中文摘要：

利用电离层层析技术对日本Ms9.0地震前21天震中区域附近上空电离层进行了三维重构,并通过2倍标准差方法对反演出的各时刻电离层各格网点电子密度值进行了异常探测。在排除太阳和地磁活动影响后分析得出：2月28日UT14：00—16：00出现的电离层电子密度值异常减小、3月2日UT08：00—14：00、3日UT00：00—06：00和4日UT12：00—20：00出现的电离层电子密度值异常增大极有可能与日本地震有关。

英文摘要：

By use of the technology of ionospheric tomography,three-dimension ionospheric electronic density in a time length of 21 days prior to Japan March 11,2011 earthquake were reconstructed over the epicenter area,and the electron density anomaly detection was conducted at all ionosphere grid network points for a specific time period.After excluding the effect of solar and geomagnetic activity,the computational results indicate that the abnormal ionospheric electron density decreased at the Universal Time（UT） of 14：00-16：00 on February 28 and increased at 08：00-14：00 on March 2,00：00-06：00 on March 3,and 12：00-20：00 on March 4.The occurrence of these anomalies is likely a precursor of the Japan Ms9.0 earthquake.