AirMOSS P-band RF interference experience

The NASA AirMOSS instrument is a P-band (UHF) fully polarimetric synthetic aperture radar designed to measure root-zone soil moisture. The radar currently operates in the 420-440 MHz band in North America. Narrowband communications signals are secondary users of this spectrum and contribute RF interference to the radar's operation. An adaptive RF interference filter based on the least-mean squares (LMS) algorithm developed for the GeoSAR UHF airborne SAR program has been adopted for use by AirMOSS. Characterization of the algorithm's effects on simulated point targets finds a 1.2 dB average amplitude error. Though this is within the 1.5 dB absolute calibration specification for the AirMOSS radar, RFI removal can be a large contributor to the total radiometric error budget. Experience during the first nine months of AirMOSS operations has applied the adaptive RFI removal on an as-needed basis due to multiplicative noise (MNR) increase and calibration concerns.