Kalman Tracking and Bayesian Detection for Radar RFI Blanking
Weizhen Dong (Brigham Young U.)
Brian D. Jeffs (Brigham Young U.) bjeffs@ee.byu.edu
J. Richard Fisher (NRAO)

L-Band observations at the Green Bank Telescope (GBT) and other radio observatories are plagued with interference from pulsed aviation RADAR transmissions. Several researchers have studied the problem and proposed time gated blanking and parametric signal subtraction as mitigation strategies [Zhang, Fisher et al Ast. Jour. 126][Ellingson, URSI N. Amer. Mtng. 2003]. One remaining problem is that even when strong direct path pulses and nearby fixed clutter echoes are removed, there are still weaker aircraft echoes present which can corrupt the data. These echoes cannot be excised using fixed time-window blanking synchronized to the RADAR antenna rotation period because they can occur at any time due to the mobile nature of the aircraft. They must be detected before they can be removed, but low echo signal levels which make detection difficult can still corrupt astronomical signal observation. In this paper we present an algorithm which improves aircraft echo blanking by forming a Kalman filter tracker to follow the path of a sequence of echoes observed on successive RADAR antenna sweeps. The tracks developed for each aircraft can be used to predict regions (in bearing and range) for the next expected echoes, even before they are detected. The data in these regions can then be blanked in real time without waiting for the pulse peak to arrive. Additionally, we present a new Bayesian algorithm which combines tracker and pulse detector operations to enable more sensitive weak pulse acquisition. The developed track information is used to form a spatial prior probability distribution for the presence of the next echoes. Regions with higher probability are processed with a lower detection threshold to pull out low level pulses without increasing the overall probability of false alarm detection. Experimental results using real data collected at the BGT are presented.