GIM和IRI2012模式在中国地区的时空变化和扰动分析

Temporal and spatial variation and perturbation analysis for China with GIM and IRI2012 model

在合成孔径雷达(SAR,Synthetic Aperture Radar)定位中,电离层延迟是不可忽略的误差源之一,需要选择合适的电离层模型进行校正.为了验证IRI2012模式和GIM模式在中国不同纬度地区的适用性以及中国地区电离层扰动与太阳耀斑、地磁场等因素的相关性,本文利用IRI2012模式计算的TEC预测值,并结合GIM模式给出的TEC观测值对2014太阳活动低年的中国不同纬度地区TEC时空变化特性进行了分析,包括周日变化、半年变化和年变化等.此外,由于电离层扰动引起的电离层延迟对星载低频SAR定位精度影响比较严重,以IRI2012模式为背景电离层,根据电离层平静期的GIM-TEC观测值确定电离层TEC扰动指数的阈值,在太阳耀斑和地磁异常发生时统计前后一定时间的电离层TEC扰动指数.实验结果表明:IRI2012模式和GIM模式在中国低纬和中高纬度地区的空间和时间变化均符合一般规律,在中国地区具有适用性;电离层扰动指数连续5小时超过阈值0.5判定为电离层扰动事件,当中国地区位于向阳面或处于日冕物质抛射区时,其上空电离层扰动与太阳磁暴和地磁暴紧密相关.

In the synthetic aperture radar （SAR, Synthetic Aperture Radar ） positioning system, ionospheric delay is an important error source that must be eliminated by ionospheric models, so selecting a suitable ionospheric model can effectively improve the SAR positioning accuracy. The total electron content （TEC, Total Electron Content ） is an important parameter to describe the state of the ionosphere. To verify the applicability of IRI2012 model and GIM model for different latitudes in China and the relationship between ionospheric disturbances in Chinese region and solar flares, geomagnetic field and other related factors, so in this paper, IRI2012-TEC predicted values and GIM-TEC observed values are used to analyze TEC Temporal and spatial characteristics in China in 2014 of low solar activity, including diurnal variation, season dependence, annual change and the long-term change. In addition, since that the influence of ionosphere delay caused by ionospheric disturbances on the SAR positioning accuracy is very serious, considering the IRI2012 model as a background ionosphere, with GIM-TEC observed values in ionosphere quiet period, threshold value of ionospheric TEC disturbance index was determined. The effects of solar and geomagnetic activity on Chinese ionospheric disturbances can be verified by comparison with the threshold value. The results showed that temporal and Spatial Variation of TEC generated by IRI2012 model and GIM model in Chinese low-latitude and high-latitude regions are in line with the general role, so the two models have applicability in China; Ionospheric disturbance index exceeding the threshold value of 0.5 for more than five hours is determined to be ionospheric disturbances event, Only if China region is located on the sunny side or in coronal mass ejection distinct, will the ionosphere over China region be subject to the impact of solar or geomagnetic activity.