SWACI - Total Electron Content (TEC) Maps

SWACI is a research project of DLR supported by the State Government of Mecklenburg-Vorpommern. Radio signals, transmitted by modern communication and navigation systems may be heavily disturbed by space weather hazards. Thus, severe temporal and spatial changes of the electron density in the ionosphere may significantly degrade the signal quality of various radio systems which even may lead to a complete loss of the signal. By providing specific space weather information, in particular now- and forecast of the ionospheric state, the accuracy and reliability of impacted communication and navigation systems shall be improved. The total electron content (TEC) is defined as the integral of the electron density along the ray path between satellite and receiver. Thus, TEC provides the number of electrons per square meter. The most frequently used unit is 1TECU = 1x1016 electrons / m2. TEC is derived from dual frequency code and carrier phase measurements provided by Global Navigation Satellite Systems (GNSS). SWACI uses GPS measurements from various European GNSS networks such as the International GNSS Service (IGS), European Reference Frame (EUREF), Norwegian Mapping Authority (NMA), and ascos distributed by the Federal Agency of Cartography and Geodesy (BKG) Frankfurt. The global TEC maps are mainly created by using data provided by the International GNSS Service Real-Time Pilot Project (IGS-RTPP). To generate TEC maps of vertical TEC, the slant measurements have to be transformed to the vertical. In a first approximation the ionospheric range error in GNSS is proportional to TEC. These TEC maps are used to derive latitudinal and zonal gradients, rate of change of TEC (5 min increments), 27 days medians, hourly forecasts of TEC, and corresponding error estimates. Spatial resolution (latitude x longitude): 2 °x 2° (Europe), 2.5° x 5° (globally)SWACI是由梅克伦堡-前波美拉尼亚州政府资助的德国航空航天中心（DLR）研究项目。现代通信与导航系统发射的无线电信号可能会受到空间天气灾害的严重干扰。电离层电子密度的剧烈时空变化会显著降低各类无线电系统的信号质量，甚至可能导致信号完全丢失。通过提供特定的空间天气信息，尤其是电离层状态的现报与预报，本项目旨在提升受影响的通信与导航系统的精度与可靠性。 总电子含量（Total Electron Content, TEC）被定义为沿卫星与接收机之间射线路径的电子密度积分，因此TEC表示每平方米内的电子总数，其最常用的单位为1TECU = 1×10¹⁶ 电子/平方米。 TEC可通过全球导航卫星系统（Global Navigation Satellite Systems, GNSS）提供的双频码与载波相位观测值反演得到。SWACI项目使用来自多个欧洲GNSS网络的GPS测量数据，包括国际GNSS服务（International GNSS Service, IGS）、欧洲参考框架（European Reference Frame, EUREF）、挪威测绘局（Norwegian Mapping Authority, NMA），以及由德国联邦制图与大地测量局（Federal Agency of Cartography and Geodesy, BKG）法兰克福分部分发的ascos数据。全球TEC地图主要依托国际GNSS服务实时试点项目（International GNSS Service Real-Time Pilot Project, IGS-RTPP）提供的数据制作。 若要生成垂直TEC地图，需将斜向观测值转换为垂直方向。在一阶近似条件下，GNSS中的电离层测距误差与TEC成正比。 这些TEC地图可用于提取纬度梯度与纬向梯度、TEC变化率（以5分钟为间隔）、27天中位数、TEC逐小时预报以及相应的误差估算值。 空间分辨率（纬度×经度）：欧洲区域为2°×2°，全球范围为2.5°×5°