Glancing over RFI sources

The Microwave Imaging Radiometer with Aperture Synthesis (MIRAS) instrument onboard SMOS is a Y-shaped antenna with a total of 72 receivers distributed along its three arms and central body. Each receiver captures the thermal radiation in the microwave L-band, more specifically in the protected passive band comprised between 1400 and 1427 MHz. Since the emission within this band is prohibited by the International Telecommunications Union (ITU), no relevant external interferences were expected before SMOS launch (2009). Nevertheless, the real situation is that the Radio Frequency Interferences (RFI) are present in large areas of Europe and Asia leading to low quality measurements. Moreover, due to the MIRAS interferometric processing, RFI sources located far away, even beyond the MIRAS Field of View (FOV), can contaminate large portions of the MIRAS image.

Retrieved L2 values. Ascending passes. Year 2012

Figure 1. Map of the number of retrieved L2 SSS values during 2012 for ascending passes. White areas have no valid L2 SSS values along 2012.

For a given zone, RFI signals can be classified in terms of the mean life time of the interference as transient emissions or permanent emissions. The former have a limited temporal influence and are mainly produced by mobile sources (for instance ships in open ocean). The latter have a strong effect and may even systematically preventĀ  the retrieval of salinity or soil moisture.

Our Web Map Server service (based on ncWMS and Godiva2 developed by Reading e-Science Centre at the University of Reading) can be used to reveal the spatial distribution of persistent RFI over ocean. The presence of a RFI source reduces the number of valid measures in the zone. Thus, affected zones can be detected by mapping the L2 used measures parameter.

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