Radio-Frequency Interference（ RFI） is an increasingly severe problem for present and future microwave satellite missions. It causes serious problems to passive and active microwave sensing observations and to corresponding retrieval products.Detecting RFI signals is an important step before data can be used. The Microwave Radiation Image（ MWRI） on board the Feng Yun（ FY）-3B satellite can provide the brightness temperature data at 10. 65 GHz

18. 7 GHz

23. 8 GHz

36. 5 GHz

and89 GHz

each having dual channels at horizontal and vertical polarization states. RFI signals are present in MWRI data over land and ocean. RFI signals from data over ocean are more difficult to detect than those over land because of the low microwave emissivity of the sea surface. In general

RFI signals are detectable by using a multichannel regression method and retrieval chi-square probability. However

the two methods need auxiliary brightness temperature data within a certain period of time under conditions without ice and RFI

and located away from the coast. In this study

we use multichannel regression and Double Principal Component Analysis（ DPCA） to identify the RFI signals from MWRI data over ocean. DPCA takes advantage of the decorrelation for RFI signals and the correlation characteristics of radiation data in different channels for nature surface

including snow cover and synoptic process. This method does not need auxiliary brightness temperature data

and it can been used to offer a real-time RFI detection method before data are provided. Compared with the results of multichannel regression

the results of DPCA can be considered effective in detecting RFI signals from MWRI ocean brightness temperatures. Moreover

the results obtained from the water near North America in winter indicate that multichannel regression produces false results over sea ice. The false signals could be avoided effectively in DPCA. The consistent results from different methods show that the RFI signals detected are credible. The RFI signals of MWRI at 10. 65 GHz horizontal polarization over ocean are distributed widely over the ocean of Europe

and these signals are present at the offshore marine areas of East Asia and North America.