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.