplished by protocol transition gateways at each end of a satellite link. The protocol which runs over a satellite link executes the receiver-driven flow control and acknowledgements- and timeouts-based error control strategies. The validity of this TCP performance enhancing scheme is verified by a series of simulation experiments. Results show that the proposed scheme can efficiently enhance the TCP performance over satellite-based Internet and ensure that the available bandwidth resources of the satellite link are fully utilized.

COSPAR International Constellation of Small Spacecraft

The Committee on Space Research(COSPAR)in 2019 established a new Task Group to develop an“actionable”plan for an international constellation of small satellites.As a background for taking such an approach,COSPAR quoted from its March 2019 Strategic Plan.

Convective Storm VIL and Lightning Nowcasting Using Satellite and Weather Radar Measurements Based on Multi-Task Learning Models

Convective storms and lightning are among the most important weather phenomena that are challenging to forecast.In this study,a novel multi-task learning(MTL)encoder-decoder U-net neural network was developed to forecast convective storms and lightning with lead times for up to 90 min,using GOES-16 geostationary satellite infrared brightness temperatures(IRBTs),lightning flashes from Geostationary Lightning Mapper(GLM),and vertically integrated liquid(VIL)from Next Generation Weather Radar(NEXRAD).To cope with the heavily skewed distribution of lightning data,a spatiotemporal exponent-weighted loss function and log-transformed lightning normalization approach were developed.The effects of MTL,single-task learning(STL),and IRBTs as auxiliary input features on convection and lightning nowcasting were investigated.The results showed that normalizing the heavily skew-distributed lightning data along with a log-transformation dramatically outperforms the min-max normalization method for nowcasting an intense lightning event.The MTL model significantly outperformed the STL model for both lightning nowcasting and VIL nowcasting,particularly for intense lightning events.The MTL also helped delay the lightning forecast performance decay with the lead times.Furthermore,incorporating satellite IRBTs as auxiliary input features substantially improved lightning nowcasting,but produced little difference in VIL forecasting.Finally,the MTL model performed better for forecasting both lightning and the VIL of organized convective storms than for isolated cells.

Observations from Fengyun Satellites

Fengyun(FY) Satellite has a polar-orbiting series and a geostationary series.Up to now,7 polar-orbiting(FY-1A/B/C/D and FY-3A/B/C) and 7 geostationary(FY-2A/B/C/D/E/F/G)satellites were launched.FY data has been being intensively applied not only to meteorological monitoring and prediction but also to many other fields regarding ecology,environment,disaster and so on.

A Unified Satellite Taxonomy Proposal Based on Mass and Size

The classification of spacecraft by mass is one of the main metrics to define the size of launch vehicles and the costs of launching satellites into orbit. The existence of many classifications (based on size categories and mass range values) makes inaccurate their common global characterization. This paper presents a review of the main satellite classifications schemes and a brief discussion about the current trends in the launcher market as an input to the satellite classification. Based on mass and size ranges and considering previous schemes and launching capabilities, a new classification arrangement is then proposed. According to the new scheme, satellites are grouped into 10 categories following specific rules depending on mass and size. In addition to unifying previous definitions of categories for small satellites, our new spacecraft taxonomy has the advantage of creating classes for very large space devices, such as space stations and potential interplanetary exploration missions.

A MEO Tracking and Data Relay Satellite System Constellation Scheme for China

A medium earth orbit （MEO） tracking and data relay satellite system （TDRSS） constellation scheme for China is proposed. This system consists of MEO satellite constellation, inter-satellite links （ISLs） and terrestrial gateway station, which can provide continuous bidirectional data transmission links between low altitude spacecrafls and the terrestrial gateway station in China. Theoretical analysis and simulation results indicate that the proposed constellation can cover the global low altitude space sphere and earth surface of China continuously, and has a preferable practical perspective.

基于静止气象卫星监测西太平洋火山活动

利用自主开发的静止气象卫星实时热点监测系统所积累的西太平洋2020~2023年卫星热点监测数据,结合全球火山活动计划(GVP)发布的全新世火山列表数据,在分析火山活动热辐射特征的基础上,提出一种基于静止气象卫星热点观测数据的火山活动监测算法,通过聚类识别技术从卫星热点数据中提取火山热点并计算火山热辐射指数。对比分析火山监测结果与GVP火山活动报告可知,该算法的火山活动识别率约为90%。漏报火山主要位于印度尼西亚地区,受火山活动类型和热带对流云系的影响。根据火山热点地理分布及其时间变化可以估算熔岩流蔓延方向、距离和速度。卫星火山热点监测数据在实时运行模式下可以作为输入因子之一驱动火山活动预报模型实时发布火山预警信息,其历史数据还可以作为高时间分辨率数据源支持火山活动研究。

大幅宽面阵相机多片探测器影像拼接方法

大幅宽面阵相机通常采用多片探测器拼幅成像的方式来增大幅宽。为了提高数据的使用效率,用户要求提供几何无损和视觉无缝的拼接产品。由于分片探测器间重叠区域小甚至无重叠区,拼接后影像畸变增大等原因,传统像方拼接方法难以适用。针对此问题,文章提出一种基于传感器校正的大幅宽面阵相机多片探测器影像高精度几何拼接方法。该方法首先根据卫星相机分片探测器的物理结构及其成像几何特性,虚拟一个完全理想的无畸变面阵影像,影像覆盖范围与原始分片探测器影像覆盖范围相同;在严格标定分片探测器像元指向的基础上,建立虚拟影像与原始分片影像的像点坐标换算关系,并将原始分片影像的像点灰度值赋给虚拟影像对应像点,进而实现对分片影像的无缝拼接和畸变校正。经对仿真数据和在轨数据的试验验证,结果表明:对于不同探测器拼接方式和搭接区重叠情况,文章中所提方法可获得视觉无缝和几何无损的拼接影像,影像的片间拼接精度和影像内部几何畸变均优于1个像素。

