Radio Frequency Environment for Earth-Observing Passive Microwave Imagers

This paper examines the radio frequency interference (RFI) environment within microwave imager bands for sensors that have observed the earth over the last two decades. Since the microwave imagers have used various bands both within and outside of International Telecommunications Union (ITU) allocated frequencies for passive satellite earth exploration, this survey provides valuable insight into band selection and mitigation strategies for future missions. Several conclusions are drawn from this paper. First, significant land-based RFI exists at the C-Band. The two-band mitigation solution for the C-Band utilized by Advanced Microwave Scanning Radiometer 2 provides some RFI reduction of high-level RFI (> 10 K), and therefore, may have merit for future missions in cases where only two subbands can be feasibly implemented. At the X-band, ocean reflections from direct broadcast and communication satellites (especially around Europe) provide considerable interference above the ITU-allocated 10.6-10.7 GHz band, whereas very little reflected interference is observed within the allocated band. Good out-of-band rejection is required to avoid the reflected RFI above 10.7 GHz. Both inside and outside of the X-band allocation, significant terrestrial RFI exists. For the K-band, the 19.35-GHz band utilized by Special Sensor Microwave Imager Sounder and Tropical Rainfall Measuring Mission Microwave Imager avoids reflected RFI from satellites that is present around the continental United States for satellites observing within the 18.6 to 18.8 GHz allocated band. The analysis suggests that the 19.35-GHz band may be preferable to the 18.7 GHz allocated band for ocean applications if avoiding RFI is desired.