Identification And Analysis Of Radio-Frequency Interference Over East Asia To AMSR-2 Observations Of The New-added Frequency

Compare with the previous advanced microwave scanning radiometer-E (AMSR-E), the advanced microwave scanning radiometer-2 (AMSR-2) onboard the Japanese GCOM-W1 satellite added a new frequency at 7.3 GHz, in order to relieve the radio-frequency interference (RFI). Now known that a successful mitigation of RFI is achieved in AMSR-2 observations over North-America, but still unknown the condition over East-Asia. For the purpose of further studying the distribution and origin of the radio-frequency interference of the new-added frequency at 7.3 GHz, we based on the AMSR-2 observations from August 1st to 16th,2014, use absorbance subtraction method and double PCA (DPCA) method to identify the radio-frequency interference over east Asia land and ocean.Research shows that the 7.3 GHz RFI does exist over east Asia. RFI which influence the gyeonggi-do. Daegu South Korea, Bangladesh, Vietnam and South-East cambodia is stable and sustainable ground-based active source, while the RFI source of Japanese Island is the interference of the reflected geostationary communication or TV satellite downlink signals to the measurements of spaceborne microwave radiometer. The observations of spaceborne microwave radiometer of ascending portions of orbits are usually interfered over Japanese island, while descending portions of orbits are hardly interfered. The RFI location and intensity derived from the geostationary communication or TV satellite changes with time and radiometer scanning angle within observation period.The conclusion of using DPCA method to identify RFI is similar to the conclusion of absorbance subtraction method. This illustrate that using DPCA method to identify RFI over East-Asia land at 7.3 GHz is feasible, moreover, RFI features which identified by absorbance subtraction method is valid. However the proportion of the RFI is different in some area when using two method to identify, especially in Vietnam, South-East cambodia and Bangladesh, the proportion of RFI identifying by DPCA method is smaller than the proportion of RFI identifying by absorbance subtraction method, but when RFI is interferenced by the reflected geostationary communication or TV satellite downlink signals to the measurements of spacebome microwave radiometer, such as Japan Island, the proportion of RFI identifying by two method is similar.When identifying RFI of East-Asia land at 7.3 GHz in winter, the DPCA method is better than the absorbance subtraction method, because of the consideration of the correlative of different bands, using DPCA method to identify RFI from snow and ice underlying surface is more accurate, it does not generate any misjudgment and the adaptability is more extensive.Due to East-Asia ocean, the observations of spaceborne microwave radiometer of ascending portions of orbits are usually interfered over Tsushima Strait Japan Sea coast and the Ryukyu Island, while descending portions of orbits are hardly interfered. The RFI source which influence the Tsushima Strait Japan Sea coast and the Ryukyu Island is the interference of the reflected geostationary communication or TV satellite downlink signals to the measurements of spaceborne microwave radiometer.