SAR calibration using frequency-tunable active radar calibrators

In this paper, the impulse response function (IRF) of a synthetic aperture radar (SAR) image of frequency-tunable reference point targets [e.g,, activ e radar calibrator (ARC)] is analyzed, The frequency-tunable ARC is an effe ctive SAR calibration device that can yield a larger radar cross section (R CS or sigma) than a corner reflector, and it displaces the response to a de sirable background area for isolation from brighter man-made targets (e,g,, buildings). SAR calibration accuracy is degraded by Frequency shift, howev er, because of less correlation gain and broader IRF, We compared the theor etically derived IRF with the measurement data and drew the following concl usions: first, the location shift and the peak gain loss can be theoretical ly estimated within 4.2 m and 1.6 dB (one standard deviation); second, the peak calibration method is degraded by the defocused IRF; third, the integr al method, which is not sensitive to defocusing, is recommended for SAR cal ibration; and fourth, the frequency shift should be less than 40 Hz for the satellite-based L-band SAR calibration.