ADD:
Agile Digital Detector for Detection and Mitigation of Radio Frequency Interference with Microwave Radiometers
The Agile Digital Detector Project is a NASA Instrument Incubator Program project funded by the NASA Earth-Sun Technology Office. ADD is a new type of microwave radiometer detector that is capable of identifying low level Radio Frequency Interference (RFI) and of reducing or eliminating its effect on brightness temperature observations. ADD can discriminate between RFI and natural thermal emission signals by directly measuring other moments of the signal than the variance that is traditionally measured by a conventional square law detector. ADD performance has been experimentally verified in two field deployments, one while connected to a ground based L-Band radiometer operating near an ARSR-1 commercial air traffic control radar and the other while connected to an airborne C-Band radiometer (the NOAA/ETL PSR) installed on a NASA WB-57 flying over major urban centers. The ADD digitizes its pre-detection radiometer signal, performs digital sub band filtering, and then measures the first four moments of the signal's probability density function for each sub band. The second central moment reproduces the square law output of a conventional analog detector. Algorithms that utilize higher order moments are used to detect the presence of RFI.