Joint analysis of radio frequency interference from SMOS measurements and from airborne observations

The Soil Moisture and Ocean Salinity (SMOS) mission has been providing L-band brightness temperature observations since its launch in November 2009. SMOS observations are being utilized for soil moisture and ocean salinity estimation. However, the mission has been affected by significant levels of radio frequency interference caused by anthropogenic sources of radiation in the 1400-1427 MHz band. SMOS has only one frequency channel and measures brightness temperatures with 1.2 seconds time resolution, therefore the detection and mitigation of RFI is challenging, especially for low-level RFI. One possible approach for RFI detection involves use of the fully polarimetric properties of SMOS measurements. In this paper, an examination of the characteristics of SMOS measurements over the USA is first reported. SMOS measurements from Fall 2010 are then compared with RFI source information obtained from a Fall 2008 airborne campaign called SMAPVEX08 (which supported NASA´s Soil Moisture Active/Passive (SMAP)). The SMAPVEX08 “ground truth” information on RFI sources is used to examine possible RFI detection strategies using SMOS polarimetric data. Although the study is limited by possible changes in source properties in the intervening two year period, the results suggest that polarimetry can be used as an indication of some RFI sources, but may not reflect the RFI characteristics of a region in general.