基于Himawari和FY4卫星实时监测森林火灾蔓延初探

探讨了新一代静止气象卫星在森林火灾蔓延速度测量中的应用潜能。Himawari-AHI和FY4-AGRI传感器10 min和5 min高时间分辨率观测数据为实时监测森林火灾蔓延速度(Fire Spread Rate,FSR)创造了有利条件。卫星遥感2 km空间分辨率观测下,绝大部分森林火灾火场蔓延变化周期大于12 min,说明新一代静止气象卫星观测数据有能力追踪测量森林火灾蔓延动态。本文提出一种基于Himawari-AHI和FY4-AGRI传感器的森林火灾蔓延速度测量算法,案例研究结果表明:该算法能够以较高精度给出近实时火场蔓延线速度和面积速度,线速度结合面积速度可以完整地描述火场整体蔓延趋势。蔓延算法可为林火蔓延预报研究提供一种实测数据源。

北斗系统GEO卫星伪距多路径误差改正

北斗系统地球静止轨道(GEO)卫星因相对于地面近似静止,其多路径误差相对于其他类型较为严重,且表现出系统波动现象。为提升定位精度,本文在GEO卫星伪距多路径误差特征研究的基础上,采用奇异谱分析方法对其进行修正,并通过伪距单点定位(SPP)验证伪距多路径误差修正效果。选取测站CUT0连续10d的静态观测数据进行修正试验。研究发现,GEO卫星伪距多路径误差序列表现出较强的天重复性,且多路径误差中的系统误差项越大,重复性也越强;在运用奇异谱分析方法修正GEO卫星伪距多路径误差各系统误差项后,多路径组合(MP)观测值和SPP的定位精度均有一定程度提升。

GOES-16 ABI观测和ERA5全天空模拟亮温揭示的热带对流水平特征尺度对比分析

本研究通过将GOES-16 ABI观测亮温和ERA5再分析资料的全天空模拟亮温进行对比分析,发现观测亮温和模拟亮温对流低值区位置大体接近,也能够定性反映出对流从发展到减弱的日变化过程,但亮温低值区域的强度存在较大差异。即使把高分辨率ABI通道13观测亮温平均到ERA5分辨率(0.25°×0.25°),在热带对流区的低亮温强度仍然高于ERA5全天空模拟亮温。因此利用主成分分析(Principal Component Analysis,PCA)和离散傅里叶变换(Discrete Fourier Transform,DFT)对任意选择的两对流区域内的观测和模拟亮温进行了尺度分析和对比。在其中对流较强的区域内,当ABI观测亮温的主成分分量从1增加到9时,水平特征尺度从700 km逐渐减小到150 km。ERA5全天空模拟亮温从主成分1增加到4时,水平特征尺度从950 km减小到270 km空间尺度,但当主成分4增加到9时,特征尺度几乎不变。在对流较弱的另一区域也能够发现ERA5模拟亮温对对流水平特征尺度有明显高估。ERA5模拟亮温各主成分的相位和观测亮温存在2 h以内的误差。由于ERA5全天空模拟亮温低值区与ERA5云冰路径大值区吻合度较高,由此可以推测ERA5云冰路径误差是造成ERA5全天空模拟亮温与ABI观测亮温差别的主要原因之一。

利用FY-4B地球静止气象卫星观测南海北部内孤立波及传播速度

本文利用中国新一代静止轨道气象卫星FY-4B数据开展了南海北部海域内孤立波观测及传播速度研究。首先使用500 m分辨率的全圆盘ARGI数据对FY-4B卫星可观测内波区域进行了讨论,确认了南海北部为研究区域。之后利用250 m分辨率的GHI数据使用多时相图像比较法(Multitemporal Image Comparison Method,MTI)计算了南海北部内孤立波的传播速度,其平均传播速度为1.78 m/s,东部深海区平均传播速度为3.02 m/s,向西传播至东沙群岛附近后平均速度减小至1.90 m/s,经过东沙群岛分裂后南部比北部传播速度更快,分别为2.08 m/s和1.54 m/s;最终在向西传播到近岸区域后内孤立波传播速度减小至0.42 m/s,直至最终消散。将MTI方法与两层模式下扩展KdV方程(extended Korteweg-de Vries,eKdV)计算得到的理论传播速度进行了对比,二者相关系数达到了0.89,证明eKdV理论方程对南海北部内孤立波传播速度反演的可行性,但仍具有一定的局限。最后将实测数据与遥感影像匹配计算内孤立波传播速度的结果与单一遥感影像计算内孤立波传播速度的结果进行了比较,两者相关性达到了0.93。本文验证了静止轨道卫星光学遥感数据的高时间分辨率特点对内孤立波传播速度研究具有的较大优势,对南海北部内孤立波参数反演等研究工作具有一定意义。