With the improvement of weather forecasting and the development of technology,the measurements of meteorological satellites have gradually become an important supplement to conventional observations.Owing to its advantage of all-day observation,Advanced Microwave Scanning Radiometer (AMSR-E) measurements have been widely used in research on global environmental change.The AMSR-E data record is very important in climate change monitoring and data assimilation in numerical weather prediction,but man-made radiative signals are also received by the microwave instrument and interfere with the natural thermal emissions of Earth.This phenomenon of satellite observations being mixed with signals from active microwave transmitters is referred to as Radio-Frequency Interference (RFI).RFI causes severe contamination of passive and active microwave sensing observations and corresponding retrieval products over some continents.The presence of RFI signals will reduce the scientific value of satellite measurements,so RFI signals should be detected and filtered before applying the microwave data in retrieval and data assimilation.With the long-term AMSR-E data being used in climate research,the characteristics of RFI signals also need to be analyzed.This paper focuses on the characteristics of RFI signals from AMSR-E data and their trend from September 2002 to September 2011.In this study,firstly,the spectral difference method and double principal component analysis (DPCA) method are used to obtain the spatial distribution of RFI signals.Compared to the spectral difference method,the DPCA method can detect RFI signals even over snow-covered areas,by taking advantage of the correlation of different channels for natural and snow radiation,and the de-correlation caused by RFI,and it is more robust and suitable for application worldwide.Then,the DPCA method is chosen to detect the RFI signals from the AMSR-E data over land from September 2002 to September 2011,and the trend of RFI signals with time is analyzed.The results show that the DPCA method can identify the RFI signals from brightness temperature of AMSR-E over land effectively,and can avoid the scattering effect of snow surfaces.The RFI signals from AMSR-E detected by the DPCA method are distributed mainly over the United States,East Asia and the India-Arabia Peninsula on C-band channels,and over Europe and East Asia on X-band.Strong RFI signals are mainly concentrated in populated cities.The locations of RFI signals are almost the same for horizontal polarization and vertical polarization channels;and RFI for horizontal polarization is stronger than that for vertical polarization.The areas and positions of RFI signals change with time,and their intensities are also not constant.The variation of RFI signals is probably due to changes in the human utilization of the radio spectrum,and obvious position changes may be related to the replacement of the infrastructure.The number of RFI signals detected by the DPCA method also varies with the seasons,being high in summer and low in winter in different regions except East Asia.From September 2002 to September 2011,the number of RFI signals decreased with time on C-band channels and increases on X-band.